JP2013021239A - Photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element whose conversion efficiency can be improved.SOLUTION: A photoelectric conversion element 10 includes a transparent conductive film 1, an n-type semiconductor film 2, a p-type semiconductor film 3, an i-type semiconductor film 4, and a photoelectric conversion part 5. The photoelectric conversion part 5 is made of crystalline silicon. The i-type semiconductor film 4 is formed in contact with the photoelectric conversion part 5. The p-type semiconductor film 3 is formed in contact with the i-type semiconductor film 4. The n-type semiconductor film 2 is formed in contact with the p-type semiconductor film 3. The transparent conductive film 1 is formed in contact with the n-type semiconductor film 2. One of the n-type semiconductor film 2 and the p-type semiconductor film 3 comprises an amorphous phase, and the other comprises a microcrystalline phase or an amorphous phase.

Description

  The present invention relates to a photoelectric conversion element.

  Conventionally, the solar cell of patent document 1 is known as a solar cell which converts light into electricity.

  This solar cell includes n-type single crystal silicon, intrinsic amorphous silicon, p-type amorphous silicon, a transparent conductive film, and a back electrode.

  Intrinsic amorphous silicon is formed on one main surface of n-type single crystal silicon. The p-type amorphous silicon is formed on the intrinsic amorphous silicon in contact with the intrinsic amorphous silicon. The transparent conductive film is formed on the p-type amorphous silicon in contact with the p-type amorphous silicon. The back electrode is formed in contact with the n-type single crystal silicon on the side opposite to the transparent conductive film.

JP-A-5-136440

  However, when p-type amorphous silicon is formed in contact with the transparent conductive film as in a conventional solar cell, an energy barrier is formed against holes between the transparent conductive film and the p-type amorphous silicon. Is done. As a result, it becomes difficult to efficiently conduct the photoexcited holes from the p-type amorphous silicon to the transparent conductive film, and the fill factor (FF) of the solar cell is lowered. Moreover, said energy barrier reduces the diffusion potential in a solar cell, and reduces the open circuit voltage of a solar cell.

  Accordingly, the present invention has been made paying attention to a novel problem of solving the deterioration of the characteristics of the solar cell due to the energy barrier, and provides a photoelectric conversion element capable of improving the conversion efficiency.

  According to the embodiment of the present invention, the photoelectric conversion element includes a photoelectric conversion unit, an i-type semiconductor film, a p-type semiconductor film, an n-type semiconductor film, and a transparent conductive film. The photoelectric conversion unit is made of crystalline silicon. The i-type semiconductor film is formed in contact with the photoelectric conversion unit. The p-type semiconductor film is formed in contact with the i-type semiconductor film. The n-type semiconductor film is formed in contact with the p-type semiconductor film. The transparent conductive film is formed in contact with the n-type semiconductor film. One of the p-type semiconductor film and the n-type semiconductor film is made of an amorphous phase, and the other of the p-type semiconductor film and the n-type semiconductor film is made of a microcrystalline phase or an amorphous phase.

  In the photoelectric conversion element according to the embodiment of the present invention, the electrons photoexcited in the photoelectric conversion unit reach the n-type semiconductor film from the photoelectric conversion unit via the external lead wire and the transparent conductive film. Further, the holes photoexcited in the photoelectric conversion unit reach the p-type semiconductor film through the i-type semiconductor film. Since a recombination level exists at the interface between the n-type semiconductor film and the p-type semiconductor film, recombination of electrons and holes at the interface between the n-type semiconductor film and the p-type semiconductor film is promoted. An n / p junction composed of an n-type semiconductor film and a p-type semiconductor film exhibits almost no rectification characteristics due to a recombination level existing at the interface between the n-type semiconductor film and the p-type semiconductor film, A decrease in internal potential at the junction composed of the p-type semiconductor film / i-type semiconductor film / photoelectric conversion portion is suppressed. As a result, the open circuit voltage and the fill factor of the photoelectric conversion element are improved.

  Therefore, the conversion efficiency of the photoelectric conversion element can be improved.

It is sectional drawing which shows the structure of the photoelectric conversion element by embodiment of this invention. 3 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 1. FIG. It is an energy band figure of the photoelectric conversion element shown in FIG. 6 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 2. FIG. 6 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 3. FIG. 6 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 4. FIG. 10 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 5. FIG. It is an energy band figure of the photoelectric conversion element shown in FIG.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  In this specification, the “amorphous phase” refers to a state in which silicon (Si) atoms and the like are randomly arranged. The “microcrystalline phase” refers to a state in which crystal grains such as Si having a grain diameter of about 10 to 100 nm exist in a random network such as Si atoms. Furthermore, although amorphous silicon is described as “a-Si”, this notation actually means that hydrogen (H) atoms are included. Amorphous silicon carbide (a-SiC), amorphous silicon germanium (a-SiGe), amorphous germanium (a-Ge), microcrystalline silicon carbide (μc-SiC), microcrystalline silicon (μc-Si), microcrystalline silicon germanium ( Similarly, μc-SiGe) and microcrystalline germanium (μc-Ge) mean that H atoms are contained.

  FIG. 1 is a cross-sectional view showing a configuration of a photoelectric conversion element according to an embodiment of the present invention. Referring to FIG. 1, a photoelectric conversion element 10 according to an embodiment of the present invention includes a transparent conductive film 1, an n-type semiconductor film 2, a p-type semiconductor film 3, an i-type semiconductor film 4, and a photoelectric conversion unit. 5.

The transparent conductive film 1 is made of, for example, ITO (Indium Tin Oxide), SnO _2, ZnO, or the like.

  The n-type semiconductor film 2 is disposed in contact with the transparent conductive film 1. The n-type semiconductor film 2 is made of an amorphous phase or a microcrystalline phase when the p-type semiconductor film 3 is made of an amorphous phase. The n-type semiconductor film 2 is made of an amorphous phase when the p-type semiconductor film 3 is made of a microcrystalline phase.

  The p-type semiconductor film 3 is disposed in contact with the n-type semiconductor film 2. The p-type semiconductor film 3 is made of an amorphous phase or a microcrystalline phase when the n-type semiconductor film 2 is made of an amorphous phase. The p-type semiconductor film 3 is made of an amorphous phase when the n-type semiconductor film 2 is made of a microcrystalline phase.

  The i-type semiconductor film 4 is disposed in contact with the p-type semiconductor film 3. The i-type semiconductor film 4 is made of an amorphous phase.

  The photoelectric conversion unit 5 is disposed in contact with the i-type semiconductor film 4. The photoelectric conversion unit 5 is made of single crystal silicon or polycrystalline silicon. That is, the photoelectric conversion unit 5 is made of crystalline silicon.

  In the photoelectric conversion element 10, sunlight is incident on the photoelectric conversion element 10 from the transparent conductive film 1 side.

  The photoelectric conversion element 10 is manufactured by sequentially laminating the i-type semiconductor film 4, the p-type semiconductor film 3, the n-type semiconductor film 2, and the transparent conductive film 1 on the photoelectric conversion unit 5.

  As described above, one of the n-type semiconductor film 2 and the p-type semiconductor film 3 is made of an amorphous phase, and the other of the n-type semiconductor film 2 and the p-type semiconductor film 3 is an amorphous phase or a microcrystalline phase. Therefore, a recombination level exists at the interface between the n-type semiconductor film 2 and the p-type semiconductor film 3. In addition, the junction composed of the n-type semiconductor film 2 and the p-type semiconductor film 3 exhibits almost no rectification characteristics due to the recombination level existing at the interface of the n-type semiconductor film 2 / p-type semiconductor film 3. A decrease in the diffusion potential in the p-type semiconductor film 3 / i-type semiconductor film 4 / photoelectric conversion unit 5 is suppressed.

As a result, the holes photoexcited by the photoelectric conversion unit 5 move to the p-type semiconductor film 3 by carrier diffusion and the diffusion potential, and reach the interface between the n-type semiconductor film 2 and the p-type semiconductor film 3. The electrons photoexcited by the photoelectric conversion unit 5 reach the n-type semiconductor film 2 from the photoelectric conversion unit 5 through an external lead wire (not shown) and the transparent conductive film 1. Then, electrons and holes are recombined through a recombination level at the interface between the n-type semiconductor film 2 and the p-type semiconductor film 3. As a result, the photocurrent _Iph flows through the photoelectric conversion element 10.

  As described above, by providing the n-type semiconductor film 2 between the transparent conductive film 1 and the p-type semiconductor film 3, the holes photoexcited by the photoelectric conversion unit 5 are converted into the n-type semiconductor film 2 and the p-type semiconductor film. 3 recombines with electrons efficiently at the interface with 3.

  Therefore, the decrease in the diffusion potential and the decrease in the fill factor due to the energy barrier formed when the p-type semiconductor film is formed in contact with the transparent conductive film can be suppressed, and the conversion efficiency of the photoelectric conversion element 10 can be improved.

