JP2014086654A - Compound semiconductor solar cell and method of manufacturing compound semiconductor solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound semiconductor solar cell which can be improved in conversion efficiency.SOLUTION: The compound semiconductor solar cell comprises: a first photoelectric conversion cell; a second photoelectric conversion cell; and a third photoelectric conversion cell in this order. The third photoelectric conversion cell includes a first compound semiconductor layer and a second compound semiconductor layer. The band gap energy of the first compound semiconductor layer is slightly larger than that of the second compound semiconductor layer. The absolute value of a difference between the band gap energy of the first compound semiconductor layer and the band gap energy of the second compound semiconductor layer is 0.05 eV or less.

Description

  The present invention relates to a compound semiconductor solar cell and a method for producing a compound semiconductor solar cell.

  In recent years, compound semiconductor solar cells formed of III-V group compound semiconductors (see, for example, Patent Document 1) have been used for space use or light collection, taking advantage of their high conversion efficiency.

  FIG. 10 shows a schematic cross-sectional view of a conventional three-junction compound semiconductor solar cell. A conventional three-junction compound semiconductor solar cell shown in FIG. 10 has an n-type Ge layer 102, an n-type InGaP nucleation layer 103 (thickness 0.02 μm), and an n-type InGaAs buffer layer 104 on a p-type Ge substrate 101. (Thickness 0.08 μm), n ++ type GaAs layer 105 (thickness 0.02 μm), p ++ type GaAs layer 106 (thickness 0.02 μm), B + layer 107 (thickness) made of p + type InGaP 0.1 μm), p-type InGaAs layer 108 (thickness 3 μm), n-type InGaAs layer 109 (thickness 0.1 μm), n-type InGaP window layer 110 (thickness 0.01 μm), n ++-type InGaP layer 111 (Thickness 0.02 μm), p ++ type AlGaAs layer 112 (thickness 0.02 μm), base layer 113 (thickness 0.1 μm) made of p + type AlInP, p type InGaP layer 114 (thickness 0. 7 μm), n-type InGaP A layer 115 (thickness 0.05 μm), an n-type AlInP window layer 116 (thickness 0.03 μm), and an n-type GaAs layer 117 (thickness 0.5 μm) are sequentially stacked.

  An upper electrode 202 is provided on the surface of the n-type GaAs layer 117, and a lower electrode 201 is provided on the back surface of the p-type Ge substrate 101. An antireflection film 203 is formed on the surface of the n-type AlInP window layer 116 where the n-type GaAs layer 117 is not formed.

  The n-type Ge layer 102 is formed by the diffusion of phosphorus atoms from the n-type InGaP nucleation layer 103, and the thickness of the n-type Ge layer 102 is about 0.1 μm. A bottom cell 10 is formed from the p-type Ge substrate 101 and the n-type Ge layer 102.

  A tunnel junction layer 40a is formed from the n ++ type GaAs layer 105 and the p ++ type GaAs layer 106.

  A middle cell 20 is formed from the p-type InGaAs layer 108 and the n-type InGaAs layer 109.

  A tunnel junction layer 40b is formed from the n ++ type InGaP window layer 111 and the p ++ type AlGaAs layer 112.

  A top cell 30 is formed from the p-type InGaP layer 114 and the n-type InGaP layer 115.

  When the conventional three-junction compound semiconductor solar cell shown in FIG. 10 is designed for condensing, that is, when the thickness and carrier concentration of each layer are optimally designed to be optimal for the AM1.5 solar spectrum. Shows a conversion efficiency of 31% at 1 SUN and a conversion efficiency of about 40% at 1000 times condensing.

  FIG. 11 shows the spectral sensitivity characteristics of the conventional three-junction compound semiconductor solar cell shown in FIG. According to the spectral sensitivity characteristic shown in FIG. 11, under the AM1.5 sunlight spectrum at the time of condensing, the ratio of the amount of current that can be generated in the top cell 30, middle cell 20, and bottom cell 10 is 1.01 respectively. Therefore, the current amount of the conventional three-junction compound semiconductor solar battery shown in FIG. 10 is limited by the amount of current generated in the middle cell 20.

  Therefore, as a technique for increasing the amount of current that can be generated in the middle cell, for example, in Non-Patent Document 1, by inserting an InAs quantum dot layer or a GaAsP / InGaAs quantum well layer into a middle cell composed of a GaAs layer, Attempts have been made to increase the quantum efficiency on the long wavelength side. According to this, the amount of current that can be generated in the middle cell of the conventional three-junction compound semiconductor solar battery shown in FIG. 10 can be increased by about 3%.

JP 2000-312017 A

Yunpeng Wang et al., “A Superlattice Solar Cell With Enhanced Short-Circuit Current and Minimized Drop in Open-Circuit Voltage”, IEEE JOURNAL OF PHOTOVOLTAICS, VOL.2, No.3, JULY 2012, pp.387 to 392

  However, in the conventional three-junction compound semiconductor solar battery shown in FIG. 10 manufactured by introducing the method described in Non-Patent Document 1, the amount of current that can be generated in the top cell 30, the middle cell 20, and the bottom cell 10 The ratios are about 1.01, 1.03, and 1.67, respectively, and the current amount of the conventional three-junction compound semiconductor solar cell shown in FIG. 10 is now limited by the amount of current generated in the top cell 30. It will be. Further, when the quantum efficiency on the long wavelength side of the middle cell 20 is increased by introducing the method described in Non-Patent Document 1, the open-circuit voltage of the middle cell 20 is slightly decreased at the same time. The conversion efficiency of the entire solar cell is about 40.2% at 1000 times condensing, and only increases by about 0.2%.

  In view of said situation, the objective of this invention is providing the manufacturing method of the compound semiconductor solar cell which can improve conversion efficiency, and a compound semiconductor solar cell.

