KR102182902B1 - Transparent Electrodes for Solar Cells and Solar Cells Utilizing the Same Approach - Google Patents

Abstract

The present invention relates to a transparent electrode for a solar cell, wherein the transparent electrode for a solar cell according to the present invention comprises: a transparent conductive oxide layer having a first surface through which light is introduced and a second surface through which photocharge is introduced; And a buffer layer positioned in contact with the second surface; wherein the buffer layer includes a first transition metal oxide layer in contact with the second surface and a second transition metal oxide layer in contact with the first transition metal oxide layer, , The first transition metal oxide has an electron affinity smaller than that of the second transition metal oxide.

Description

Transparent Electrodes for Solar Cells and Solar Cells Utilizing the Same Approach for Solar Cells

The present invention relates to a transparent electrode for a solar cell and a solar cell including the same, and in detail, to a transparent electrode provided on the hole transport layer side of the solar cell to collect holes, and a perovskite solar cell including the same will be.

The organometallic halide of a perovskite structure, referred to as an organic-inorganic perovskite compound, consists of an organic cation (A), a metal cation (M) and a halogen anion (X), and is represented by the formula of AMX ₃ It is a substance.

Currently, perovskite solar cells using organic-inorganic perovskite compounds as light absorbers are the closest to commercialization among the next-generation solar cells including dye-sensitized and organic solar cells, and an efficiency of up to 20% is reported (Korean Patent Publication No. 2014-0035284), and interest is increasing more and more.

Such a perovskite solar cell has an efficiency comparable to that of a silicon solar cell, has a very low material cost, and is excellent in commerciality because a low-temperature process or a low-cost solution process is possible.

On the other hand, organic-inorganic perovskite compounds effectively convert blue and green light, while silicon effectively converts red and infrared light. Thus, using a tandem type solar cell in which an organic-inorganic perovskite compound-based cell and an organic-inorganic perovskite compound and other inorganic light absorber-based cells having different light absorption characteristics are combined, a solar cell Research is being conducted to further improve the power generation efficiency.

The perovskite compound-based tandem solar cell has a four-terminal tandem structure in which a translucent perovskite solar cell is mechanically stacked on top of an inorganic solar cell such as silicon, and an inorganic light absorbing layer and a perovskite compound light absorbing layer. A two-terminal tandem structure incorporating a single cell structure is known.

The dual four-terminal tandem structure does not require current (or voltage) matching and is advantageous because it can adopt the technological development made by each independent solar cell as it is, and it is also possible to tandem the conventional panels already installed such as silicon solar panels. It can be commercially advantageous.

However, in order for the light passing through the upper cell to enter the lower cell in the 4-terminal tandem structure, the upper cell, the perovskite solar cell, must be transparent (translucent) above all. Accordingly, in order to be used as an upper cell of a four-terminal tandem structure, development of a perovskite solar cell in which both counter electrodes are transparent electrodes is required. However, photoelectric conversion efficiency is reduced when both counter electrodes are transparent conductive oxide-based electrodes. There is a decreasing problem.

Republic of Korea Patent Publication No. 2014-0035284

An object of the present invention is to provide a transparent electrode for a solar cell that can have excellent photoelectric conversion efficiency when used as an electrode of a solar cell, and in detail, to provide a transparent electrode for a solar cell suitable as a transparent photoanode collecting holes. will be.

Another object of the present invention is to provide a transparent electrode for a solar cell in which damage to an organic material layer is prevented during an electrode manufacturing process, and in detail, to provide a transparent electrode for a solar cell in which damage to a hole-transporting organic material layer is prevented.

Another object of the present invention is to provide a transparent electrode for a photoanode of a translucent perovskite solar cell in which both counter electrodes are transparent electrodes.

Another object of the present invention is to provide a transparent electrode for a solar cell having a trap density corresponding to a metal electrode that is an opaque electrode.

Another object of the present invention is to provide a perovskite solar cell in which both counter electrodes are transparent electrodes and have excellent photoelectric conversion efficiency.

Another object of the present invention is to provide a translucent perovskite solar cell having a high light transmittance in a wavelength range of 800 nm or more.

Another object of the present invention is to provide a 4-terminal tandem solar cell having extremely high photoelectric conversion efficiency.

The transparent electrode for a solar cell according to the present invention includes a transparent conductive oxide layer having a first surface through which light is introduced and a second surface through which photocharge is introduced; And a buffer layer positioned in contact with the second surface; wherein the buffer layer includes a first transition metal oxide layer in contact with the second surface and a second transition metal oxide layer in contact with the first transition metal oxide layer, , The first transition metal oxide has an electron affinity smaller than that of the second transition metal oxide, and the band gap energy of the first transition metal oxide is greater than the band gap energy of the second transition metal oxide. to be.

In the transparent electrode according to an embodiment of the present invention, the work function of the first transition metal oxide may be equal to or greater than the work function of the transparent conductive oxide and may be smaller than the work function of the second transition metal oxide. have.

In the transparent electrode according to an embodiment of the present invention, the first transition metal oxide and the second transition metal oxide may each be in an oxygen-deficiency state.

In the transparent electrode according to an embodiment of the present invention, the thickness of the first transition metal oxide layer is 5 to 30 nm, and a thickness ratio obtained by dividing the thickness of the second transition metal oxide layer by the thickness of the first transition metal oxide layer is 3 to May be 20.

In the transparent electrode according to an embodiment of the present invention, the first transition metal oxide or the second transition metal oxide is niobium oxide, zirconium oxide, molybdenum oxide, hafnium oxide, tantalum oxide, tungsten oxide, or It may be a composite oxide.

The transparent electrode according to an embodiment of the present invention may be positioned in contact with the organic hole transport layer to collect light holes.

The present invention includes a solar cell provided with the above-described transparent electrode.

The present invention includes a perovskite solar cell provided with the above-described transparent electrode.

The perovskite solar cell according to the present invention comprises: a first transparent electrode; An electron transport layer positioned on the first transparent electrode; A light absorbing layer positioned on the electron transport layer and including a perovskite compound; An organic hole transport layer positioned on the light absorption layer; And a second transparent electrode, which is the above-described transparent electrode for a solar cell, positioned on the organic hole transport layer so that the organic hole transport layer and the buffer layer are in contact.