  When the n-type semiconductor film 2 is made of an amorphous phase and the p-type semiconductor film 3 is made of a microcrystalline phase, the diffusion potential in the p-type semiconductor film 3 / i-type semiconductor film 4 / photoelectric conversion unit 5 is p-type. Since the semiconductor film 3 becomes larger than that of the amorphous phase, the open circuit voltage Voc can be increased. In addition, when the p-type semiconductor film 3 is made of a microcrystalline phase, the resistance of the p-type semiconductor film 3 is lower than when the p-type semiconductor film 3 is made of an amorphous phase, so that the fill factor FF can be improved. As a result, the conversion efficiency of the photoelectric conversion element 10 can be further improved.

  Hereinafter, examples of the photoelectric conversion element 10 will be described. When the photoelectric conversion element 10 is specifically realized, the n-type semiconductor film 2, the p-type semiconductor film 3, and the i-type semiconductor film 4 are made of one of the n-type semiconductor film 2 and the p-type semiconductor film 3 from an amorphous phase. And each of the materials shown in Table 1 under the condition that the other of the n-type semiconductor film 2 and the p-type semiconductor film 3 is made of an amorphous phase or a microcrystalline phase.

Example 1
FIG. 2 is a cross-sectional view illustrating a configuration of the photoelectric conversion element according to the first embodiment. Referring to FIG. 2, photoelectric conversion element 10 </ b> A includes current collecting electrode 9, transparent conductive film 11, n-type amorphous film 21, p-type amorphous film 31, and i-type amorphous film 41. A photoelectric conversion unit 51, an insulating layer 61, and a back electrode 62.

  The i-type amorphous film 41, the p-type amorphous film 31, the n-type amorphous film 21, the transparent conductive film 11, and the current collecting electrode 9 are sequentially stacked on the photoelectric conversion unit 51. The insulating layer 61 and the back electrode 62 are sequentially stacked on the photoelectric conversion unit 51 on the side opposite to the transparent conductive film 11.

  The current collecting electrode 9 is made of, for example, silver (Ag), and is formed in a comb shape on the surface of the transparent conductive film 11.

The transparent conductive film 11 is made of, for example, SnO _2. The n-type amorphous film 21 is made of, for example, n-type a-Si, and has a film thickness of, for example, 5 nm. The phosphorus (P) concentration in the n-type amorphous film 21 is 5 × 10 ²⁰ cm ^{−3 to} 7 × 10 ²⁰ cm ⁻³ . The n-type amorphous film 21 is in contact with the transparent conductive film 11.

  The p-type amorphous film 31 is made of, for example, p-type a-Si, and has a film thickness of, for example, 10 nm. The p-type amorphous film 31 is in contact with the n-type amorphous film 21.

  The i-type amorphous film 41 is made of, for example, i-type a-Si and has a film thickness of, for example, 10 nm. The i-type amorphous film 41 is in contact with the p-type amorphous film 31.

  The photoelectric conversion unit 51 is made of, for example, n-type single crystal silicon having a plane orientation of (100) and a specific resistance of 0.1 to 1.0 Ω · cm, and has a thickness of, for example, 200 to 300 μm. The photoelectric conversion unit 51 is in contact with the i-type amorphous film 41.

The insulating layer 61 has, for example, a two-layer structure of silicon dioxide (SiO ₂ ) and silicon nitride (SiN). The insulating layer 61 is formed on the surface of the photoelectric conversion unit 51 so that SiO ₂ is in contact with the photoelectric conversion unit 51.

  The back electrode 62 is made of, for example, aluminum (Al). The back electrode 62 is in contact with the photoelectric conversion unit 51 through the through hole formed in the insulating layer 61 and covers the insulating layer 61.

  As described above, the photoelectric conversion element 10A embodies the photoelectric conversion element 10 by using the amorphous film for all of the n-type semiconductor film 2, the p-type semiconductor film 3, and the i-type semiconductor film 4 of the photoelectric conversion element 10. Is.

  A method for manufacturing the photoelectric conversion element 10A will be described. The photoelectric conversion element 10A is manufactured by a plasma CVD (Chemical Vapor Deposition) method using a plasma apparatus.

  The plasma apparatus includes a preparation chamber, reaction chambers CB1 to CB3, an extraction chamber, a matching unit, and an RF power source. The charging chamber, the reaction chambers CB1 to CB3, and the take-out chamber are linearly arranged. A partition valve is used to partition between the charging chamber and the reaction chamber CB1, between the reaction chamber CB1 and the reaction chamber CB2, between the reaction chamber CB2 and the reaction chamber CB3, and between the reaction chamber CB3 and the take-out chamber. It has been. In addition, the plasma apparatus is provided with a transfer mechanism for sequentially transferring silicon wafers from the preparation chamber to the reaction chamber CB1, the reaction chamber CB2, the reaction chamber CB3, and the take-out chamber.

The charging chamber includes a heating mechanism and an exhaust mechanism. The heating mechanism raises the temperature of the silicon wafer to a predetermined temperature. The exhaust mechanism exhausts the gas in the preparation chamber, and sets the ultimate pressure in the preparation chamber to, for example, 1 × 10 ⁻⁵ Pa or less.

Each of the reaction chambers CB1 to CB3 includes a parallel plate electrode, a heating mechanism, and an exhaust mechanism. The heating mechanism raises the temperature of the silicon wafer to a predetermined temperature. The exhaust mechanism exhausts the gases in the reaction chambers CB1 to CB3, and sets the ultimate pressure in the reaction chambers CB1 to CB3 to, for example, 1 × 10 ⁻⁵ Pa or less. The parallel plate electrodes are connected to an RF power source through a matching unit.

The take-out chamber includes an exhaust mechanism. The exhaust mechanism exhausts the gas in the extraction chamber and sets the ultimate pressure in the extraction chamber to, for example, 1 × 10 ⁻⁵ Pa or less.

  Each exhaust mechanism of the preparation chamber, the reaction chambers CB1 to CB3, and the take-out chamber includes a turbo molecular pump, a mechanical booster pump, and a rotary pump. The turbo molecular pump, mechanical booster pump and rotary pump are connected in series to the charging chamber, reaction chambers CB1 to CB3, and the extraction chamber so that the turbo molecular pump is closest to the charging chamber, reaction chambers CB1 to CB3 and the extraction chamber. Has been. Each exhaust mechanism exhausts the gas in the charging chamber, reaction chambers CB1 to CB3 and the extraction chamber by a turbo molecular pump, a mechanical booster pump and a rotary pump, or the charging chamber and reaction chamber CB1 by a mechanical booster pump and a rotary pump. The gas in CB3 and the extraction chamber is exhausted.

  The RF power source applies, for example, RF power of 13.56 MHz to the parallel plate electrodes of the reaction chambers CB1 to CB3 via the matching unit.

  When manufacture of the photoelectric conversion element 10A is started, a silicon wafer made of n-type single crystal silicon as the photoelectric conversion unit 51 is ultrasonically cleaned with ethanol or the like to degrease, and then the silicon wafer is immersed in hydrofluoric acid. The natural oxide film formed on the surface of the n-type single crystal silicon is removed, and the surface of the n-type single crystal silicon is terminated with hydrogen.

  When texturing the surface of n-type single crystal silicon, the silicon wafer is ultrasonically cleaned with ethanol or the like, and then the silicon wafer surface is chemically anisotropically etched using an alkali to obtain n-type single crystal silicon. Texture the surface. Thereafter, the natural oxide film is removed using hydrofluoric acid as described above, and the surface of the n-type single crystal silicon is terminated with hydrogen.

  When the cleaning of the silicon wafer is completed, the silicon wafer is placed on the substrate holder in the preparation chamber of the plasma apparatus.

The charging chamber exhaust mechanism exhausts the gas in the charging chamber to 1 × 10 ⁻⁵ Pa or less, and the charging chamber heating mechanism sets the temperature of the silicon wafer (n-type single crystal silicon) to 200 ° C. Heat the substrate holder. Further, the heating mechanism of the reaction chambers CB1 to CB3 also heats the substrate holder so that the temperature of the silicon wafer (n-type single crystal silicon) is set to 200 ° C.

  When the temperature of the silicon wafer (n-type single crystal silicon) reaches 200 ° C., the partition valve between the charging chamber and the reaction chamber CB1 is opened, and the silicon wafer (n-type single crystal silicon) is moved from the charging chamber to the reaction chamber. Transported to CB1.

  Table 2 shows the flow rate of the material gas when forming the n-type amorphous film 21, the p-type amorphous film 31, and the i-type amorphous film 41.

When the silicon wafer (n-type single crystal silicon) is transferred to the reaction chamber CB1, 10 sccm of silane (SiH ₄ ) gas and 100 sccm of hydrogen (H ₂ ) gas are allowed to flow into the reaction chamber CB1, and the pressure in the reaction chamber CB1 is increased. Is set in the range of 13.3 Pa to 665 Pa. The RF power source applies RF power in the range of 16 to 80 mW / cm ² to the parallel plate electrodes through the matching unit. Thereby, plasma is generated in the reaction chamber CB1, and i-type a-Si as the i-type amorphous film 41 is deposited on one main surface of the n-type single crystal silicon.