  The present invention includes a first photoelectric conversion cell, a second photoelectric conversion cell provided on the first photoelectric conversion cell, and a third photoelectric conversion cell provided on the second photoelectric conversion cell. And the third photoelectric conversion cell includes a first compound semiconductor layer and a second compound semiconductor layer, and the band gap energy of the first compound semiconductor layer is the band gap energy of the second compound semiconductor layer. And a compound semiconductor solar cell in which the absolute value of the difference between the band gap energy of the first compound semiconductor layer and the band gap energy of the second compound semiconductor layer is 0.05 eV or less. By setting it as such a structure, the compound semiconductor solar cell with improved conversion efficiency can be obtained.

  In the present invention, the first photoelectric conversion is performed by forming the n-type Ge layer after forming the n-type InGaP nucleation layer on the (100) plane of the p-type Ge substrate having an off angle of 2 ° or less. Forming a cell, and forming a second photoelectric conversion cell including a base layer including a third compound semiconductor layer and a fourth compound semiconductor layer having different band gap energies on the first photoelectric conversion cell. And forming a third photoelectric conversion cell including a base layer composed of a first compound semiconductor layer and a second compound semiconductor layer having different band gap energies on the second photoelectric conversion cell. The first compound semiconductor layer is an InGaP layer to which Sb is added, and the second compound semiconductor layer is a method for manufacturing a compound semiconductor solar cell that is an InGaP layer to which Sb is not added. By setting it as such a structure, the spectral sensitivity by the side of the long wavelength of a 3rd photoelectric conversion cell can be increased, and the short circuit current amount of the compound semiconductor solar cell of this invention can be increased.

  Furthermore, the present invention provides a base layer comprising a first compound semiconductor layer and a second compound semiconductor layer having different band gap energies on the (100) plane of a p-type GaAs substrate having an off angle of 2 ° or less. A second photoelectric conversion cell including a base layer made of a third compound semiconductor layer and a fourth compound semiconductor layer having different band gap energies on the third photoelectric conversion cell. And a step of forming the first photoelectric conversion cell on the second photoelectric conversion cell, wherein the first compound semiconductor layer is an InGaP layer to which Sb is added, In this method, the second compound semiconductor layer is an InGaP layer to which Sb is not added. By setting it as such a structure, the spectral sensitivity by the side of the long wavelength of a 3rd photoelectric conversion cell can be increased, and the short circuit current amount of the compound semiconductor solar cell of this invention can be increased.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the compound semiconductor solar cell which can improve conversion efficiency, and a compound semiconductor solar cell can be provided.

1 is a schematic cross-sectional view of a compound semiconductor solar battery according to Embodiment 1. FIG. It is a figure which shows the spectral sensitivity characteristic of the compound semiconductor solar cell of Embodiment 1. FIG. 6 is a schematic cross-sectional view of a compound semiconductor solar battery according to Embodiment 2. FIG. It is a figure which shows the spectral sensitivity characteristic of the compound semiconductor solar cell of Embodiment 2. FIG. It is a figure which shows the electric current increase rate of the top cell in the compound semiconductor solar cell of Embodiment 2, and the relationship between the off angle of a Ge board | substrate. 4 is a schematic cross-sectional view of a compound semiconductor solar battery according to Embodiment 3. FIG. 12 is a schematic cross-sectional view illustrating a manufacturing process of an example of a method for manufacturing the compound semiconductor solar battery of Embodiment 3. FIG. 12 is a schematic cross-sectional view illustrating a manufacturing process of an example of a method for manufacturing the compound semiconductor solar battery of Embodiment 3. FIG. It is a figure which shows the spectral sensitivity characteristic of the compound semiconductor solar cell of Embodiment 3. It is typical sectional drawing of the conventional 3 junction type compound semiconductor solar cell. It is a figure which shows the spectral sensitivity characteristic of the conventional 3 junction type compound semiconductor solar cell shown in FIG.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

  The compound semiconductor solar battery of the present invention includes a first photoelectric conversion cell, a second photoelectric conversion cell provided on the first photoelectric conversion cell, and a third photoelectric conversion cell provided on the second photoelectric conversion cell. The third photoelectric conversion cell includes a first compound semiconductor layer and a second compound semiconductor layer, and the band gap energy of the first compound semiconductor layer is the second compound semiconductor. The absolute value of the difference between the band gap energy of the first compound semiconductor layer and the band gap energy of the second compound semiconductor layer is slightly larger than the band gap energy of the layer. The compound semiconductor solar cell of the present invention having such a configuration has improved conversion efficiency as will be demonstrated in the embodiments described later.

  In the compound semiconductor solar battery of the present invention, the second photoelectric conversion cell includes a third compound semiconductor layer and a fourth compound semiconductor layer, and the band gap energy of the third compound semiconductor layer is the first 4 is slightly larger than the band gap energy of the compound semiconductor layer 4, and the absolute value of the difference between the band gap energy of the third compound semiconductor layer and the band gap energy of the fourth compound semiconductor layer is 0.05 eV or less. Is preferred. Also in this case, the conversion efficiency of the compound semiconductor solar cell of the present invention is improved.

  In the compound semiconductor solar battery of the present invention, the band gap energy of the semiconductor constituting the first photoelectric conversion cell is preferably 1.1 eV or less, and more preferably 1.05 eV or less. When the band gap energy of the semiconductor constituting the first photoelectric conversion cell is 1.1 eV or less, particularly when it is 1.05 eV or less, the amount of short-circuit current of the compound semiconductor solar battery of the present invention tends to increase. is there.