The perovskite solar cell according to an embodiment of the present invention may have a light transmittance of 75% or more at a wavelength of 850 nm.

The perovskite solar cell according to an embodiment of the present invention may be for an upper cell of a 4-terminal tandem solar cell.

The present invention includes a four-terminal tandem solar cell including the perovskite solar cell described above.

The four-terminal tandem solar cell according to the present invention includes the above-described perovskite solar cell as an upper cell, and an inorganic light absorbing layer that generates a photocurrent by absorbing light having a wavelength of 800 to 1100 nm. Is included as a lower cell.

The transparent electrode according to the present invention includes a buffer layer including a first transition metal oxide layer and a second transition metal oxide layer; And a transparent conductive oxide layer; as a result, it has resistance and interfacial properties comparable to those of a metal electrode, which is an opaque electrode, so that the fill factor of a solar cell can be remarkably improved. There is an advantage of having conversion efficiency.

In addition, since the transparent electrode according to the present invention can collect light holes very efficiently and stably, it is advantageous when used as a transparent photoanode, and both counter electrodes have the advantage of implementing a transparent transparent solar cell.

In addition, the transparent electrode according to the present invention has a very high light transmittance for a light wavelength band of 800 nm or more that the perovskite light absorber cannot absorb, and a solar cell and perovskite that generate a photocurrent by absorbing light of 800 nm or more. There is a useful advantage for tandeming between solar cells.

1 is a view showing current density-voltage measurement results of solar cells prepared in Examples 1, 2, 3, and 2;
2 is a view showing the current density-voltage measurement results of the solar cells prepared in Example 1, Comparative Example 1 and Comparative Example 2.
3 is a diagram showing measurement of light transmittance (%) of solar cells manufactured in Example 1 and Comparative Example 2. FIG.
4 is a diagram showing the results of operation stability tests of the solar cells manufactured in Example 1 and Comparative Example 2.
5 is a UV photoelectron spectroscopy of a WOx film (Fig. 5(a)), an NbOy film (Fig. 5(b)), a buffer layer of a WOx film and an NbOy film (Fig. 5(c)), and an ITO layer (Fig. 5(d)). It is a diagram showing a spectrum, FIG. 5(e) is a diagram showing a Tauc's plot of each layer, and FIG. 5(f) is a diagram showing an energy band diagram of each layer.
6 is a Niqui of a solar cell equipped with a transparent electrode (buffer layer-ITO) manufactured in Example 1, an electrode (Au) manufactured in Comparative Example 1, and a transparent electrode (WOx-ITO) manufactured in Comparative Example 2 It is a diagram showing Nyquist plots.
7(a) shows capacitance values (C≡ 1/iωZ, Z=impedance, ω=angular frequency, i=imaginary unit) of the solar cells manufactured in Example 1, Comparative Example 1, and Comparative Example 2 Fig. 7(b) is a diagram showing a trap density distribution according to an energy level Eω.
FIG. 8 is an X-ray photoelectron spectroscopy (XPS) spectrum of a WOx film (WO in FIG. 8), an NbOy film (NbOz in FIG. 8), and a buffer layer (WOy/NbOz in FIG. 8) in which a WOx film and an NbOy film are stacked. It is a drawing.
9(a) is a view showing measurement of current density-voltage graphs of each of the upper and lower cells of the tandem solar cell prepared in Example 4 and the tandem solar cell prepared in Comparative Example 3, and FIG. 9(b) Is a diagram showing the external quantum efficiency (EQE) of the upper cell (shown as a dotted line) and the lower cell (shown as a solid line) of the tandem solar cell manufactured in Example 4 and the tandem solar cell manufactured in Comparative Example 3.

Hereinafter, a transparent electrode for a solar cell and a solar cell including the same according to the present invention will be described in detail with reference to the accompanying drawings. The drawings introduced below are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, unless there are other definitions in the technical terms and scientific terms used, they have the meanings commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Description of known functions and configurations that may be unnecessarily obscure will be omitted.

The transparent electrode according to the present invention is a transparent electrode based on a transparent conductive oxide, and is an electrode for a solar cell, in particular, a transparent solar cell in which both electrodes facing each other are transparent.

The transparent electrode according to the present invention includes a transparent conductive oxide layer having a first surface through which light is introduced and a second surface through which photocharges are introduced; And a buffer layer positioned in contact with the second surface; wherein the buffer layer includes a first transition metal oxide layer in contact with the second surface and a second transition metal oxide layer in contact with the first transition metal oxide layer, , The first transition metal oxide has an electron affinity less than that of the second transition metal oxide, and the first transition metal oxide has a band gap energy greater than that of the second transition metal oxide.

In this case, the fact that the first transition metal oxide has an electron affinity smaller than that of the second transition metal oxide means that the minimum energy level Ec of the conduction band of the first transition metal oxide is the second transition metal oxide. It may mean that the conduction band of is higher than the minimum energy level Ec.

For example, the difference between the electron affinity of the first transition metal oxide and the electron affinity of the second transition metal oxide may be 0.1 eV or more, substantially 0.1 to 0.8 eV, and more substantially 0.3 to 0.5 eV, but the present invention is the first It goes without saying that the spherical electric charge evolution between the transition metal oxide and the second transition metal oxide cannot be limited by the difference.

As an example, the difference between the band gap energy of the first transition metal oxide and the band gap energy of the second transition metal oxide may be 0.05 eV or more, substantially 0.05 to 0.50 eV, and more substantially 0.05 to 0.30 eV. It goes without saying that it cannot be limited by the difference in the specific band gap energy between the first transition metal oxide and the second transition metal oxide.

Furthermore, the first transition metal oxide has a larger band gap energy than that of the second transition metal oxide, and at the same time, the maximum energy level (Ev) of the valence band of the first transition metal oxide is the second transition metal. It may be higher than the valence band maximum energy level (Ev) of the oxide.

For example, the difference between the maximum valence band energy level of the first transition metal oxide and the maximum valence band energy level of the second transition metal oxide is 0.1 eV or more, substantially 0.1 to 0.8 eV, more substantially 0.2 to 0.5 eV, and more substantially It may be 0.2 to 0.3 eV, but is not limited thereto.