When the film thickness of the i-type amorphous film 41 reaches 10 nm, the application of RF power to the parallel plate electrodes in the reaction chamber CB1 is stopped and the supply of SiH ₄ gas and H ₂ gas to the reaction chamber CB1 is stopped. Then, the reaction chamber CB1 is evacuated to 1 × 10 ⁻⁵ Pa or less by an exhaust mechanism. Then, the partition valve is opened, and the i-type amorphous film 41 / n-type single crystal silicon is transferred from the reaction chamber CB1 to the reaction chamber CB2.

When the i-type amorphous film 41 / n-type single crystal silicon is transferred to the reaction chamber CB2, 2 sccm of SiH ₄ gas, 42 sccm of H ₂ gas, and 12 sccm of diborane (B ₂ H ₆ ) diluted with hydrogen are used. Gas is allowed to flow into the reaction chamber CB2, and the pressure in the reaction chamber CB2 is set in the range of 13.3 Pa to 665 Pa. The RF power source applies RF power in the range of 16 to 80 mW / cm ² to the parallel plate electrodes through the matching unit. The concentration of B ₂ H ₆ gas diluted with hydrogen is 0.1%.

  As a result, plasma is generated in the reaction chamber CB2, and p-type a-Si as the p-type amorphous film 31 is deposited on the i-type amorphous film 41.

When the thickness of the p-type amorphous film 31 reaches 10 nm, the application of RF power to the parallel plate electrodes in the reaction chamber CB2 is stopped, and the reaction chamber CB2 for SiH ₄ gas, H ₂ gas and B ₂ H ₆ gas is used. The reaction chamber CB2 is evacuated to 1 × 10 ⁻⁵ Pa or less by an exhaust mechanism. Then, the gate valve is opened, and the p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon is transferred from the reaction chamber CB2 to the reaction chamber CB3.

When the p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon is transferred to the reaction chamber CB3, 20 sccm of SiH ₄ gas, 150 sccm of H ₂ gas, and hydrogen diluted 50 sccm. The phosphine (PH ₃ ) gas is allowed to flow into the reaction chamber CB3, and the pressure in the reaction chamber CB3 is set to a range of 13.3 Pa to 665 Pa. The RF power source applies RF power in the range of 16 to 80 mW / cm ² to the parallel plate electrodes through the matching unit.

As a result, plasma is generated in the reaction chamber CB 3, and n-type a-Si as the n-type amorphous film 21 is deposited on the p-type amorphous film 31. The concentration of PH ₃ gas diluted with hydrogen is 0.2%.

When the thickness of the n-type amorphous film 21 reaches 5 nm, the application of RF power to the parallel plate electrodes in the reaction chamber CB3 is stopped, and SiH ₄ gas, H ₂ gas, and PH ₃ gas are supplied to the reaction chamber CB3. The supply is stopped, and the reaction chamber CB3 is evacuated to 1 × 10 ⁻⁵ Pa or less by an exhaust mechanism. Then, the partition valve is opened, and the n-type amorphous film 21 / p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon is transferred from the reaction chamber CB3 to the take-out chamber.

  Then, after cooling the n-type amorphous film 21 / p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon to room temperature in the extraction chamber, the n-type amorphous film 21 / p Type amorphous film 31 / i type amorphous film 41 / n type single crystal silicon is taken out from the extraction chamber, and n type amorphous film 21 / p type amorphous film 31 / i type amorphous film 41 / n-type single crystal silicon is set in a sputtering apparatus.

Then, SnO ₂ as the transparent conductive film 11 is formed on the n-type amorphous film 21 by sputtering, and then Ag as the collecting electrode 9 is formed on the transparent conductive film 11 by sputtering using a metal mask. Form.

Subsequently, SiO ₂ and SiN are sequentially laminated on the surface of the n-type single crystal silicon opposite to the transparent conductive film 11 by a sputtering method.

Then, collecting electrode 9 / transparent conductive film 11 / n-type amorphous film 21 / p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon / SiO ₂ / SiN from the sputtering apparatus. Take out. Then, the collector electrode 9 / transparent conductive film 11 / n-type amorphous film 21 / p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon / SiO ₂ / SiN SiN surface A resist is applied to the substrate, and the applied resist is patterned into a predetermined pattern by photolithography.

Thereafter, SiO ₂ / SiN is etched using the resist pattern as a mask. The etching of SiO ₂ / SiN may be chemical wet etching or dry etching using plasma.

Then, the resist pattern is removed, and a back electrode (Al) is formed on the entire surface of the etched SiO ₂ / SiN by vapor deposition or the like. Thereby, the photoelectric conversion element 10A is completed.

As described above, the photoelectric conversion element 10A includes the i-type amorphous film 41, the p-type amorphous film 31, and the n-type amorphous film 21 sequentially stacked on one main surface of the photoelectric conversion unit 51 by the plasma CVD method. Thereafter, the transparent conductive film 11 (SnO ₂ ) and the collector electrode 9 (Ag) are sequentially stacked on the n-type amorphous film 21 by sputtering, and the insulating layer 61 (SiO ₂ / SiN) and the back electrode 62 are then stacked. It is manufactured by sequentially stacking (Al) on the other surface of the photoelectric conversion unit 51.

  FIG. 3 is an energy band diagram of the photoelectric conversion element 10A shown in FIG. In FIG. 3, the collecting electrode 9, the insulating layer 61, and the back electrode 62 are omitted.

  Referring to FIG. 3, n-type amorphous film 21 and p-type amorphous film 31 have an optical band gap of 1.8 eV and an activation energy of 0.20 eV. Has an optical band gap of 1.74 eV and an activation energy of 0.73 eV, and the n-type single crystal silicon as the photoelectric conversion unit 51 has an optical band gap of 1.1 eV and 0.4 to 0.5 eV. Has activation energy.

  As a result, the p-type amorphous film 31 and the i-type amorphous film 41 form a heterojunction, and the i-type amorphous film 41 and the n-type single crystal silicon (photoelectric conversion unit 51) also form a heterojunction. Form.

  The n-type amorphous film 21 is made of n-type a-Si, and the p-type amorphous film 31 is made of p-type a-Si. The n-type amorphous film 21 (n-type a-Si) is in contact with the p-type amorphous film 31 (p-type a-Si) by the plasma CVD method, and the p-type amorphous film 31 (p-type a-Si). Deposited on -Si). As a result, when the n-type amorphous film 21 (n-type a-Si) is deposited, the P atoms in the n-type amorphous film 21 (n-type a-Si) and the p-type amorphous film 31 (p-type). Boron (B) atoms in a-Si) diffuse to each other. Therefore, a recombination level exists at the interface between the n-type amorphous film 21 and the p-type amorphous film 31. And since this recombination level exists, the junction (n / p junction) which consists of the n-type amorphous film 21 and the p-type amorphous film 31 hardly shows a rectification characteristic. As a result, the diffusion potential (= internal potential Vbi) of the pin junction made of the p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon (photoelectric conversion unit 51) hardly decreases.

  Further, by inserting the i-type amorphous film 41 between the p-type amorphous film 31 and the n-type single crystal silicon (photoelectric conversion portion 51), the B atoms in the p-type amorphous film 31 and , P atoms in n-type single crystal silicon (photoelectric conversion part 51) are prevented from intermingling with each other, and dangling bonds existing on the surface of n-type single crystal silicon (photoelectric conversion part 51) are replaced with H atoms. Terminate with. As a result, carriers (electrons and holes) are regenerated at the interface of the p-type amorphous film 31 / i-type amorphous film 41 and the interface of the i-type amorphous film 41 / n-type single crystal silicon (photoelectric conversion unit 51). Bonding is reduced.

Furthermore, since SiO _{2 of the} insulating layer 61 is in contact with the n-type single crystal silicon (photoelectric conversion portion 51), electrons and holes at the interface of the n-type single crystal silicon (photoelectric conversion portion 51) / insulating layer 61 (SiO ₂ ). Recombination is reduced.

  Then, the photoexcited holes in the n-type single crystal silicon (photoelectric conversion unit 51) move to the i-type amorphous film 41 side by carrier diffusion, and move to the p-type amorphous film 31 by the internal potential Vbi. . The electrons photoexcited in the n-type single crystal silicon (photoelectric conversion unit 51) move to the back electrode 62 side by carrier diffusion.

Then, the electrons reach the n-type amorphous film 21 through the back electrode 62, an external lead wire (not shown), and the transparent conductive film 11. In this case, the interface between the n-type amorphous film 21 and the p-type amorphous film 31, since the energy barrier phi _n for electrons exists, electrons in the n-type amorphous film in 21, p-type non It cannot move to the crystalline film 31.