  The semiconductor constituting the first photoelectric conversion cell is not particularly limited, and examples thereof include semiconductors such as InGaAs, InGaAlAs, InGaAsN, and InGaAlAsN. Among them, it is preferable to use InGaAs as the semiconductor constituting the first photoelectric conversion cell because the number of constituent elements is the smallest and the material supply at the time of formation is easily controlled. Here, when InGaAs is used as the compound semiconductor constituting the first photoelectric conversion cell, In (indium) is used so that the band gap energy of the compound semiconductor constituting the first photoelectric conversion cell is 1.1 eV or less. ) And Ga (gallium) composition ratio can be set as appropriate. When a semiconductor that does not lattice match with a GaAs substrate and a Ge substrate, such as InGaAs, is used as a semiconductor constituting the first photoelectric conversion cell, a buffer layer that relaxes lattice mismatch is formed on these substrates. It is preferable that the first photoelectric conversion cell is formed. Further, Ge can also be used as the semiconductor constituting the first photoelectric conversion cell of the present invention, and in this case, the band gap energy of the semiconductor constituting the first photoelectric conversion cell is about 0.67 eV. In addition, the semiconductor which comprises a 1st photoelectric conversion cell can be formed by MOCVD (Metal Organic Chemical Vapor Deposition) method etc., for example.

  The thickness of the first photoelectric conversion cell is not particularly limited, but is preferably 1.5 μm or more and 4.5 μm or less, and more preferably 2 μm or more and 4 μm or less. When the thickness of the first photoelectric conversion cell is 1.5 μm or more, particularly when it is 2 μm or more, the short-circuit current amount of the compound semiconductor solar battery of the present invention tends to increase. When the thickness of the first photoelectric conversion cell is 4.5 μm or less, particularly when it is 4 μm or less, the open circuit voltage of the compound semiconductor solar battery of the present invention tends to increase.

  In addition, the third compound semiconductor layer included in the second photoelectric conversion cell is not particularly limited, and examples thereof include GaAs, InGaAs, AlGaAs, and InGaAlAs. Among these, since the number of constituent elements is small and the supply of materials at the time of formation is easy to control, and because it is a compound semiconductor lattice-matched to a GaAs substrate and a Ge substrate, the third compound semiconductor layer is It is preferable to use GaAs or InGaAs. Here, when InGaAs is used as the third compound semiconductor layer, the composition ratio of In and Ga can be set as appropriate so as to lattice match with the Ge substrate. In addition, the second photoelectric conversion cell includes a fourth compound semiconductor layer having a band gap slightly lower than the band gap of the third compound semiconductor layer (the band gap energy of the third compound semiconductor layer and the fourth compound semiconductor layer). By introducing an InAs quantum dot-added layer and / or an InGaAs / GaAsP quantum well layer, etc., the absolute value of the difference from the band gap energy of the second photoelectric conversion cell is It is also possible to increase the quantum efficiency on the long wavelength side. Note that the third compound semiconductor layer and the fourth compound semiconductor layer included in the second semiconductor photoelectric conversion cell can be formed by, for example, the MOCVD method.

  The thickness of the second photoelectric conversion cell is not particularly limited, but is preferably 1.5 μm or more and 4.5 μm or less, and preferably 2 μm or more and 4 μm or less. When the thickness of the second photoelectric conversion cell is 1.5 μm or more, particularly when the thickness is 2 μm or more, the short-circuit current amount of the compound semiconductor solar battery of the present invention tends to increase. When the thickness of the second photoelectric conversion cell is 4.5 μm or less, particularly when it is 4 μm or less, the open circuit voltage of the compound semiconductor solar battery of the present invention tends to increase.

  In addition, the first compound semiconductor layer included in the third photoelectric conversion cell is not particularly limited, and examples thereof include InGaP, AlInGaP, InGaN, and AlInGaN. Especially, it is preferable to use InGaP or AlInGaP as the first compound semiconductor layer because it is a compound semiconductor that easily grows crystals. Here, when AlInGaP is used as the first compound semiconductor layer, the composition ratio of Al, In, and Ga can be appropriately set so as to lattice match with a semiconductor substrate such as GaAs. In this case, the third photoelectric conversion cell also includes a second compound semiconductor layer having a band gap slightly lower than the band gap of the first compound semiconductor layer (the band gap energy of the first compound semiconductor layer and the first compound semiconductor layer). It is possible to increase the quantum efficiency on the long wavelength side of the third photoelectric conversion cell by introducing an InGaP layer or the like as the absolute value of the difference from the band gap energy of the compound semiconductor layer 2 is 0.05 eV or less) It is. An InGaP layer to which Sb is added is used as the first compound semiconductor layer, and the composition ratio of In and Ga can be set as appropriate so as to lattice match with a semiconductor substrate such as GaAs. In this case, the second compound semiconductor layer having a band gap slightly lower than the band gap of the first compound semiconductor layer (the difference between the band gap energy of the first compound semiconductor layer and the band gap energy of the second compound semiconductor layer). It is also possible to increase the quantum efficiency on the long wavelength side of the third photoelectric conversion cell by introducing an InGaP layer to which Sb is not added into the third photoelectric conversion cell, with an absolute value of 0.05 eV or less) is there.

  The thickness of the third photoelectric conversion cell is not particularly limited, but is preferably 0.5 μm or more and 2 μm or less, and more preferably 0.7 μm or more and 1.5 μm or less. When the thickness of the third photoelectric conversion cell is 0.5 μm or more, particularly when the thickness is 0.7 μm or more, the short-circuit current amount of the compound semiconductor solar battery of the present invention tends to increase. Moreover, when the thickness of the third photoelectric conversion cell is 2 μm or less, particularly when it is 1.5 μm or less, the open-circuit voltage of the compound semiconductor solar battery of the present invention tends to increase.