In the transparent electrode according to the present invention, the first transition metal oxide film and the second transition metal oxide film satisfying the above-described energy level relationship are located under the transparent conductive oxide layer (lower based on the direction in which light is introduced). Photocurrent generated by the absorber can be very effectively and stably collected.

In detail, since the first transition metal oxide film and the second transition metal oxide film satisfying the above-described energy level relationship are located under the transparent conductive oxide layer (lower based on the direction in which light is introduced), the solar system has a remarkably low series resistance. The fill factor of the battery can be greatly improved.

In particular, when the first transition metal oxide film and the second transition metal oxide film satisfying the above-described energy level relationship are provided under the transparent conductive oxide layer, it is possible to very effectively collect photo holes among photo charges by the transparent electrode. . In this aspect, the transparent electrode of the present invention may be a photoanode for a solar cell.

As is known, the most standardized and commercially used material for a transparent electrode is a transparent conductive oxide, and the transparent conductive oxide is typically prepared using physical vapor deposition such as sputtering. In addition, when the sputtering power is lowered when the transparent conductive oxide layer is manufactured using sputtering, the electrical conductivity of the produced transparent conductive oxide is lowered, so there is a limit to lowering the sputtering power.

The transparent electrode according to the present invention effectively collects photocurrent, especially photoholes, and at the same time, even if the hole transport material of the solar cell is an organic material (organic hole transport layer), the organic hole transport layer is formed in the physical deposition process of the transparent conductive oxide layer. It can prevent damage. In this aspect, the transparent electrode of the present invention may be an electrode that is located in contact with the organic hole transport layer and collects light holes. That is, the transparent electrode of the present invention may be a photoanode for a solar cell positioned above the organic hole transport layer in contact with the organic hole transport layer of the solar cell.

Advantageously, the work function of the first transition metal oxide may be equal to or greater than the work function of the transparent conductive oxide and may be smaller than the work function of the second transition metal oxide. In a specific example, the work function of the first transition metal oxide may be equal to or greater than the work function of the transparent conductive oxide from 0.01 to 0.20 eV, and may be substantially greater than from 0.02 to 0.10 eV, and from 0.10 to 0.70 eV than the work function of the second transition metal oxide. , It may be substantially smaller than 0.30 to 0.60 eV, but the present invention cannot be limited by the difference in the specific work function between the first transition metal oxide, the second transition metal oxide, and the transparent conductive oxide.

When the first transition metal oxide has the above-described work function relationship with the transparent conductive oxide and the second transition metal oxide, the transparent conductive oxide layer-the first transition metal oxide film-the second transition metal oxide film in the balanced transparent electrode Energy level matching is performed, so that the photo current can more smoothly flow from the second transition metal oxide layer to the transparent conductive oxide layer. In addition, when the transparent electrode satisfies the above-described energy level and work function relationship, it has a resistance characteristic substantially similar to that of a metal electrode that is an opaque electrode, and thus photoelectric conversion efficiency of a solar cell can be greatly improved.

In one embodiment, the thickness of the first transition metal oxide layer may be 5 to 30 nm, preferably 10 to 25 nm, and more preferably 15 to 25 nm, and the thickness of the second transition metal oxide layer may be defined as the thickness of the first transition metal oxide layer. The thickness ratio divided by may be 3 to 20, preferably 3 to 10, and more preferably 3 to 5. The ratio of the thickness of the first transition metal oxide layer to the thickness between the second transition metal oxide layer and the first transition metal oxide layer is suitable for transparent solar cells or tandem solar cells because the transparent electrode can exhibit a light transmittance of 80% or more over the entire wavelength range of 500 to 1200 nm. It can be used effectively.

More advantageously, the refractive index of the first transition metal oxide may be greater than the refractive index of the transparent conductive oxide and the second transition metal oxide. The layered structure of a relatively low refractive index transparent conductive oxide layer- a relatively high refractive index first transition metal oxide film- a relatively low refractive index second transition metal oxide film laminate structure itself reflects light, especially in the 800 to 900 nm wavelength band. It is advantageous to reduce In this case, the refractive index of the second transition metal oxide may be equal to or greater than the refractive index of the transparent conductive oxide.

For example, the refractive index (relative refractive index) of the first transition metal oxide may be 0.1 or more greater than the refractive index of each of the transparent conductive oxide and the second transition metal oxide, specifically 0.2 to 1.0, and more specifically 0.2 to 0.5, It is not limited thereto.

The energy level and work function of the first and second transition metal oxides described above are in the oxidation state in which the transition metal oxide (the first transition metal oxide or the second transition metal oxide) satisfies the stoichiometric ratio or the oxygen deficiency. It may be the energy level and work function in the oxidation state.

At this time, the work function, band gap energy, and minimum valence band energy level of the transition metal oxide in the oxygen-deficient state are measured using the photoelectron spectral spectrum of the transition metal oxide as known and calculated using Tauc's plot. can do.

In one embodiment, the first transition metal oxide and the second transition metal oxide may each be in an oxygen-deficiency state. Since the buffer layer includes transition metal oxide films (first transition metal oxide film and second transition metal oxide film) in an oxygen-deficient state, when a transparent electrode according to an embodiment of the present invention is provided in a solar cell, a deep trap is It can effectively suppress the formation.

Each of the first transition metal oxide and the second transition metal oxide may be in a state of lack of oxygen based on a stoichiometric ratio. The first transition metal oxide is 0.8 to 0.98 standard moles (0.8M ₁ ) when the number of moles of oxygen required according to the stoichiometric ratio of the oxide to 1 mole of the first transition metal contained in the oxide is the standard mole number (M ₁ ). It may be in a state of lack of oxygen containing oxygen of ~0.98M ₁ ). In addition, for the second transition metal oxide, when the number of moles of oxygen required according to the stoichiometric ratio of the oxide to 1 mole of the second transition metal contained in the oxide is the reference mole number (M ₂ ), 0.7 to 0.97 reference mole number (0.7 M ₂ ~ 0.97M ₂ ) It may be a state of lack of oxygen containing oxygen. At this time, when two or more kinds of nitrides with different stoichiometric ratios naturally exist, the oxide that is the basis of the stoichiometric ratio in the first transition metal oxide or the second transition metal oxide is the most thermodynamically stable oxide at room temperature and pressure ( Of course, it may be an oxide with the lowest Gibbs free energy). As an example, as a transition metal oxide according to a stoichiometric ratio, WO ₃ , Nb ₂ O _5, etc. may be mentioned.