Further, the interface between the p-type amorphous film 31 and the n-type amorphous film 21, the energy barrier phi _p for holes is present, holes in the p-type amorphous film in 31 a transparent conductive It cannot move to the film 11.

As a result, electrons and holes recombine efficiently through recombination levels at the interface between the n-type amorphous film 21 and the p-type amorphous film 31. As described above, since the P concentration in the n-type amorphous film 21 is 5 × 10 ²⁰ cm ^{−3 to} 7 × 10 ²⁰ cm ⁻³ , the n-type amorphous film 21 and the p-type amorphous film The recombination level at the interface with the film 31 increases, and electrons and holes recombine efficiently through this recombination level. Thus, the photoelectric conversion element 10A, the flow photocurrent I _ph, the fill factor FF is improved than the case where the p-type amorphous film 31 is in contact with the transparent conductive film 11.

Further, as described above, the n / p junction composed of the n-type amorphous film 21 and the p-type amorphous film 31 hardly reduces the internal potential Vbi and separates electrons and holes by the internal potential Vbi. the effect is large, the voltage at which the photocurrent I _ph is zero (open circuit voltage Voc) is greater than the case where the p-type amorphous film 31 is in contact with the transparent conductive film 11.

  Therefore, the conversion efficiency of the photoelectric conversion element 10 </ b> A can be improved by providing the n-type amorphous film 21 between the transparent conductive film 11 and the p-type amorphous film 31.

  In the photoelectric conversion element 10A, the total thickness of the n-type amorphous film 21, the p-type amorphous film 31, and the i-type amorphous film 41 is 25 nm. is there. Accordingly, by applying an amorphous film to all of the n-type semiconductor film 2, the p-type semiconductor film 3, and the i-type semiconductor film 4, a conventional crystalline silicon-based photoelectric conversion in which a p / n junction is formed by thermal diffusion. Compared to the element, the junction depth becomes shallower and the distribution of the dopant (B) in the thickness direction of the photoelectric conversion element 10A becomes steep.

  As a result, electrons and holes can be generated by incident light in the entire region in the thickness direction of the photoelectric conversion unit 51 (n-type single crystal silicon), and the n-type amorphous film 21 / p-type amorphous film 31 is generated. The short-circuit current density can be increased by a synergistic effect of promoting recombination of electrons and holes at the interface.

The n-type amorphous film 21 may be made of any of n-type a-SiC, n-type a-SiGe, and n-type a-Ge in addition to n-type a-Si. In this case, n-type a-SiC is formed by the above-described plasma CVD method using SiH ₄ gas, methane (CH ₄ ) gas, PH ₃ gas, and H ₂ gas as material gases. The n-type a-SiGe is formed by the above-described plasma CVD method using SiH ₄ gas, germane (GeH ₄ ) gas, PH ₃ gas, and H ₂ gas as material gases. The n-type a-Ge is formed by the above-described plasma CVD method using GeH ₄ gas, PH ₃ gas, and H ₂ gas as material gases.

The p-type amorphous film 31 may be made of any of p-type a-SiC, p-type a-SiGe, and p-type a-Ge in addition to p-type a-Si. In this case, p-type a-SiC is formed by the above-described plasma CVD method using SiH ₄ gas, CH ₄ gas, B ₂ H ₆ gas, and H ₂ gas as material gases. The p-type a-SiGe is formed by the above-described plasma CVD method using SiH ₄ gas, GeH ₄ gas, B ₂ H ₆ gas and H ₂ gas as material gases. The p-type a-Ge is formed by the above-described plasma CVD method using GeH ₄ gas, B ₂ H ₆ gas, and H ₂ gas as material gases.

Further, the i-type amorphous film 41 may be made of either i-type a-SiC or i-type a-SiGe in addition to i-type a-Si. In this case, i-type a-SiC is formed by the above-described plasma CVD method using SiH ₄ gas, CH ₄ gas, and H ₂ gas as material gases. i-type a-SiGe is formed by the above-described plasma CVD method using SiH ₄ gas, GeH ₄ gas, and H ₂ gas as material gases.

  Note that i-type a-Ge is also assumed as the i-type amorphous film 41, but i-type a-Ge has an optical band gap smaller than that of n-type single crystal silicon. When used as the i-type amorphous film 41, it is difficult to improve the open circuit voltage Voc. This is because in the photoelectric conversion element 10A, the optical band gap of the i-type amorphous film 41 dominantly determines the open circuit voltage Voc.

  Therefore, in the embodiment of the present invention, i-type a-SiC, i-type a-Si, and i-type a-SiGe, which are larger than the optical band gap of n-type single crystal silicon (photoelectric conversion unit 51), are converted into i-type non-crystal. The crystalline film 41 was used.

  Further, by applying a-Si or the like to the n-type amorphous film 21, the p-type amorphous film 31, and the i-type amorphous film 41, the n-type amorphous film 21, the p-type amorphous film 31 and the i-type amorphous film 41 are continuously stacked on the photoelectric conversion unit 51 (n-type single crystal silicon) at a low temperature of about 200 ° C. by plasma CVD. The insulating layer 61 and the back electrode 62 are also laminated on the photoelectric conversion unit 51 (n-type single crystal silicon) by a sputtering method at a temperature of 200 ° C. or lower. As a result, it is possible to prevent the quality of the n-type single crystal silicon as the photoelectric conversion unit 51 from being deteriorated due to thermal damage.

  As described above, in Example 1, the n-type amorphous film 21, the p-type amorphous film 31, and the i-type amorphous film 41 are a-SiC, a-Si, and a-SiGe shown in Table 1. , A-Ge or other amorphous material.

  Then, as in the case where the p-type amorphous film 31 is made of p-type a-SiGe and the i-type amorphous film 41 is made of i-type a-Si, the optical band gap of the p-type amorphous film 31 is used. Is smaller than the optical band gap of the i-type amorphous film 41, the end of the valence band of p-type a-SiGe is the end of the valence band of i-type a-Si in the energy band diagram of the photoelectric conversion element 10A. Lower in energy. That is, the end of the valence band of p-type a-SiGe is positioned above the end of the valence band of i-type a-Si in the paper of FIG. As a result, the holes photoexcited in the photoelectric conversion unit 51 (n-type single crystal silicon) reach the p-type amorphous film 31 and then are confined in the p-type amorphous film 31 to be n-type amorphous. At the interface of the film 21 / p-type amorphous film 31, recombination of electrons and holes is promoted.

  Therefore, by producing the photoelectric conversion element 10A using an amorphous material in which the optical band gap of the p-type amorphous film 31 is smaller than the optical band gap of the i-type amorphous film 41, the photoelectric conversion element 10A. The conversion efficiency can be improved.

  In addition, the photoelectric conversion part 51 of the photoelectric conversion element 10A in Example 1 may be made of n-type polycrystalline silicon. In this case, the n-type polycrystalline silicon has, for example, a specific resistance of 0.1 to several Ω · cm and a thickness of 200 to 300 μm.

  When n-type polycrystalline silicon is applied to the photoelectric conversion unit 51, preferably, the n-type polycrystalline silicon is subjected to hydrogen plasma treatment at a temperature of 200 ° C. or lower, and then the i-type amorphous film 41, p-type non-crystalline silicon is processed. The crystalline film 31 and the n-type amorphous film 21 are sequentially stacked on the n-type polycrystalline silicon by the plasma CVD method to manufacture the photoelectric conversion element 10A. Thereby, the grain boundary of n-type polycrystalline silicon is passivated by H atoms, and recombination of carriers (electrons and holes) at the grain boundary can be reduced.

  Further, the surface of the n-type polycrystalline silicon may have an uneven structure (texture structure). In this case, the surface of the n-type polycrystalline silicon is roughened by plasma etching, reactive ion etching, or the like.

(Example 2)
FIG. 4 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 2. With reference to FIG. 4, the photoelectric conversion element 10 </ b> B in Example 2 is the same as the photoelectric conversion element 10 </ b> A except that the photoelectric conversion unit 51 of the photoelectric conversion element 10 </ b> A is replaced with a photoelectric conversion unit 71.

  As described above, the photoelectric conversion element 10B uses an amorphous film for all of the n-type semiconductor film 2, the p-type semiconductor film 3, and the i-type semiconductor film 4 of the photoelectric conversion element 10 similarly to the photoelectric conversion element 10A. The photoelectric conversion element 10 is embodied.

  The photoelectric conversion unit 71 is made of, for example, p-type single crystal silicon having a plane orientation of (100) and a specific resistance of 0.1 to 1.0 Ω · cm, and has a thickness of, for example, 200 to 300 μm. The photoelectric conversion unit 71 has one surface in contact with the i-type amorphous film 41 and the other surface in contact with the insulating layer 61 and the back electrode 62.