  The thickness of the second compound semiconductor layer of the third photoelectric conversion cell is preferably 0.01 μm or more and 0.1 μm or less. When the thickness of the second compound semiconductor layer of the third photoelectric conversion cell is 0.01 μm or more and 0.1 μm or less, the decrease in the open-circuit voltage of the compound semiconductor solar battery of the present invention is reduced, and the short circuit current The amount tends to increase.

  In the first aspect of the method for producing a compound semiconductor solar battery of the present invention, an n-type InGaP nucleation layer is formed on the (100) plane of a p-type Ge substrate having an off angle of 2 ° or less, and then n-type. A step of forming a first photoelectric conversion cell by forming a Ge layer, and a base composed of a third compound semiconductor layer and a fourth compound semiconductor layer having different band gap energies on the first photoelectric conversion cell Forming a second photoelectric conversion cell including a layer; and a first layer including a base layer including a first compound semiconductor layer and a second compound semiconductor layer having different band gap energies on the second photoelectric conversion cell. Forming a third photoelectric conversion cell, wherein the first compound semiconductor layer of the third photoelectric conversion cell is an InGaP layer to which Sb is added, and the second compound semiconductor layer of the third photoelectric conversion cell is S It has been with the InGaP layer but not added. Thus, the third photoelectric conversion cell is formed only from the InGaP layer to which no Sb is added by setting the band gap energy of the first compound semiconductor layer slightly larger than the band gap energy of the second compound semiconductor layer. Compared with the case where it is manufactured, the spectral sensitivity on the long wavelength side of the third photoelectric conversion cell can be increased, and the amount of short-circuit current of the compound semiconductor solar battery can be increased.

  In the second aspect of the method for producing a compound semiconductor solar cell of the present invention, first compound semiconductor layers having different band gap energies on the (100) plane of a p-type GaAs substrate provided with an off angle of 2 ° or less. Forming a third photoelectric conversion cell including a base layer composed of a first compound semiconductor layer and a third compound semiconductor layer, a third compound semiconductor layer having a different band gap energy on the third photoelectric conversion cell, and a fourth A step of forming a second photoelectric conversion cell including a base layer composed of a compound semiconductor layer and a step of forming a first photoelectric conversion cell on the second photoelectric conversion cell; The first compound semiconductor layer of the cell is an InGaP layer to which Sb is added, and the second compound semiconductor layer of the third photoelectric conversion cell is an InGaP layer to which Sb is not added. Thus, the third photoelectric conversion cell is formed only from the InGaP layer to which no Sb is added by setting the band gap energy of the first compound semiconductor layer slightly larger than the band gap energy of the second compound semiconductor layer. Compared with the case where it is manufactured, the spectral sensitivity on the long wavelength side of the third photoelectric conversion cell can be increased, and the amount of short-circuit current of the compound semiconductor solar battery can be increased.

  FIG. 1 is a schematic cross-sectional view of the compound semiconductor solar battery of Embodiment 1 which is an example of the compound semiconductor solar battery of the present invention. Compared with the conventional three-junction compound semiconductor solar cell shown in FIG. 10, the compound semiconductor solar cell of the first embodiment has a p-type InGaAs / layer below the p-type InGaAs base layer 108 (thickness 3 μm) of the middle cell 20. The point where the GaAsP quantum well layer 108a is formed, and the emitter layer of the top cell 30 is formed of an n-type AlGaInP layer 115a (thickness 0.05 μm; composition ratio of Al to the whole group III atoms 0.05), The base layer of the top cell 30 includes two layers of a p-type AlGaInP layer 114a (thickness 2.5 μm; a composition ratio of Al with respect to the entire group III atoms 0.05) and a p-type InGaP layer 114b (thickness 0.1 μm). It differs in that it is formed. Note that the absolute value of the difference between the band gap energy of the p-type AlGaInP layer 114a of the top cell 30 and the band gap energy of the p-type InGaP layer 114b is 0.05 eV or less. The absolute value of the difference between the band gap energy of the p-type InGaAs base layer 108 of the middle cell 20 and the band gap energy of the p-type InGaAs / GaAsP quantum well layer 108a is 0.05 eV or less.

  FIG. 2 shows the spectral sensitivity characteristics of the compound semiconductor solar cell of the first embodiment shown in FIG. The spectral sensitivity characteristic of the compound semiconductor solar cell of the first embodiment shown in FIG. 2 is shorter than the spectral sensitivity characteristic of the conventional three-junction compound semiconductor solar cell shown in FIG. The difference is that the sensitivity characteristic is improved in a shoulder shape on the long wavelength side of the top cell 30 and the middle cell 20 and the characteristic on the short wavelength side of the bottom cell 10 is deteriorated.

  According to the spectral sensitivity characteristic shown in FIG. 2, the current that can be generated in the top cell 30, middle cell 20, and bottom cell 10 of the compound semiconductor solar battery of the first embodiment under the AM1.5 sunlight spectrum at the time of condensing. The quantity ratios are about 1.04, 1.03 and 1.67, respectively. Therefore, in the compound semiconductor solar cell of the first embodiment, an increase in the short-circuit current amount of about 3% is expected as compared with the conventional three-junction compound semiconductor solar cell shown in FIG.

  Moreover, in the compound semiconductor solar cell of Embodiment 1, the conversion efficiency of 41.0% was shown at the time of 1000 times condensing. This value does not reach 41.2%, which is the conversion efficiency that can be expected when the short-circuit current amount is increased by 3% from the conversion efficiency of 40.0% of the conventional three-junction compound semiconductor solar cell shown in FIG. This is presumably because the open circuit voltage of the compound semiconductor solar battery of Embodiment 1 was slightly reduced.