In one embodiment, the first transition metal oxide and the second transition metal oxide may be intermixed at an interface between the first transition metal oxide layer and the second transition metal oxide layer of the buffer layer. Since the above-described buffer layer has a thickness ratio between the thickness of the first transition metal oxide layer and the thickness of the first transition metal oxide layer and the second transition metal oxide layer, and has a structure intermixed at the interface, the overall electrical characteristics of the buffer layer are mainly first. It may be controlled by the transition metal oxide film, and overall electrical characteristics of the buffer layer may be similar to that of the first transition metal oxide film.

The first transition metal oxide and the second transition metal oxide may be any material as long as they are oxides of transition metals that satisfy the above-described energy level relationship, and advantageously, the above-described energy level relationship and refractive index relationship. As a non-limiting example, the first transition metal oxide and the second transition metal oxide are each selected from niobium oxide, zirconium oxide, molybdenum oxide, hafnium oxide, tantalum oxide, tungsten oxide, or a composite oxide thereof. Any material that satisfies one energy level relationship, advantageously the energy level relationship and the refractive index relationship described above, may be used.

Transparent conductive oxides are ITO (Indium Tin Oxide) in which tin (Sn) is substituted for indium oxide (In ₂ O ₃ ), ATO (Antimony Tin Oxide) in which Sb is substituted for tin oxide (SnO ₂ ), and zinc oxide ( ZnO) is a conductive oxide used as a transparent conductive film, such as AZO (Aluminium-doped Zinc Oxide) or GZO (Gallium-doped Zinc Oxide). In this case, the thickness of the transparent conductive oxide layer may be a thickness that can ensure stable electrical conductivity, and may be, for example, 100 to 300 nm, but is not limited thereto.

In one embodiment, the transparent conductive oxide layer, the first transition metal oxide layer, and the second transition metal oxide layer may be formed by evaporation, respectively, and each layer may be formed by physical vapor deposition such as sputtering, electron beam evaporation, and thermal evaporation. Although it may be manufactured, it goes without saying that the present invention cannot be limited by the specific deposition method of each film (layer) included in the transparent electrode.

The present invention includes a solar cell including the above-described transparent electrode.

In a specific embodiment, the present invention includes a solar cell including the above-described transparent electrode as a photoanode. At this time, the solar cell is a perovskite solar cell in which the light absorber is an organic/inorganic perovskite compound, a dye-sensitized solar cell in which the light absorber is a dye, a quantum dot-sensitized solar cell in which the light absorber is an inorganic quantum dot, and the light absorber is Organic solar cell as an organic semiconductor, compound semiconductor solar cell in which the light absorber is a compound semiconductor such as CIS (Cu-In-(S, Se)), CIGS (Cu-In-Ga-(S, Se)), GaAs, CdTe, etc. , Silicon solar cell, and the cell structure and material of a solar cell other than the photoanode that collects light holes among the photo charges generated from the light absorber may have a structure and material previously known in each spherical solar cell. to be.

The transparent electrode according to the present invention can prevent damage to the organic hole transport layer during manufacturing of the transparent electrode even when the organic hole transport layer is located in contact with the transparent electrode. Accordingly, the transparent electrode according to the present invention is a perovskite It can be effectively used as a photoanode of solar cells or organic solar cells.

According to an advantageous example, the present invention includes a perovskite solar cell including the above-described transparent electrode. At this time, the perovskite solar cell may mean a solar cell containing a perovskite compound as a light absorber. The perovskite compound refers to an organometallic halide having a perovskite structure and satisfies the formula of AMX ₃ based on organic cation (A), metal cation (M) and anion (X), and at the same time, A (organic Cation) is AX ₁₂ , which combines with 12 X (anions) to form a cubic octahedral structure, and M (metal cation) is MX ₆ , meaning an organometallic halide having a three-dimensional structure combined with X (anion) and octahedral structure. can do.

Specifically, the perovskite solar cell according to the present invention includes a first electrode; An electron transport layer positioned on the first electrode; A light absorbing layer positioned on the electron transport layer and including a perovskite compound; An organic hole transport layer positioned on the light absorption layer; And a second transparent electrode, which is the above-described transparent electrode, positioned on the organic hole transport layer so that the organic hole transport layer and the buffer layer are in contact with each other. In this case, the first electrode may be a transparent electrode or an opaque electrode (metal electrode). When the first electrode is a transparent electrode, the perovskite solar cell may be a transparent (translucent when light absorption by a perovskite compound is considered) in which both electrodes facing each other are transparent electrodes.

The first electrode is not particularly limited as long as it is commonly used in the art, and when the first electrode is a transparent electrode, the first electrode may be a transparent conductive electrode that is ohmic-bonded with the electron transport layer. As a specific example, the first electrode, which is a transparent electrode, includes fluorine doped tin oxide (FTO), indium doped tin oxide (ITO), ZnO, carbon nanotube, graphene ( graphene) and composites thereof. When the first electrode is an opaque electrode, the first electrode may include any one or two or more materials selected from gold, silver, platinum, palladium, copper, aluminum, carbon, cobalt sulfide, copper sulfide, nickel oxide, and composites thereof. However, it is not limited thereto.

At this time, the first electrode is a deposition process such as physical vapor deposition or chemical vapor deposition on a transparent substrate (support) that is a rigid substrate (support) or a flexible substrate (support). It may be formed through, and specifically, may be formed by thermal evaporation. As an example of a transparent substrate (support), the rigid substrate may be a glass substrate, and the flexible substrate is polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polycarbonate (PC), polypropylene ( PP), triacetyl cellulose (TAC) or polyethersulfone (PES), etc., but the present invention is not limited to the specific material of the substrate.