  As described above, the photoelectric conversion element 10B includes the i-type amorphous film 41, the p-type amorphous film 31, the n-type amorphous film 21, the transparent conductive film 11, and the collecting electrode 9 that are connected to the photoelectric conversion unit 71 (p The insulating layer 61 and the back surface electrode 62 are sequentially stacked on the other surface of the photoelectric conversion portion 71 (p-type single crystal silicon).

  A method for manufacturing the photoelectric conversion element 10B will be described. A silicon wafer made of p-type single crystal silicon as the photoelectric conversion unit 71 is cleaned by the method described above. In this case, the surface of the p-type single crystal silicon may be textured similarly to the n-type single crystal silicon as the photoelectric conversion unit 51.

  Then, a silicon wafer (p-type single crystal silicon) is set in the plasma apparatus, and the i-type amorphous film 41, the p-type amorphous film 31 and the n-type amorphous film are formed by the plasma CVD method using the conditions described above. The film 21 is sequentially stacked on the p-type single crystal silicon (photoelectric conversion unit 71).

  Thereafter, the transparent conductive film 11 and the collector electrode 9 are sequentially stacked on the n-type amorphous film 21 by the method described above. Then, the insulating layer 61 and the back electrode 62 are sequentially stacked on the other surface of the p-type single crystal silicon (photoelectric conversion portion 71) by the method described above.

  Thereby, the photoelectric conversion element 10B is completed.

  The energy band diagram of the photoelectric conversion element 10B is substantially the same as the energy band diagram of the photoelectric conversion element 10A shown in FIG. 3, and the power generation mechanism in the photoelectric conversion element 10B is the same as that of the photoelectric conversion element 10A.

  Accordingly, electrons and holes are efficiently recombined through recombination levels at the interface between the n-type amorphous film 21 and the p-type amorphous film 31.

  Also in the photoelectric conversion element 10B, the n / p junction composed of the n-type amorphous film 21 and the p-type amorphous film 31 has a p-type amorphous film 31 / i-type amorphous film for the reason described above. The internal potential Vbi of the junction made of the mass film 41 / p-type single crystal silicon (photoelectric conversion portion 71) is hardly lowered.

  As a result, even when p-type single crystal silicon is used as the photoelectric conversion unit 71, the open circuit voltage Voc and the fill factor FF are improved, and the conversion efficiency of the photoelectric conversion element 10B can be improved.

  In addition, the photoelectric conversion part 71 of the photoelectric conversion element 10B in Example 2 may be made of p-type polycrystalline silicon. In this case, the p-type polycrystalline silicon has, for example, a specific resistance of 0.1 to several Ω · cm and a thickness of 200 to 300 μm.

  When p-type polycrystalline silicon is applied to the photoelectric conversion unit 71, preferably, the p-type polycrystalline silicon is subjected to hydrogen plasma treatment at a temperature of 200 ° C. or lower, and then the i-type amorphous film 41, p-type non-crystalline film is formed. The crystalline film 31 and the n-type amorphous film 21 are sequentially stacked on the p-type polycrystalline silicon by the plasma CVD method to manufacture the photoelectric conversion element 10B. Thereby, the grain boundary of p-type polycrystalline silicon is passivated by H atoms, and recombination of carriers (electrons and holes) at the grain boundary can be reduced.

  Further, the surface of the p-type polycrystalline silicon may have an uneven structure (texture structure). In this case, the surface of the p-type polycrystalline silicon is roughened by plasma etching, reactive ion etching, or the like.

  The other description about the photoelectric conversion element 10B is the same as the description about the photoelectric conversion element 10A.

(Example 3)
FIG. 5 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 3. Referring to FIG. 5, photoelectric conversion element 10 </ b> C is obtained by replacing p-type amorphous film 31 of photoelectric conversion element 10 </ b> A shown in FIG. 2 with p-type microcrystalline film 81, and the other is photoelectric conversion element 10 </ b> A. Is the same.

  Thus, the photoelectric conversion element 10 </ b> C uses an amorphous film for the n-type semiconductor film 2 and the i-type semiconductor film 4 of the photoelectric conversion element 10, and uses a microcrystalline film for the p-type semiconductor film 3 of the photoelectric conversion element 10. Thus, the photoelectric conversion element 10 is embodied.

  The p-type microcrystalline film 81 is made of, for example, p-type μc-Si and has a film thickness of, for example, 10 nm. The p-type microcrystalline film 81 is disposed between the n-type amorphous film 21 and the i-type amorphous film 41 in contact with the n-type amorphous film 21 and the i-type amorphous film 41. .

  As described above, the photoelectric conversion element 10C includes the i-type amorphous film 41, the p-type microcrystalline film 81, the n-type amorphous film 21, the transparent conductive film 11, and the collecting electrode 9 that are connected to the photoelectric conversion unit 51 (n-type). Single-crystal silicon) is sequentially laminated on one surface, and the insulating layer 61 and the back electrode 62 are sequentially laminated on the other surface of the photoelectric conversion portion 51 (n-type single-crystal silicon).

  A method for manufacturing the photoelectric conversion element 10C will be described. Table 3 shows the flow rates of the material gases when forming the n-type amorphous film 21, the p-type microcrystalline film 81, and the i-type amorphous film 41.

  A silicon wafer made of n-type single crystal silicon as the photoelectric conversion unit 51 is cleaned by the method described above. Then, a silicon wafer (n-type single crystal silicon) is set in the plasma apparatus, and the i-type amorphous film 41 is formed on the n-type single crystal silicon (photoelectric conversion unit 51) using the above-described conditions by plasma CVD. accumulate.

Thereafter, the p-type microcrystalline film 81 is converted into the i-type amorphous film 41 by plasma CVD using ₂ sccm of SiH ₄ gas, 140 sccm of H ₂ gas, and 12 sccm of B ₂ H ₆ gas diluted with hydrogen as material gases. / N-type single crystal silicon (photoelectric conversion unit 51). In this case, the pressure in the reaction chamber CB2 is in the range of 13.3 Pa to 665 Pa, and the RF power is in the range of 16 to 80 mW / cm ² .

When the thickness of the p-type microcrystalline film 81 reaches 10 nm, the application of RF power to the parallel plate electrode and the supply of SiH ₄ gas, H ₂ gas, and B ₂ H ₆ gas to the reaction chamber CB ₂ are stopped.

  Subsequently, the n-type amorphous film 21 is deposited on the p-type microcrystalline film 81 / i-type amorphous film 41 / n-type single crystal silicon (photoelectric conversion portion 51) using the above-described conditions by plasma CVD. To do.

  Thereafter, the transparent conductive film 11 and the collector electrode 9 are sequentially stacked on the n-type amorphous film 21 by the method described above. Then, the insulating layer 61 and the back electrode 62 are sequentially stacked on the other surface of the n-type single crystal silicon (photoelectric conversion unit 51) by the method described above.

  Thereby, the photoelectric conversion element 10C is completed.

  In the photoelectric conversion element 10C, the n-type amorphous film 21 (n-type a-Si) is in contact with the p-type microcrystalline film 81 (p-type μc-Si) by a plasma CVD method. deposited on p-type [mu] c-Si). As a result, the P atoms in the n-type amorphous film 21 (n-type a-Si) and the B atoms in the p-type microcrystalline film 81 (p-type μc-Si) diffuse to each other. Therefore, the n-type amorphous film 21 / p-type microcrystalline film 81 has a recombination level.

  The p-type microcrystalline film 81 has an optical band gap of 1.97 eV larger than the above-described p-type amorphous film 31 and an activation smaller than the p-type amorphous film 31 (= p-type a-Si). Have energy. As a result, the energy band diagram of the photoelectric conversion element 10C shows that the conduction band edge of the p-type microcrystalline film 81 is the conduction of the p-type amorphous film 31 (= p-type a-Si) in the energy band diagram shown in FIG. The energy band diagram is located above the end of the band.

  Then, the photoexcited electrons and holes are efficiently recombined via the recombination level at the interface of the n-type amorphous film 21 / p-type microcrystalline film 81, and the p-type microcrystalline film 81 / i-type The internal potential of the pin junction made of the amorphous film 41 / n-type single crystal silicon (photoelectric conversion unit 51) becomes larger than that in the case where the p-type semiconductor film 3 is made of an amorphous phase. The conductivity is higher than when the p-type semiconductor film 3 is made of an amorphous phase. As a result, the conversion efficiency of the photoelectric conversion element 10C can be improved more than the conversion efficiency of the photoelectric conversion element 10A by improving the open circuit voltage Voc and the fill factor FF. In particular, the improvement of the fill factor FF is due to the decrease in series resistance due to the high conductivity of the p-type microcrystalline film 81 and the recombination of electrons and holes at the interface of the n-type amorphous film 21 / p-type microcrystalline film 81. This is due to a synergistic effect with promotion.