  FIG. 3 shows a schematic cross-sectional view of the compound semiconductor solar battery of Embodiment 2, which is another example of the compound semiconductor solar battery of the present invention. Compared with the conventional three-junction compound semiconductor solar cell shown in FIG. 10, the compound semiconductor solar cell of the second embodiment has InAs quantum dots under the p-type InGaAs base layer 108 (thickness 3 μm) of the middle cell 20. The added p-type GaAs base layer 108b is formed, and the emitter layer of the top cell 30 is formed of an n-type InGaP emitter layer 115b (thickness 0.05 μm) to which Sb is added. The p-type InGaP base layer 114c (thickness 0.7 μm) to which Sb is added and the p-type InGaP base layer 114d (thickness 0.1 μm) to which Sb is not added are formed. Is different. In addition, the compound semiconductor solar battery according to the second embodiment uses a Ge substrate 101 having a (100) plane with no off-angle. The absolute value of the difference between the band gap energy of the p-type InGaP base layer 114c to which Sb of the top cell 30 is added and the band gap energy of the p-type InGaP base layer 114d to which Sb is not added is 0.05 eV or less. is there. The absolute value of the difference between the band gap energy of the p-type InGaAs base layer 108 of the middle cell 20 and the band gap energy of the p-type GaAs base layer 108b to which InAs quantum dots are added is 0.05 eV or less.

  FIG. 4 shows the spectral sensitivity characteristics of the compound semiconductor solar battery of the second embodiment shown in FIG. The spectral sensitivity characteristics of the compound semiconductor solar cell of the second embodiment shown in FIG. 3 are longer wavelengths of the top cell 30 and the middle cell 20 than the spectral sensitivity characteristics of the conventional three-junction compound semiconductor solar cell shown in FIG. The difference is that the sensitivity characteristic is improved in a shoulder shape on the side, and the characteristic on the short wavelength side of the bottom cell 10 is deteriorated.

  According to the spectral sensitivity characteristics shown in FIG. 4, the currents that can be generated in the top cell 30, middle cell 20, and bottom cell 10 of the compound semiconductor solar battery of the second embodiment under the AM1.5 sunlight spectrum at the time of condensing. The quantity ratios are about 1.04, 1.02, and 1.67, respectively. Therefore, in the compound semiconductor solar battery of Embodiment 2, an increase in the amount of short circuit current of about 2% is expected as compared with the conventional three-junction compound semiconductor solar battery shown in FIG.

  Moreover, in the compound semiconductor solar cell of Embodiment 2, the conversion efficiency of 40.6% was shown at the time of 1000 times condensing. This value does not reach 40.8%, which is the conversion efficiency that can be expected when the short-circuit current amount is increased by 2% from the conversion efficiency of 40.0% of the conventional three-junction compound semiconductor solar cell shown in FIG. This is presumably because the open circuit voltage of the compound semiconductor solar battery of Embodiment 2 was slightly reduced.

  As shown in FIG. 4, it can be seen that the sensitivity on the long wavelength side in the spectral sensitivity of the top cell 30 is a contribution from the p-type InGaP base layer 114d to which Sb is not added. This was confirmed by the disappearance of the sensitivity on the long wavelength side of the top cell 30 seen in FIG. 4 when the p-type InGaP base layer of the top cell 30 was formed only by adding Sb. Is due to. When Sb is added to the p-type InGaP base layer, the formation of the natural superlattice is suppressed, so that the band gap of the top cell 30 can take a crystallographically predicted value. When Sb is not added, a natural superlattice is formed, so the band gap is considered to be small.

  Although the current increase rate of the top cell 30 due to the sensitivity on the long wavelength side was about 4%, when the off rate of the Ge substrate 101 was changed, the current increase rate was examined, as shown in FIG. Results were obtained. That is, when the off angle of the Ge substrate 101 is larger than 2 °, the current increase rate of the top cell 30 is lowered. For example, when the Ge substrate 101 is provided with an off angle of 5 °, the current increase rate of the top cell 30 is zero. This corresponds to the fact that the sensitivity on the long wavelength side was not observed in the spectral sensitivity characteristics at this time. Even when the p-type InGaP base layer to which Sb is not added is increased as the off-angle of the Ge substrate 101 is increased, it is natural. This is thought to be due to the difficulty of forming a superlattice.

  FIG. 6 shows a schematic cross-sectional view of a compound semiconductor solar battery according to Embodiment 3, which is another example of the compound semiconductor solar battery of the present invention. Compared with the compound semiconductor solar cell of the second embodiment, the compound semiconductor solar cell of the third embodiment mainly includes InGaAs (band gap 1) in which the bottom cell 10 has a lattice mismatch rate of about 2% with respect to GaAs. 0.0 eV), an InGaP buffer layer 50 that gradually relaxes the lattice mismatch is formed between the bottom cell 10 and the middle cell 20, and the middle cell 20 includes an n-type GaAs emitter layer 309, p It is different in that it is formed of a p-type GaAs base layer 108b to which a p-type GaAs base layer 308 and InAs quantum dots are added. The absolute value of the difference between the band gap energy of the p-type InGaP base layer 114c to which Sb of the top cell 30 is added and the band gap energy of the p-type InGaP base layer 114d to which Sb is not added is 0.05 eV or less. is there. The absolute value of the difference between the band gap energy of the p-type GaAs base layer 308 of the middle cell 20 and the band gap energy of the p-type GaAs base layer 108b to which InAs quantum dots are added is 0.05 eV or less.

  The compound semiconductor solar cell of Embodiment 3 shown in FIG. 6 is manufactured as follows, for example. First, as shown in the schematic cross-sectional view of FIG. 7, a GaAs substrate 130 having a (100) surface with a diameter of 50 mm and no off-angle is placed in an MOCVD apparatus.