The electron transport layer may be an inorganic material and may include a metal oxide. The electron transport layer is a flat metal oxide layer, a metal oxide layer having surface irregularities, and a nanostructure of the same or different metal oxides on the surface of one metal oxide in the form of a thin film (including metal oxide particles, nanowires and/or nanotubes) It may be a metal oxide layer, a dense metal oxide layer, or a porous metal oxide layer having a composite structure in which is formed. As a practical example, the electron transport layer may be a laminated film of a dense film and a porous film, more specifically, a laminate film of a metal oxide film (dense film) and a meso-porous metal oxide film.

The metal oxide film (dense film) may be formed through a vapor deposition process such as physical vapor deposition or chemical vapor deposition, or through coating and heat treatment of metal oxide nanoparticles.

The porous metal oxide film may include metal oxide particles, and may have a porous structure opened by an empty space between the particles.

In one example, the porous metal oxide film may be prepared by applying a slurry containing metal oxide particles on the metal oxide film (dense film), and drying and heat treatment of the applied slurry layer. The slurry is applied in screen printing, spin coating, bar coating, gravure coating, blade coating and roll coating. It may be carried out in any one or two or more methods selected.

The main factors affecting the specific surface area and open pore structure of the porous metal oxide film are the average particle size of the metal oxide particles and the heat treatment temperature. The average particle size of the metal oxide particles may be 5 to 500 nm, and the heat treatment may be performed at 200 to 600° C. in air, but is not limited thereto.

The thickness of the electron transport layer may be, for example, 50 nm to 10 μm, specifically 50 nm to 5 μm, more specifically 50 nm to 1 μm, and even more specifically 50 to 800 nm. It is not limited.

The metal oxide of the electron transport layer may be used without particular limitation as long as it is a metal oxide commonly used for the movement of photoelectrons in the field of solar cells, particularly perovskite solar cells. Specifically, for example, Ti oxide, Zn oxide, In oxide, Sn oxide, W oxide, Nb oxide, Mo oxide, Mg oxide, Zr oxide, Sr oxide, Yr oxide, La oxide, V oxide, Al oxide, Y oxide, It may be any one or two or more selected from Sc oxide, Sm oxide, Ga oxide, In oxide, and SrTi oxide and composites thereof.

The thickness of the light-absorbing layer is not particularly limited, but may be 100 nm to 1 μm, as a specific example, 200 to 800 nm.

The perovskite compound of the light absorption layer may satisfy the following Chemical Formulas 1, 2, or 3.

(Chemical Formula 1)

AMX ₃

In Formula 1, A is a monovalent organic ammonium ion or Cs ⁺ , M is a divalent metal ion, and X is a halogen ion.

(Chemical Formula 2)

A ₂ MX ₄

In Formula 2, A is a monovalent organic ammonium ion or Cs ⁺ , M is a divalent metal ion, and X is a halogen ion.

(Chemical Formula 3)

B _1-x A _x MX ₃

In Formula 3, A is a monovalent organic ammonium ion, B is a monovalent amidium ion, M is a divalent metal ion, X is a halogen ion, x is 0<x<1, advantageously 0.01≤ x≤0.1, more advantageously, a real number of 0.02≤x≤0.06.

In Formula 1, 2 or 3, the organic ammonium ion may be R ₁ -NH ₃ ⁺ (R ₁ is C1-C24 alkyl, C3-C20 cycloalkyl or C6-C20 aryl), and in Formula 3 Niium-based ions may satisfy the following Chemical Formula 4.

(Formula 4)

In Formula 4, R ₂ to R ₆ are each independently hydrogen, C1-C24 alkyl, C3-C20 cycloalkyl, or C6-C20 aryl. In Formula 4, R ₂ to R ₆ may be appropriately selected depending on the use of the perovskite compound. In detail, the size of the unit cell of the perovskite compound is related to the band gap, and the small unit cell size may have a band gap energy suitable for use as a solar cell (eg, 1.1 to 1.5V level). Accordingly, when considering a band gap energy suitable for use as a solar cell, R ₂ to R ₆ are independently of each other, hydrogen, amino or C1-C24 alkyl, specifically, hydrogen, amino or C1-C7 alkyl, More specifically, it may be hydrogen, amino or methyl, and even more specifically, R ₂ may be hydrogen, amino or methyl, and R ₃ to R ₆ may be hydrogen. As a practical example, the amidinium-based ion is a formamidinium (formamidinium, NH ₂ CH=NH ₂ ⁺ ) ion, acetamidinium (acetamidinium, NH ₂ C(CH ₃ )=NH ₂ ⁺ ) ion or guamidi Nium (Guamidinium, NH ₂ C (NH ₂ ) = NH ₂ ⁺ ) ions and the like, but are not limited thereto. Such an example is an example considering the use of a perovskite compound, that is, as a light absorber of sunlight, design of the wavelength band of light to be absorbed, design of the emission wavelength band when used as a light emitting layer of a light emitting device, When used as a semiconductor device of a transistor, R ₂ to R ₆ may be appropriately selected in consideration of an energy band gap and a threshold voltage.

In Formula 1, 2 or 3, M is Cu ²⁺ , Ni ²⁺ , Co ²⁺ , Fe ²⁺ , Mn ²⁺ , Cr ²⁺ , Pd ²⁺ , Cd ²⁺ , Ge ²⁺ , Sn ²⁺ , It may be one or two or more metal ions selected from Pb ²⁺ and Yb ²⁺ .

Formula 1, 2 or 3, X is Cl ^-, Br ^- and I ^- in one or may be two or halogen ion selected above, as well as one days halogen ion, two or more halogen ion, that is, the formula 1, 2 or 3 X=X ^a _x X ^b _y (real number 0<x<1, real number 0<y<1, x+y=1, and X ^a and X ^b are different halogen ions). In one embodiment, X may include I and Br, and in Formula 1, 2 or 3, X is (I _1-x Br _x ) (0<x<1, a real number, preferably 0.01≦x≦0.15 , More preferably 0.01≦x≦0.10).