In addition to p-type μc-Si, p-type microcrystalline film 81 may be composed of any one of p-type μc-SiC, p-type μc-SiGe, and p-type μc-Ge as shown in Table 1. The p-type μc-SiC is formed by the above-described plasma CVD method using SiH ₄ gas, CH ₄ gas, B ₂ H ₆ gas, and H ₂ gas as material gases. The p-type μc-SiGe is formed by the above-described plasma CVD method using SiH ₄ gas, GeH ₄ gas, B ₂ H ₆ gas and H ₂ gas as material gases. The p-type μc-Ge is formed by the above-described plasma CVD method using GeH ₄ gas, B ₂ H ₆ gas, and H ₂ gas as material gases. In this case, the ratio [SiH ₄ + CH ₄ + B ₂ H ₆ ] / [H ₂ ] between the total flow rate of SiH ₄ gas, CH ₄ gas and B ₂ H ₆ gas and the flow rate of H ₂ gas is 1/10 or less. Set to Further, when p-type μc-SiGe and p-type μc-Ge are formed by the plasma CVD method, the gas flow rate ratio is similarly set.

As described above, p-type μc-SiC, p-type μc-Si, p-type μc-SiGe, and p-type μc-Ge are formed by a plasma CVD method under the condition that SiH ₄ gas or the like is diluted with H ₂ gas. Therefore, the defect density of the n-type amorphous film 21 can be increased by damage to the underlying layer (= n-type amorphous film 21) due to hydrogen ions or the like in the plasma. As a result, recombination of electrons and holes at the interface of the n-type amorphous film 21 / p-type microcrystalline film 81 can be promoted.

  In Example 3, the same change as the change from the photoelectric conversion element 10A to the photoelectric conversion element 10B may be applied to the photoelectric conversion element 10C. In this case, the photoelectric conversion unit 71 is made of p-type single crystal silicon or p-type polycrystalline silicon. The surface of p-type single crystal silicon or p-type polycrystalline silicon may have an uneven structure (texture structure).

  The other description about the photoelectric conversion element 10C is the same as the description about the photoelectric conversion element 10A.

Example 4
FIG. 6 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 4. Referring to FIG. 6, photoelectric conversion element 10D is obtained by replacing n-type amorphous film 21 of photoelectric conversion element 10A shown in FIG. 2 with n-type microcrystalline film 91, and the others are photoelectric conversion element 10A. Is the same.

  As described above, the photoelectric conversion element 10 </ b> D uses the amorphous film for the p-type semiconductor film 3 and the i-type semiconductor film 4 of the photoelectric conversion element 10 and uses the microcrystalline film for the n-type semiconductor film 2. Is embodied.

  The n-type microcrystalline film 91 is made of, for example, n-type μc-Si, and has a film thickness of, for example, 5 nm. The n-type microcrystalline film 91 is disposed between the transparent conductive film 11 and the p-type amorphous film 31 in contact with the transparent conductive film 11 and the p-type amorphous film 31.

  As described above, the photoelectric conversion element 10D includes the i-type amorphous film 41, the p-type amorphous film 31, the n-type microcrystalline film 91, the transparent conductive film 11, and the collecting electrode 9 that are connected to the photoelectric conversion unit 51 (n-type). Single-crystal silicon) is sequentially laminated on one surface, and the insulating layer 61 and the back electrode 62 are sequentially laminated on the other surface of the photoelectric conversion portion 51 (n-type single-crystal silicon).

  A method for manufacturing the photoelectric conversion element 10D will be described. Table 4 shows the flow rate of the material gas when forming the n-type microcrystalline film 91, the p-type amorphous film 31, and the i-type amorphous film 41.

  A silicon wafer made of n-type single crystal silicon as the photoelectric conversion unit 51 is cleaned by the method described above. Then, a silicon wafer (n-type single crystal silicon) is set in the plasma apparatus, and the i-type amorphous film 41 and the p-type amorphous film 31 are converted into n-type single crystal silicon using the above-described conditions by plasma CVD. It deposits sequentially on the (photoelectric conversion part 51).

Thereafter, the n-type microcrystalline film 91 is formed into a p-type amorphous film 31 / i by a plasma CVD method using ₄ sccm SiH ₄ gas, 250 sccm H ₂ gas, and hydrogen-diluted 25 sccm PH ₃ gas as material gases. Type amorphous film 41 / n-type single crystal silicon (photoelectric conversion part 51). In this case, the pressure in the reaction chamber CB3 is in the range of 13.3 Pa to 665 Pa, and the RF power is in the range of 16 to 80 mW / cm ² .

When the thickness of the n-type microcrystalline film 91 reaches 5 nm, the application of RF power to the parallel plate electrode and the supply of SiH ₄ gas, H ₂ gas and PH ₃ gas to the reaction chamber CB ₃ are stopped.

  Subsequently, the transparent conductive film 11 and the current collecting electrode 9 are sequentially stacked on the n-type microcrystalline film 91 by the method described above. Then, the insulating layer 61 and the back electrode 62 are sequentially stacked on the other surface of the n-type single crystal silicon (photoelectric conversion unit 51) by the method described above.

  Thereby, the photoelectric conversion element 10D is completed.

  The photoelectric conversion element 10 </ b> D includes an n / p junction in which the n-type microcrystalline film 91 is directly joined to the p-type amorphous film 31. Then, the n-type microcrystalline film 91 (n-type μc-Si) is in contact with the p-type amorphous film 31 (p-type a-Si) by the plasma CVD method. Deposited on Si). As a result, when the n-type microcrystalline film 91 (n-type μc-Si) is deposited, the P atoms in the n-type microcrystalline film 91 (n-type μc-Si) and the type amorphous film 31 (p-type a- B atoms in Si) diffuse to each other. Accordingly, a recombination level exists at the interface of the n-type microcrystalline film 91 / p-type amorphous film 31.

  The n / p junction composed of the n-type microcrystalline film 91 / p-type amorphous film 31 is p-type due to the recombination level at the interface of the n-type microcrystalline film 91 / p-type amorphous film 31. A decrease in internal potential of the pin junction made of the amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon (photoelectric conversion unit 51) is suppressed. Electrons and holes are efficiently recombined at the interface of the n-type microcrystalline film 91 / p-type amorphous film 31.

  Therefore, the conversion efficiency of the photoelectric conversion element 10D can be improved by improving the open circuit voltage Voc and the fill factor FF.

In addition to n-type μc-Si, n-type microcrystalline film 91 may be made of any of n-type μc-SiC, n-type μc-SiGe, and n-type μc-Ge as shown in Table 1. The n-type μc-SiC is formed by the above-described plasma CVD method using SiH ₄ gas, CH ₄ gas, PH ₃ gas, and H ₂ gas as material gases. The n-type μc-SiGe is formed by the above-described plasma CVD method using SiH ₄ gas, GeH ₄ gas, PH ₃ gas, and H ₂ gas as material gases. The n-type μc-Ge is formed by the above-described plasma CVD method using GeH ₄ gas, PH ₃ gas, and H ₂ gas as material gases. In this case, the ratio [SiH ₄ + CH ₄ + PH ₃ ] / [H ₂ ] of the total flow rate of SiH ₄ gas, CH ₄ gas and PH ₃ gas and the flow rate of H ₂ gas is set to 1/10 or less. . Further, when the n-type μc-SiGe and the n-type μc-Ge are formed by the plasma CVD method, the gas flow rate ratio is similarly set.

  In Example 4, the same change as the change from the photoelectric conversion element 10A to the photoelectric conversion element 10B may be applied to the photoelectric conversion element 10D. In this case, the photoelectric conversion unit 71 is made of p-type single crystal silicon or p-type polycrystalline silicon. The surface of p-type single crystal silicon or p-type polycrystalline silicon may have an uneven structure (texture structure).

  The other description about the photoelectric conversion element 10D is the same as the description about the photoelectric conversion element 10A.

(Example 5)
FIG. 7 is a cross-sectional view illustrating a configuration of a photoelectric conversion element in Example 5. Referring to FIG. 7, photoelectric conversion element 10E includes i-type amorphous film 101, n-type amorphous film 111, and transparent conductive film 121 as insulating layer 61 and back electrode 62 of photoelectric conversion element 10A shown in FIG. The other components are the same as those of the photoelectric conversion element 10A.

  As described above, the photoelectric conversion element 10E uses amorphous films for all of the n-type semiconductor film 2, the p-type semiconductor film 3, and the i-type semiconductor film 4 of the photoelectric conversion element 10 in the same manner as the photoelectric conversion element 10A. Thus, the photoelectric conversion element 10 is embodied.

  The i-type amorphous film 101 is made of, for example, i-type a-Si and has a film thickness of, for example, 10 nm. The i-type amorphous film 101 is in contact with the photoelectric conversion unit 51 (n-type single crystal silicon).

  The n-type amorphous film 111 is made of, for example, n-type a-Si and has a film thickness of, for example, 10 nm. The n-type amorphous film 111 is in contact with the i-type amorphous film 101.

The transparent conductive film 121 is made of, for example, SnO ₂ . The transparent conductive film 121 is in contact with the n-type amorphous film 111.