  Next, an etching stop layer 131 made of n-type InGaP capable of selective etching with GaAs, an n-type GaAs contact layer 117 and an n-type AlInP window layer 116 are grown on the GaAs substrate 130.

  Next, on the n-type AlInP window layer 116, an n-type InGaP emitter layer 115b to which Sb is added, a p-type InGaP base layer 114c to which Sb is added, a p-type InGaP base layer 114d to which Sb is not added, and p A BSF layer 113 made of + -type AlInP is epitaxially grown in this order by the MOCVD method. Thus, the top cell 30 is formed from the n-type InGaP emitter layer 115b, the p-type InGaP base layer 114c to which Sb is added, and the p-type InGaP base layer 114d to which Sb is not added.

  Next, a p ++ type AlGaAs layer 112 and an n ++ type InGaP layer 111 are epitaxially grown in this order on the BSF layer 113 made of p + type AlInP by MOCVD. Thus, the tunnel junction layer 40b is formed from the p ++ type AlGaAs layer 112 and the n ++ type InGaP layer 111.

  Next, on the n ++ type InGaP layer 111, an n type InGaP window layer 110, an n type GaAs emitter layer 309, a p type GaAs base layer 308, a p type GaAs base layer 108b doped with InAs quantum dots, and p + A BSF layer 107 made of type InGaP is epitaxially grown in this order by MOCVD. Thus, the middle cell 20 is formed from the n-type GaAs emitter layer 309, the p-type GaAs base layer 308, and the p-type GaAs base layer 108b to which InAs quantum dots are added.

  Next, a p ++ type AlGaAs layer 306 and an n ++ type InGaP layer 305 are epitaxially grown in this order by MOCVD on the BSF layer 107 made of p + type InGaP. As a result, a tunnel junction layer 41a is formed from the p ++ type AlGaAs layer 306 and the n ++ type InGaP layer 305.

Next, an n + type In _0.48 Ga _0.52 P layer 51, an n type In _0.51 Ga _0.49 P layer 52, an n type In _0.55 Ga _0.45 P layer 53, and an n type In _0.59 Ga _{0.41 are formed} on the n ++ type InGaP layer 305. P layer 54, n-type In _0.63 Ga _0.37 P layer 55, n-type In _0.67 Ga _0.33 P layer 56, n-type In _0.71 Ga _0.29 P layer 57, n-type In _0.75 Ga _0.25 P layer 58, n-type In _0.79 Ga _0.21 The P layer 59 and the n-type In _0.82 Ga _0.18 P layer 60 are epitaxially grown in this order by the MOCVD method. These layers form a buffer layer 50 for relaxing about 2% of lattice mismatch between the middle cell 20 and the next grown bottom cell 10.

Next, an n-type InGaP window layer 304, an n-type InGaAs emitter layer 303, a p-type InGaAs base layer 302, a BSF layer 301 made of p-type InGaP, and a p-type InGaAs contact layer on the n-type In _0.82 Ga _0.18 P layer 30. 300 are epitaxially grown in this order by the MOCVD method. Thereby, the bottom cell 10 is formed from the n-type InGaAs emitter layer 303 and the p-type InGaAs base layer 302.

Here, AsH ₃ (arsine) and TMG (trimethylgallium) are used for the formation of GaAs, TMI (trimethylindium), TMG and PH ₃ (phosphine) are used for the formation of InGaP, and TMI, Using TMG and AsH ₃ , TMA (trimethylaluminum), TMI and PH ₃ can be used to form AlInP, and TMA, TMG and AsH ₃ can be used to form AlGaAs.

  Thereafter, a support substrate 211 is attached on the surface of the p-type InGaAs contact layer 300 by a metal layer 210 made of a laminate of, for example, Au (for example, thickness 0.1 μm) / Ag (for example, thickness 3 μm).

  Next, as shown in the schematic cross-sectional view of FIG. 8, after etching the GaAs substrate 130 with an alkaline aqueous solution, the etching stop layer 131 made of n-type InGaP is etched with an aqueous acid solution.

  Next, after forming a resist pattern on the n-type GaAs contact layer 117 by photolithography, a part of the n-type GaAs contact layer 117 is removed by etching using an alkaline aqueous solution. Then, a resist pattern is formed again on the surface of the remaining n-type GaAs contact layer 117 by photolithography, and using a resistance heating vapor deposition apparatus and an EB (Electron Beam) vapor deposition apparatus, as shown in FIG. Upper electrode 202 made of a laminate of (12%) (for example, thickness 0.1 μm) / Ni (for example, thickness 0.02 μm) / Au (for example, thickness 0.1 μm) / Ag (for example, thickness 5 μm) is formed. Then, a similar lower electrode 201 is formed also on the support substrate 211.

Next, after a mesa etching pattern is formed, mesa etching is performed using an alkaline aqueous solution and an acid solution. Then, an antireflection film 203 is formed by forming a laminated body of, for example, a TiO ₂ film (for example, a thickness of 55 nm) and an Al ₂ O ₃ film (for example, a thickness of 85 nm) by EB vapor deposition. Thereby, the compound semiconductor solar cell of Embodiment 3 in which the light-receiving surface of the compound semiconductor solar cell is located on the side opposite to the growth direction of the compound semiconductor can be obtained.

  FIG. 9 shows the spectral sensitivity characteristics of the compound semiconductor solar battery of Embodiment 3 shown in FIG. The spectral sensitivity characteristics of the compound semiconductor solar cell of the third embodiment are such that the absorption edge of the bottom cell 10 is 1350 nm compared to the spectral sensitivity characteristics of the compound semiconductor solar cells of the first and second embodiments shown in FIGS. There are different points in the vicinity.