The light absorbing layer may be prepared by using a conventional solution coating method in which a light absorber solution in which the above-described perovskite compound is dissolved in a solvent is applied and dried. A method of removing solvent molecules from the adduct film after forming the adduct film of the solvent-perovskite compound using a solvent that forms an adduct with a perovskite compound such as dimethyl sulfoxide, light absorber solution and perovskite It may be prepared using a method disclosed by the present applicant, such as a method of sequentially applying a non-solvent of the skyt compound.

The hole transport layer may be an organic hole transport layer, and the organic hole transport material of the organic hole transport layer may be a single molecule or a polymer organic hole transport material. One non-limiting example of a single- or low-molecular organic hole transport material, such as pentacene, coumarin 6, 3-(2-benzothiazolyl)-7-(diethylamino)coumarin), zinc phthalocyanine (ZnPC), CuPC (copper phthalocyanine), TiOPC (titanium oxide phthalocyanine), Spiro-MeOTAD(2,2',7,7'-tetrakis(N,Np-dimethoxyphenylamino)-9,9'-spirobifluorene), F16CuPC(copper(II) 1 ,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluoro-29H,31H-phthalocyanine), Boron subphthalocyanine chloride (SubPc) and N3 (cis -di(thiocyanato)-bis(2,2'-bipyridyl-4,4'-dicarboxylic acid)-ruthenium(II)) may be mentioned, but the material is not limited thereto.

A non-limiting example of a high molecular organic hole transport material, P3HT (poly[3-hexylthiophene]), MDMO-PPV (poly[2-methoxy-5-(3',7'-dimethyloctyloxyl)]-1,4-phenylene vinylene), MEH-PPV(poly[2-methoxy -5-(2''-ethylhexyloxy)-p-phenylene vinylene]), P3OT(poly(3-octyl thiophene)), POT(poly(octyl thiophene)), P3DT(poly(3-decyl thiophene)), P3DDT(poly(3-dodecyl thiophene), PPV(poly(p-phenylene vinylene)), TFB(poly(9,9'-dioctylfluorene-co-N-(4- butylphenyl)diphenyl amine), Polyaniline, Spiro-MeOTAD ([2,22′,7,77′-tetrkis (N,N-di-p-methoxyphenyl amine)-9,9,9′-spirobi fluorine]), PCPDTBT (Poly[2,1,3-benzothiadiazole- 4,7-diyl[4,4-bis(2-ethylhexyl-4H- cyclopenta [2,1-b:3,4-b']dithiophene-2,6- diyl]], Si-PCPDTBT(poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-( 2,1,3-benzothiadiazole)-4,7-diyl]), PBDTTPD(poly((4,8-diethylhexyloxyl) benzo([1,2-b:4,5-b']dithiophene)-2,6 -diyl)-alt-((5-octylthieno[3,4-c]pyrrole-4,6-dione)-1,3-diyl)), PFDTBT(poly[2,7-(9-(2-ethylhexyl) )-9-hexyl-fluorene)-alt-5,5-(4', 7, -di-2-thienyl-2',1' , 3'-benzothiadiazole)]), PFO-DBT(poly[2,7-.9,9-(dioctyl-fluorene)-alt-5,5-(4',7'-di-2-.thienyl- 2', 1', 3'-benzothiadiazole)]), PSiFDTBT(poly[(2,7-dioctylsilafluorene)-2,7-diyl-alt-(4,7-bis(2-thienyl)-2,1, 3-benzothiadiazole)-5,5′-diyl]), PSBTBT(poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2 ,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl]), PCDTBT(Poly [[9-(1-octylnonyl)-9H-carbazole-2,7-diyl] -2 ,5-thiophenediyl -2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]), PFB (poly(9,9′-dioctylfluorene-co-bis(N,N′-(4, butylphenyl))bis(N,N′-phenyl-1,4-phenylene)diamine), F8BT(poly(9,9′-dioctylfluorene-co-benzothiadiazole), PEDOT (poly(3,4-ethylenedioxythiophene))), PEDOT :PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)), PTAA (poly(triarylamine)), poly(4-butylphenyl-diphenyl-amine), and one or more selected materials from their copolymers. However, it is not limited thereto.

The hole transport layer is TBP (tertiary butyl pyridine), LiTFSI (Lithium Bis (Trifluoro methanesulfonyl) Imide), HTFSI (bis (trifluoromethane) sulfonimide), 2,6-lutidine and Tris(2-(1H-pyrazol-1-yl) Of course, it may further contain known additives such as pyridine) cobalt (III).

The thickness of the hole transport layer may be 10 to 500 nm, but is not limited thereto.

The hole transport layer may be performed by applying and drying a solution containing an organic hole transport material (hereinafter, an organic hole transport solution) on the light absorption layer. The solvent used to form the hole transport layer may be a solvent in which an organic hole transport material is dissolved and does not chemically react with the perovskite compound and the material of the electron transport layer. As an example, the solvent used to form the hole transport layer may be a non-polar solvent, and as a practical example, toluene, chloroform, chlorobenzene, dichlorobenzene, anisole ( anisole), xylene, and a hydrocarbon-based solvent having 6 to 14 carbon atoms, but is not limited thereto.

The above-described transparent electrode may be positioned on the organic hole transport layer in contact with the organic hole transport layer, and specifically, a second transition metal oxide film and a second transition metal oxide positioned on the organic hole transport layer in contact with the organic hole transport layer. A buffer layer including a first transition metal oxide film positioned on the film; And a transparent conductive oxide layer positioned on the first transition metal oxide layer of the buffer layer.

For the transparent electrode, a second transition metal oxide layer and a first transition metal oxide layer are sequentially formed on the organic hole transport layer using a vapor deposition method such as thermal evaporation, and then a transparent conductive oxide layer is formed using a deposition method such as RF sputtering. It can be produced by forming a layer.

The present invention includes a four-terminal tandem solar cell including the above-described perovskite solar cell in which the first electrode is a transparent electrode as an upper cell.

Specifically, in the four-terminal tandem solar cell according to the present invention, the above-described perovskite solar cell in which the first electrode is a transparent electrode is used as an upper cell, and an inorganic light absorbing layer that generates a photocurrent by absorbing light of 800 nm or more. It includes the provided inorganic solar cell as a lower cell (cell).