  The current collecting electrode 131 is made of, for example, Ag, and is formed in a comb shape in contact with the transparent conductive film 121.

  As described above, the photoelectric conversion element 10E has a structure in which both surfaces of the n-type single crystal silicon as the photoelectric conversion unit 51 are covered with the amorphous film.

  A method for manufacturing the photoelectric conversion element 10E will be described. The flow rate of the material gas when forming the i-type amorphous film 41, the p-type amorphous film 31, the n-type amorphous film 21, the i-type amorphous film 101, and the n-type amorphous film 111 is shown. As shown in FIG.

  A silicon wafer made of n-type single crystal silicon as the photoelectric conversion unit 51 is cleaned by the method described above, and the cleaned silicon wafer (n-type single crystal silicon) is set in a plasma apparatus. In this case, the surface of the n-type single crystal silicon may have an uneven structure (texture structure).

  Then, the i-type amorphous film 41, the p-type amorphous film 31, and the n-type amorphous film 21 are formed on one of the n-type single crystal silicon (photoelectric conversion portion 51) using the above-described conditions by plasma CVD. Laminate sequentially on the surface.

  Then, the n-type amorphous film 21 / p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon (photoelectric conversion unit 51) is taken out from the plasma device, and the n-type amorphous film 21 is removed. / P-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon (photoelectric conversion part 51) is turned over and set in the plasma apparatus.

Thereafter, when the n-type single crystal silicon (photoelectric conversion part 51) / i-type amorphous film 41 / p-type amorphous film 31 / n-type amorphous film 21 is transferred to the reaction chamber CB1, 10 sccm of SiH ₄ gases and 100 sccm of H ₂ gas are supplied to the reaction chamber CB1, the pressure in the reaction chamber CB1 is set in the range of 13.3 Pa to 665 Pa, and RF power in the range of 16 to 80 mW / cm ^{2 is} applied to the parallel plate electrodes. Apply. As a result, plasma is generated in the reaction chamber CB1, and the i-type amorphous film 101 is deposited on the other surface of the n-type single crystal silicon (photoelectric conversion unit 51).

When the thickness of the i-type amorphous film 101 reaches 10 nm, the application of RF power to the parallel plate electrode is stopped and the supply of SiH ₄ gas and H ₂ gas to the reaction chamber CB1 is stopped.

Thereafter, the i-type amorphous film 101 / n-type single crystal silicon (photoelectric conversion part 51) / i-type amorphous film 41 / p-type amorphous film 31 / n-type amorphous film 21 are transferred to the reaction chamber CB3. Transport. Then, 20 sccm of SiH ₄ gas, 150 sccm of H ₂ gas, and 50 sccm of PH ₃ gas diluted with hydrogen are supplied to the reaction chamber CB 3, and the pressure in the reaction chamber CB 3 is set in the range of 13.3 Pa to 665 Pa. An RF power in the range of 16 to 80 mW / cm ² is applied to the plate electrode. As a result, plasma is generated in the reaction chamber CB3, and the n-type amorphous film 111 is deposited on the i-type amorphous film 101.

When the thickness of the n-type amorphous film 111 reaches 10 nm, the application of RF power to the parallel plate electrode is stopped and the supply of SiH ₄ gas, H ₂ gas and PH ₃ gas to the reaction chamber CB3 is stopped. Stop.

  Thereafter, n-type amorphous film 111 / i-type amorphous film 101 / n-type single crystal silicon (photoelectric conversion part 51) / i-type amorphous film 41 / p-type amorphous film 31 / n-type amorphous film The material film 21 is taken out from the plasma apparatus and set in a sputtering apparatus.

Then, SnO ₂ as the transparent conductive film 11 and Ag as the collector electrode 9 are sequentially stacked on the n-type amorphous film 21 by the method described above.

Subsequently, SnO ₂ as the transparent conductive film 121 and Ag as the collecting electrode 131 are sequentially stacked on the n-type amorphous film 111 by the method described above.

  Thereby, the photoelectric conversion element 10E is completed.

  FIG. 8 is an energy band diagram of the photoelectric conversion element 10E shown in FIG. In FIG. 8, the collecting electrodes 9 and 131 are omitted. In FIG. 8, the internal potential of the pin junction made of p-type amorphous film 31 / i-type amorphous film 41 / n-type single crystal silicon (photoelectric conversion unit 51) is expressed as “Vbi1”, and n The internal potential of the junction formed of type single crystal silicon (photoelectric conversion portion 51) / i type amorphous film 101 / n type amorphous film 111 is denoted as “Vbi2”.

  Referring to FIG. 8, the energy band diagram of the n-type amorphous film 21, the p-type amorphous film 31, the i-type amorphous film 41, and the n-type single crystal silicon (photoelectric conversion unit 51) is shown. As described in FIG.

  Since i-type a-Si as the i-type amorphous film 101 has an optical band gap of 1.74 eV and an activation energy of 0.73 eV, n-type single crystal silicon (photoelectric conversion unit 51) / i-type non-crystalline The interface of the crystalline film 101 becomes a heterojunction. A band discontinuity exists at the interface of the n-type single crystal silicon (photoelectric conversion unit 51) / i-type amorphous film 101.

  In addition, since n-type a-Si as the n-type amorphous film 111 has an optical band gap of 1.80 eV and an activation energy of 0.20 eV, the i-type amorphous film 101 / n-type amorphous film The interface of the film 111 also becomes a heterojunction.

  An internal potential Vbi2 is generated at the junction made of n-type single crystal silicon (photoelectric conversion portion 51) / i-type amorphous film 101 / n-type amorphous film 111.

  Further, by inserting the i-type amorphous film 101 between the n-type amorphous film 111 and the n-type single crystal silicon (photoelectric conversion portion 51), the n-type amorphous film 111 / i-type amorphous film is obtained. Recombination of carriers (electrons and holes) at the interface of the mass film 101 and the interface of the i-type amorphous film 101 / n-type single crystal silicon (photoelectric conversion unit 51) is reduced.

  Then, the photoexcited electrons in the n-type single crystal silicon (photoelectric conversion unit 51) move to the i-type amorphous film 101 side by carrier diffusion, and efficiently reach the transparent conductive film 121 by the internal electric field Vbi2. Also, the photoexcited holes in the n-type single crystal silicon (photoelectric conversion unit 51) move to the i-type amorphous film 41 side by carrier diffusion, and are efficiently transferred to the p-type amorphous film 31 by the internal potential Vbi1. To reach.

  Then, the electrons reach the n-type amorphous film 21 through the collecting electrode 131, an external lead wire (not shown), the collecting electrode 9 and the transparent conductive film 11.

  Then, at the interface of the n-type amorphous film 21 / p-type amorphous film 31, electrons recombine efficiently with holes through recombination levels.

  Further, as described above, the n / p junction composed of the n-type amorphous film 21 and the p-type amorphous film 31 suppresses the decrease in the internal potential Vbi1.

  Therefore, the conversion efficiency of the photoelectric conversion element 10E can be improved by improving the open circuit voltage Voc and the fill factor FF.

  Further, the photoelectric conversion element 10E includes an i-type amorphous film 41, a p-type amorphous film 31, an n-type amorphous film 21, a transparent conductive film 11, and a collecting electrode 9 formed of n-type single crystal silicon (photoelectric conversion). The i-type amorphous film 101, the n-type amorphous film 111, the transparent conductive film 121, and the current collecting electrode 131 are stacked on one surface of the part 51) in sequence. It has a structure in which the other surface is sequentially laminated. The i-type amorphous film 41, the p-type amorphous film 31, the n-type amorphous film 21, the transparent conductive film 11, the collecting electrode 9, the i-type amorphous film 101, and the n-type amorphous film 111, the transparent conductive film 121, and the current collecting electrode 131 are formed at a temperature of 200 ° C. or lower.

  Therefore, quality deterioration of the n-type single crystal silicon (photoelectric conversion unit 51) due to thermal damage can be prevented.

  Further, the photoelectric conversion element 10E has a symmetrical structure with the n-type single crystal silicon (photoelectric conversion portion 51) as the center except for the n-type amorphous film 21. Therefore, the thermal strain applied to the n-type single crystal silicon (photoelectric conversion unit 51) is also symmetric, and the warpage of the photoelectric conversion element 10E due to the thermal strain can be prevented.

  The i-type amorphous film 101 may be made of either i-type a-SiC or i-type a-SiGe in addition to i-type a-Si. Here, the reason why i-type a-Ge is excluded is the same as described above. The n-type amorphous film 111 may be made of any of n-type a-SiC, n-type a-SiGe, and n-type a-Ge in addition to n-type a-Si.

  These i-type a-SiC, i-type a-SiGe, n-type a-SiC, n-type a-SiGe, and n-type a-Ge are formed by plasma CVD as described above.