  According to the spectral sensitivity characteristics shown in FIG. 9, the currents that can be generated in the top cell 30, the middle cell 20, and the bottom cell 10 of the compound semiconductor solar battery of the third embodiment under the AM1.5 sunlight spectrum at the time of condensing. The ratio of the amounts is about 1.04, 1.02, and 1.03, respectively, and the current amount is matched between these cells. Therefore, compared with the conventional three-junction compound semiconductor solar cell shown in FIG. Thus, an increase in the short-circuit current amount of about 2% and an increase in the open circuit voltage of about 0.33V are expected.

  Moreover, in the compound semiconductor solar cell of Embodiment 3, the conversion efficiency of 43.5% was shown at the time of 1000 times condensing.

  As described above, according to the compound semiconductor solar battery of the present invention, since the amount of current that can be generated in the top cell can be increased, the conversion efficiency at the time of condensing can be improved.

  The present invention includes a first photoelectric conversion cell, a second photoelectric conversion cell provided on the first photoelectric conversion cell, and a third photoelectric conversion cell provided on the second photoelectric conversion cell. And the third photoelectric conversion cell includes a first compound semiconductor layer and a second compound semiconductor layer, and the band gap energy of the first compound semiconductor layer is the band gap energy of the second compound semiconductor layer. And a compound semiconductor solar cell in which the absolute value of the difference between the band gap energy of the first compound semiconductor layer and the band gap energy of the second compound semiconductor layer is 0.05 eV or less. By setting it as such a structure, the compound semiconductor solar cell with improved conversion efficiency can be obtained.

  Here, in the compound semiconductor solar battery of the present invention, it is preferable that the first compound semiconductor layer is an AlInGaP layer and the second compound semiconductor layer is an InGaP layer. With such a configuration, the quantum efficiency on the long wavelength side of the third photoelectric conversion cell can be increased.

  In the compound semiconductor solar battery of the present invention, the first compound semiconductor layer is an InGaP layer to which Sb (antimony) is added, and the second compound semiconductor layer is an InGaP layer to which Sb is not added. Is preferred. With such a configuration, the quantum efficiency on the long wavelength side of the third photoelectric conversion cell can be increased.

  Moreover, in the compound semiconductor solar battery of this invention, it is preferable that the thickness of a 2nd compound semiconductor layer is 0.01 micrometer or more and 0.1 micrometer or less. By setting it as such a structure, while the fall of the open circuit voltage of the compound semiconductor solar cell of this invention can be decreased, the amount of short circuit currents can be enlarged.

  In the compound semiconductor solar battery of the present invention, the second photoelectric conversion cell includes a third compound semiconductor layer and a fourth compound semiconductor layer, and the band gap energy of the third compound semiconductor layer is the first The absolute value of the difference between the band gap energy of the third compound semiconductor layer and the band gap energy of the fourth compound semiconductor layer is preferably 0.05 eV or less. . With such a configuration, the quantum efficiency on the long wavelength side of the second photoelectric conversion cell can be increased.

  In the compound semiconductor solar battery of the present invention, the third compound semiconductor layer is a GaAs layer or an InGaAs layer, and the fourth compound semiconductor layer is an InGaAs / GaAsP quantum well layer or a GaAs layer to which InAs quantum dots are added. It is preferable that With such a configuration, the quantum efficiency on the long wavelength side of the second photoelectric conversion cell can be increased.

  Moreover, in the compound semiconductor solar battery of this invention, it is preferable that the band gap energy of the semiconductor which comprises a 1st photoelectric conversion cell is 1.1 eV or less. By setting it as such a structure, it exists in the tendency for the short circuit current amount of the compound semiconductor solar cell of this invention to become large.

  In the compound semiconductor solar battery of the present invention, the semiconductor constituting the first photoelectric conversion cell is preferably Ge or InGaAs. By setting it as such a structure, since the band gap energy of the semiconductor which comprises a 1st photoelectric conversion cell can be 1.1 eV or less, the short circuit current amount of the compound semiconductor solar cell of this invention tends to become large. It is in.

  In the present invention, the first photoelectric conversion is performed by forming the n-type Ge layer after forming the n-type InGaP nucleation layer on the (100) plane of the p-type Ge substrate having an off angle of 2 ° or less. Forming a cell, and forming a second photoelectric conversion cell including a base layer including a third compound semiconductor layer and a fourth compound semiconductor layer having different band gap energies on the first photoelectric conversion cell. And forming a third photoelectric conversion cell including a base layer composed of a first compound semiconductor layer and a second compound semiconductor layer having different band gap energies on the second photoelectric conversion cell. The first compound semiconductor layer is an InGaP layer to which Sb is added, and the second compound semiconductor layer is a method for manufacturing a compound semiconductor solar cell that is an InGaP layer to which Sb is not added. By setting it as such a structure, the spectral sensitivity by the side of the long wavelength of a 3rd photoelectric conversion cell can be increased, and the short circuit current amount of the compound semiconductor solar cell of this invention can be increased.

  Furthermore, the present invention provides a base layer comprising a first compound semiconductor layer and a second compound semiconductor layer having different band gap energies on the (100) plane of a p-type GaAs substrate having an off angle of 2 ° or less. A second photoelectric conversion cell including a base layer made of a third compound semiconductor layer and a fourth compound semiconductor layer having different band gap energies on the third photoelectric conversion cell. And a step of forming the first photoelectric conversion cell on the second photoelectric conversion cell, wherein the first compound semiconductor layer is an InGaP layer to which Sb is added, In this method, the second compound semiconductor layer is an InGaP layer to which Sb is not added. By setting it as such a structure, the spectral sensitivity by the side of the long wavelength of a 3rd photoelectric conversion cell can be increased, and the short circuit current amount of the compound semiconductor solar cell of this invention can be increased.