Due to the four-terminal tandem structure, a solar cell provided as a lower cell may be any conventional solar cell capable of producing photovoltaic power by itself as long as it absorbs light of 800 nm or more to generate a photocurrent.

For example, a solar cell provided as a lower cell may be a silicon solar cell, and a silicon solar cell based on a crystalline phase may include a single crystal, polycrystalline or amorphous Si solar cell, and the silicon solar cell in structure is TOPCon (Tunnel Oxide Passivated Contact ) Structure, n-PERT (Passivated Emitter Rear Total Diffused) structure, HBC (Heterojuction Back Contact) structure or structure, PERC (Passivated Emitter and Rear Contact) structure, etc. may include a silicon solar cell. However, the inorganic light absorber is not limited to silicon, and it goes without saying that the lower cell may be a compound semiconductor solar cell such as CIGS or GaAs as the lower cell.

(Example 1)

A 20mM concentration of titanium diisopropoxide bis (acetylacetonate) solution on an FTO substrate (a glass substrate coated with fluorine-containing tin oxide, FTO; F-doped SnO ₂ , 8 ohms/cm ² , Pilkington) at 450°C Spray pyrolysis to prepare a 60nm TiO ₂ thin film.

Thereafter, an anatase-shaped TiO ₂ nanoparticle paste (SC-HT040, ShareChem, Korea) with an average diameter of 50 nm was spin-coated on a TiO2 thin film and calcined at 500°C in air for 1 hour to form a 100 nm-thick porous TiO ₂ layer. I did.

Thereafter, the perovskite solution was spin-coated on the porous TiO ₂ layer at 1000 rpm for 5 seconds and 5000 rpm for 20 seconds, but 1 ml of diethyl ether was injected after 12 seconds from the start of coating during the spin coating of the perovskite solution, and spin After the coating was completed, annealing was performed at 150° C. for 10 minutes to form a light-absorbing layer, a perovskite compound layer having a composition of (FAPbI ₃ ) _1-z (MAPbBr ₃ )z (FA=formamidinium, MA=methylammonium, z=0.05). . At this time, the perovskite solution was 889 mg/ml FAPbI ₃ (FA=formamidinium), 33 mg/ml MAPbBr ₃ (MA=methylammonium), and 33 mg/ml MACl (MA=methylammonium) in dimethylformamide (DMF ) And dimethyl sulfoxide (DMSO) mixed solvent (DMF:DMSO = 8:1 v/v) FAPbI ₃ , It was prepared by adding and dissolving MAPbBr ₃ , and MACl.

Thereafter, an organic hole transport solution was spin-coated on the prepared light absorption layer at 3000 rpm for 30 seconds to form an organic hole transport layer. At this time, the organic hole transport solution was added to 11 mg/ml of PTAA (poly(triarylamine)) in toluene, and 3.7 μl of Li-TFSI (Li-bis(trifluoromethanesulfonyl)imide) acetonitrile solution (340 mg/ml) and It was prepared by mixing 3.7µl of t BP (4-tert-butylpyridine).

Thereafter, a tungsten oxide film having a thickness of 85 nm on the organic hole transport layer prepared using a thermal evaporator was thermally evaporated (substrate temperature 50°C), and then aged to a thickness of 20 nm on the tungsten oxide film using the same thermal evaporator. An obium oxide film was thermally evaporated (substrate temperature of 80°C) to prepare a buffer layer.

Thereafter, ITO (Indium Tin Oxide) was deposited to a thickness of 150 nm on the niobium oxide film of the buffer layer by using room temperature DC magnetron sputtering to form a transparent conductive oxide layer. The sheet resistance of the prepared ITO layer was 15 ohm/sq.

Thereafter, an Au finger bar having a thickness of 70 nm was formed on the ITO layer using a thermal evaporator and a shadow mask.

In the case of forming an anti-reflection (AR) coating layer, a commercial anti-reflective film (NuShield) is attached to the glass/FTO substrate side of the manufactured solar cell, and LiF is thermally evaporated to a thickness of 175 nm on the ITO layer with Au finger bars. I did.

(Example 2)

A solar cell was manufactured in the same manner as in Example 1, except that a niobium oxide film was formed with a thickness of 5 nm instead of 20 nm on the tungsten oxide film in Example 1.

(Example 3)

A solar cell was manufactured in the same manner as in Example 1, except that the niobium oxide film was formed with a thickness of 30 nm instead of 20 nm on the tungsten oxide film in Example 1.

(Example 4)

The perovskite solar cell prepared in Example 1 was used as the upper cell, and the PERC type (passivated emitter and rear cell type) Si solar cell was used as the lower cell, and the upper cell was simply stacked on the lower cell to form a 4-terminal tandem solar cell. Was prepared.

To manufacture a PERC type Si solar cell, a 1cmx1cm p-type Si single crystal wafer (resistance 1 Ω·cm) was heat-treated at 1050°C in a mixed gas atmosphere of trichloroethane and oxygen to place silicon on the upper surface of the p-type Si single crystal wafer. An oxide film was formed and heat-treated at 830° C. for 20 minutes using a solid P source to dop (heat diffusion) P to the Si single crystal wafer, and diffuse B to the lower side of the rear Al electrode (contact).

(Comparative Example 1)

Perform the same as in Example 1, but after forming the organic hole transport layer, without depositing the tungsten oxide film, niobium oxide film, and ITO, directly on the organic hole transport layer using a thermal evaporator Au electrode (70 nm thick ) To prepare a reference solar cell.

In the case of forming an anti-reflection (AR) coating layer, a commercial non-reflective film (NuShield) was attached only to the glass/FTO substrate side of the manufactured solar cell, as an opaque solar cell was manufactured by an Au electrode.

(Comparative Example 2)

In the same manner as in Example 1, except that the niobium oxide film was not deposited after the tungsten oxide film was deposited, ITO was deposited directly on the tungsten oxide and Au finger bars were formed to manufacture a solar cell.

In the case of forming an anti-reflection (AR) coating layer, a commercial anti-reflective film (NuShield) is attached to the glass/FTO substrate side of the manufactured solar cell, and LiF is thermally evaporated to a thickness of 175 nm on the ITO layer with Au finger bars. I did.