  In Example 5, the photoelectric conversion unit 51 of the photoelectric conversion element 10E may be made of any of p-type single crystal silicon, n-type polycrystalline silicon, and p-type polycrystalline silicon. In this case, the surface of p-type single crystal silicon, n-type polycrystalline silicon, and p-type polycrystalline silicon may have an uneven structure (texture structure).

  When the photoelectric conversion unit 51 is made of n-type polycrystalline silicon or p-type polycrystalline silicon, it is preferable that after one surface of the n-type polycrystalline silicon or p-type polycrystalline silicon is subjected to plasma treatment, i-type amorphous The material film 41, the p-type amorphous film 31, the n-type amorphous film 21, the transparent conductive film 11 and the collecting electrode 9 are formed on one surface of n-type polycrystalline silicon or p-type polycrystalline silicon by plasma CVD. Then, after the other surface of the n-type polycrystalline silicon or the p-type polycrystalline silicon is subjected to plasma treatment, the i-type amorphous film 101, the n-type amorphous film 111, the transparent conductive film 121, and the collector are collected. The electric electrode 131 is sequentially laminated on the other surface of n-type polycrystalline silicon or p-type polycrystalline silicon. Thereby, the grain boundary of n-type polycrystalline silicon or p-type polycrystalline silicon can be passivated by H atoms, and recombination of carriers (electrons and holes) at the grain boundary of n-type polycrystalline silicon or p-type polycrystalline silicon can be achieved. Can be reduced.

  Further, the same change as the change from the photoelectric conversion element 10A to any one of the photoelectric conversion elements 10C and 10D may be applied to the photoelectric conversion element 10E.

  Further, in the photoelectric conversion element 10E, an n-type microcrystalline film may be applied instead of the n-type amorphous film 111. In this case, the n-type microcrystalline film is made of n-type μc-SiC, n-type μc-Si, n-type μc-SiGe, and n-type μc-Ge. The n-type μc-SiC, n-type μc-Si, n-type μc-SiGe, and n-type μc-Ge are deposited on the i-type amorphous film 101 by plasma CVD at a temperature of 200 ° C. or lower. Therefore, it is possible to prevent the quality of the photoelectric conversion unit 51 (single crystal silicon or polycrystalline silicon) from being deteriorated due to thermal damage. In addition, warpage of the photoelectric conversion element 10E due to thermal strain can be prevented.

In the above description, the P concentration of the n-type amorphous film 21 has been described as being 5 × 10 ²⁰ cm ^{−3 to} 7 × 10 ²⁰ cm ⁻³ . However, in the embodiment of the present invention, the P concentration is not limited thereto. First, the P concentration of the n-type amorphous film 21 may be lower than 5 × 10 ²⁰ cm ^{−3 to} 7 × 10 ²⁰ cm ⁻³ .

Even if the P concentration of the n-type amorphous film 21 is lower than 5 × 10 ²⁰ cm ^{−3 to} 7 × 10 ²⁰ cm ⁻³ , the n-type amorphous film 21 and the p-type amorphous film 31 (or p) This is because a recombination level is present at the interface with the type microcrystalline film 81), recombination of electrons and holes is promoted, and a decrease in internal potential Vbi is suppressed.

  The other description about the photoelectric conversion element 10E is the same as the description of the photoelectric conversion element 10A.

[Improvement of p-type semiconductor film 3]
The p-type semiconductor film 3 may be composed of a layer A made of an amorphous phase and a layer B made of a microcrystalline phase.

  The layer A is made of, for example, p-type a-Si, and the layer B is made of, for example, p-type μc-Si. The layer A is disposed on the n-type semiconductor film 2 side, and the layer B is disposed on the i-type semiconductor film 4 side.

  Thus, by forming the p-type semiconductor film 3 by the two layers A and B, the junction made of the n-type semiconductor film 2 / p-type semiconductor film 3 hardly exhibits rectification characteristics, and the layer B (= A junction made of p-type μc-Si) / i-type semiconductor film 4 / photoelectric conversion portion 5 (n-type single crystal silicon, p-type single crystal silicon, n-type polycrystalline silicon, or p-type polycrystalline silicon) is formed. Is done. As a result, recombination of electrons and holes at the interface between the n-type semiconductor film 2 and the layer A (= p-type a-Si) is promoted, and the internal potential of the junction is improved.

  Therefore, the conversion efficiency of the photoelectric conversion element 10 can be improved by improving the open circuit voltage Voc and the fill factor FF.

  Further, the sum of the film thickness of the layer A and the film thickness of the layer B may be the same as or different from the film thickness when the p-type semiconductor film 3 is a single layer. Furthermore, the film thickness of the layer A may be the same as the film thickness of the layer B, or may be different from the film thickness of the layer B.

  Even if the sum of the thickness of the layer A and the thickness of the layer B is larger than the thickness of the p-type semiconductor film 31, the light absorption coefficient of the microcrystalline film used for the layer B is amorphous. Since it is smaller than the light absorption coefficient of the material film, the intensity of sunlight incident on the photoelectric conversion unit 5 can be kept the same as the intensity when the p-type semiconductor film 3 is made of an amorphous film. As a result, if the film thickness of the layer B is set to be larger than the film thickness of the layer A, the internal potential of the junction composed of the p-type semiconductor film 3 / i-type semiconductor film 4 / photoelectric conversion unit 5 is further strengthened to increase the n-type. The recombination of electrons and holes at the interface between the semiconductor film 2 and the layer A (= p-type a-Si) can be promoted.

  Further, when the sum of the film thickness of the layer A and the film thickness of the layer B is the same as the film thickness of the p-type semiconductor film 3, the transmitted light amount of the two layers A and B is that the p-type semiconductor film 3 is amorphous. Since the number is larger than that of the material film, the short circuit current density Jsc can be increased. Thus, when the sum of the film thickness of the layer A and the film thickness of the layer B is the same as the film thickness of the p-type semiconductor film 3, the recombination of electrons and holes is promoted, and the p-type semiconductor film 3 The short-circuit current density Jsc can be increased while suppressing a decrease in the internal potential of the junction composed of / i-type semiconductor film 4 / photoelectric conversion unit 5.

  The combination of the layers A and B is (p-type a-SiC, p-type a-Si, p-type a-SiGe, p-type a-Ge, regardless of p-type a-Si / p-type μc-Si. Any) / (any of p-type μc-SiC, p-type μc-Si, p-type μc-SiGe, p-type μc-Ge).

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  The present invention is applied to a photoelectric conversion element and a stacked photoelectric conversion element including the photoelectric conversion element.

  1, 11, 121 Transparent conductive film, 2 n-type semiconductor film, 3 p-type semiconductor film, 4 i-type semiconductor film, 5, 51, 71 Photoelectric conversion part, 9, 131 Current collecting electrode, 10, 10A, 10B, 10C , 10D, 10E photoelectric conversion element, 21, 111 n-type amorphous film, 31 p-type semiconductor film, 41, 101 i-type amorphous film, 61 insulating layer, 62 back electrode, 81 p-type microcrystalline film, 91 n-type microcrystalline film.

Claims (8)

A photoelectric conversion unit made of crystalline silicon;
An i-type semiconductor film formed in contact with the photoelectric conversion unit;
A p-type semiconductor film formed in contact with the i-type semiconductor film;
An n-type semiconductor film formed in contact with the p-type semiconductor film;
A transparent conductive film formed in contact with the n-type semiconductor film,
One of the p-type semiconductor film and the n-type semiconductor film is made of an amorphous phase,
The other of the p-type semiconductor film and the n-type semiconductor film is a photoelectric conversion element made of a microcrystalline phase or an amorphous phase.   The photoelectric conversion element according to claim 1, wherein the photoelectric conversion unit is made of n-type single crystal silicon.   The photoelectric conversion element according to claim 1, wherein the photoelectric conversion unit is made of p-type single crystal silicon.   The photoelectric conversion element according to any one of claims 1 to 3, wherein the i-type semiconductor film, the p-type semiconductor film, and the n-type semiconductor film are made of an amorphous phase. The i-type semiconductor film is made of i-type amorphous silicon,
The p-type semiconductor film is made of p-type amorphous silicon,
The photoelectric conversion element according to claim 4, wherein the n-type semiconductor film is made of n-type amorphous silicon. The i-type semiconductor film is composed of an amorphous phase,
One of the p-type semiconductor film and the n-type semiconductor film is composed of an amorphous phase,
4. The photoelectric conversion element according to claim 1, wherein the other of the p-type semiconductor film and the n-type semiconductor film is made of a microcrystalline phase. 5. The i-type semiconductor film is made of i-type amorphous silicon,
The p-type semiconductor film is made of p-type microcrystalline silicon,
The photoelectric conversion element according to claim 6, wherein the n-type semiconductor film is made of n-type amorphous silicon. The i-type semiconductor film is made of i-type amorphous silicon,
The p-type semiconductor film is made of p-type amorphous silicon,
The photoelectric conversion element according to claim 6, wherein the n-type semiconductor film is made of n-type microcrystalline silicon.

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