  Moreover, the manufacturing method of the compound semiconductor solar cell of this invention further has the process of forming a compound semiconductor buffer layer between the process of forming a 2nd photoelectric conversion cell, and the process of forming a 1st photoelectric conversion cell. It is preferable to include. By setting it as such a structure, the compound semiconductor solar cell of this invention which can improve conversion efficiency is producible.

  Moreover, it is preferable that the manufacturing method of the compound semiconductor solar cell of this invention further includes the process of removing a p-type GaAs substrate. By setting it as such a structure, the compound semiconductor solar cell of this invention which can improve conversion efficiency is producible.

  The method for producing a compound semiconductor solar battery according to the present invention includes a step of forming a first tunnel junction layer between a first photoelectric conversion cell and the second photoelectric conversion cell, and a second photoelectric conversion cell. Preferably, the method further includes a step of forming a second tunnel junction layer between the first photoelectric conversion cell and the third photoelectric conversion cell. By setting it as such a structure, the compound semiconductor solar cell of this invention which can improve conversion efficiency is producible.

  As described above, the embodiments of the present invention have been described, but it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be suitably used for a compound semiconductor solar cell and a method for producing a compound semiconductor solar cell.

10 bottom cell, 20 middle cell, 30 top cell, 40a, 40b, 41a tunnel junction layer, 50 InGaP buffer layer, 51 n + type In _0.48 Ga _0.52 P layer, 52 n type In _0.51 Ga _0.49 P layer, 53 n type In _0.55 Ga _0.45 P layer, 54 n-type In _0.59 Ga _0.41 P layer, 55 n-type In _0.63 Ga _0.37 P layer, 56 n-type In _0.67 Ga _0.33 P layer, 57 n-type In _0.71 Ga _0.29 P layer, 58 n-type In _0.75 Ga _0.25 P layer, 59 n-type In _0.79 Ga _0.21 P layer, 60 n-type In _0.82 Ga _0.18 P layer, 101 p-type Ge substrate, 102 n-type Ge layer, 103 n-type InGaP nucleation layer, 104 n-type InGaAs buffer Layer, 105 n ++ type GaAs layer, 106 p ++ type GaAs layer, 107 BSF layer, 108 p type InGaAs layer, 108a p type InGaAs / GaAsP quantum well layer 108b p-type GaAs base layer doped with InAs quantum dots, 109 n-type InGaAs layer, 110 n-type InGaP window layer, 111 n ++-type InGaP layer, 112 p ++-type AlGaAs layer, 113 base layer, 114 p-type InGaP layer, 114a p-type AlGaInP layer, 114b p-type InGaP layer, p-type InGaP base layer with 114c Sb added, p-type InGaP base layer with no 114d Sb added, 115 n-type InGaP layer, 115a n-type AlGaInP 115 n-type InGaP emitter layer doped with Sb, 116 n-type AlInP window layer, 117 n-type GaAs layer, 130 GaAs substrate, 131 etching stop layer, 201 lower electrode, 202 upper electrode, 203 antireflection film, 210 Metal layer, 211 Support substrate, 300 Type InGaAs contact layer, 301 BSF layer, 302 p type InGaAs base layer, 303 n type InGaAs emitter layer, 304 n type InGaP window layer, 305 n ++ type InGaP layer, 306 p ++ type AlGaAs layer, 308 p type GaAs Base layer, 309 n-type GaAs emitter layer.

Claims (5)

A first photoelectric conversion cell;
A second photoelectric conversion cell provided on the first photoelectric conversion cell;
A third photoelectric conversion cell provided on the second photoelectric conversion cell,
The third photoelectric conversion cell includes a first compound semiconductor layer and a second compound semiconductor layer,
The band gap energy of the first compound semiconductor layer is slightly larger than the band gap energy of the second compound semiconductor layer,
A compound semiconductor solar cell, wherein an absolute value of a difference between a band gap energy of the first compound semiconductor layer and a band gap energy of the second compound semiconductor layer is 0.05 eV or less.   2. The compound semiconductor solar battery according to claim 1, wherein the first compound semiconductor layer is an AlInGaP layer and the second compound semiconductor layer is an InGaP layer.   The compound semiconductor solar cell according to claim 1, wherein the first compound semiconductor layer is an InGaP layer to which Sb is added, and the second compound semiconductor layer is an InGaP layer to which Sb is not added. Forming a first photoelectric conversion cell by forming an n-type Ge layer after forming an n-type InGaP nucleation layer on a (100) plane of a p-type Ge substrate having an off angle of 2 ° or less; Forming a second photoelectric conversion cell including a base layer composed of a third compound semiconductor layer and a fourth compound semiconductor layer having different band gap energies on the first photoelectric conversion cell; Forming a third photoelectric conversion cell including a base layer composed of a first compound semiconductor layer and a second compound semiconductor layer having different band gap energies on the photoelectric conversion cell;
A method for manufacturing a compound semiconductor solar cell, wherein the first compound semiconductor layer is an InGaP layer to which Sb is added, and the second compound semiconductor layer is an InGaP layer to which Sb is not added. Third photoelectric including a base layer composed of a first compound semiconductor layer and a second compound semiconductor layer having different band gap energies on the (100) plane of a p-type GaAs substrate provided with an off angle of 2 ° or less. A step of forming a conversion cell; and a second photoelectric conversion cell including a base layer composed of a third compound semiconductor layer and a fourth compound semiconductor layer having different band gap energies on the third photoelectric conversion cell. And forming a first photoelectric conversion cell on the second photoelectric conversion cell,
A method for manufacturing a compound semiconductor solar cell, wherein the first compound semiconductor layer is an InGaP layer to which Sb is added, and the second compound semiconductor layer is an InGaP layer to which Sb is not added.

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