(Comparative Example 3)

In the same manner as in Example 4, a tandem solar cell was manufactured using the solar cell prepared in Comparative Example 2 instead of the solar cell prepared in Example 1 as an upper cell.

The manufactured solar cell is characterized by using a Keithley 2420 source meter and a solar simulator (Newport Oriel Class A 91195A) using a 450W Xe-lamp Oriel with an AM 1.5G filter, using a standard 100mW/cm ² (1 SUN). ) Was measured under conditions. Current density versus voltage (JV) was measured in the range of 1.5V to -0.2V in steps of 10mV and scan speed of 150mV/sec. When measuring the characteristics of the solar cell manufactured in Example, the active area was 0.0707cm ² , and when measuring the characteristics of the solar cell manufactured in Comparative Example, the active area was 0.094cm ² .

The solar cell operation stability test was performed by maximum power point tracking (MPPT) under the condition of 100mW/cm ² (1 SUN). During characterization and testing, ambient temperature and humidity were performed at 25° C. and 30% relative humidity.

External quantum efficiency (EQE) measurement was performed using a quantum efficiency measuring device (Newport, Model Quantx-300) at room temperature (25°C) in air. Impedance spectroscopy was performed using an electrochemical impedance spectroscopy (EIS) system (model PGSTAT302N, AUTOLAB), and was performed by sweep from 1 MHz to 10 mHz. During impedance spectroscopy, the open circuit voltage (V _OC ) was swept from 1 MHz to 10 mHz under AM 1.5 G.

Regarding the analysis of the transparent conductive oxide layer and the buffer layer, light transmittance and absorption spectrum were obtained using a UV-visible spectrophotometer (Shimadzu UV 2550) for a wavelength of 300 to 1200 nm. The work function and valence band maximum energy level of each material layer was determined by ultraviolet photoelectron spectroscopy (UPS) with photon energy of 21.22 eV. The oxidation state of each material was analyzed using X-ray photoelectron spectroscopy (XPS, Thermo Scientific, Al Kα source).

The JV characteristics of the 4-terminal tandem solar cell were measured under 100mW/cm ² conditions using an AAA solar simulator (Abet Technologies, Inc) and a source meter (Keithley 2400), and a scan of 0.1V/sec at room temperature (25℃) Measured by speed. The external quantum efficiency (EQE) of the 4-terminal tandem solar cell was measured using the PV Measurement QXE7 Spectral Response system using monochromatic light from a xenon arc lamp. The EQE was calibrated using a certified reference cell for two wavelength ranges of 300-100nm and 1000-1400nm. In tandem solar cells, JV and EQE measurements were made for each of a silicon solar cell (lower cell) and a perovskite solar cell (upper cell).

Hereinafter, in the drawings and tables presented,'WOx/NbOy' means the result of the solar cell manufactured in Example 1, unless specifically described in the Example, and the result of the solar cell manufactured in Example 1 without an anti-reflective coating layer. Means. 'WOx/NbOy-AR' also refers to the result of the solar cell manufactured in Example 1, unless specifically described in Example, and refers to the result of the solar cell manufactured in Example 1 provided with an anti-reflective coating layer. 'Au' means the result of the solar cell manufactured in Comparative Example 1 without an anti-reflective coating layer,'Au-AR' means the result of the solar cell manufactured in Comparative Example 1 equipped with an anti-reflective coating layer, ' WOx' refers to the result of the solar cell prepared in Comparative Example 2 without an anti-reflective coating layer, and'WOx-AR' refers to the result of the solar cell prepared in Comparative Example 2 with an anti-reflective coating layer. In addition, in the drawings and tables presented below, when AR is not described, it means a result measured using a solar cell in which an anti-reflective film is not formed.

1 is a view showing current density-voltage measurement results of solar cells prepared in Examples 1, 2, 3, and 2; In FIG. 1, 0nm, 5nm, 20nm and 30nm refer to the thickness of the niobium oxide film, 0nm refers to the result of the solar cell prepared in Comparative Example 2, 20nm refers to the result of the solar cell prepared in Example 1, 5nm Is the result of the solar cell manufactured in Example 2, and 30 nm is the result of the solar cell manufactured in Example 3.

Table 1 shows the short-circuit current density (J _SC ), open circuit voltage (V _OC ), fill factor (FF), and photoelectric conversion efficiency of the solar cells prepared in Example 1, Example 2, Example 3, and Comparative Example 2. η), parallel resistance (R _SH ) and series resistance (R _S ) are summarized.

(Table 1)

As can be seen from Fig. 1 and Table 1, it can be seen that the solar cell manufactured in Example has a very improved fill factor compared to the solar cell of Comparative Example 2 provided with a single tungsten oxide film, and the solar cell of Comparative Example 2 and It can be seen that it has similar or better shunt characteristics and has a series resistance reduced to a level of 40% compared to the solar cell of Comparative Example 2.

It can be seen that the photoelectric conversion efficiency of the solar cell equipped with the transparent electrode according to the present invention is improved to reach 121% compared to the photoelectric conversion efficiency of the solar cell of Comparative Example 2 due to the improved resistance characteristics and fill factor.

2 is a view showing the current density-voltage measurement results of the solar cells prepared in Example 1, Comparative Example 1 and Comparative Example 2, Table 2 is a solar cell prepared in Example 1, Comparative Example 1 and Comparative Example 2 The short circuit current density (J _SC ), open circuit voltage (V _OC ), fill factor (FF), photoelectric conversion efficiency (η), parallel resistance (R _SH ), and series resistance (R _S ) of the battery are summarized.

(Table 2)

As can be seen from Figure 2 and Table 2, in the case of a solar cell equipped with a transparent electrode manufactured according to an embodiment of the present invention, the open circuit voltage and saturation current close to the reference solar cell provided with the opaque metal electrode Au It can be seen that it has a density, and furthermore, it can be seen that it has a better fill factor than the standard solar cell. In addition, although the resistance characteristic is slightly inferior to the reference battery, it can be seen from FIG. 1 and Table 1 that it has remarkably superior resistance characteristics than Comparative Example 2 in which a single transition metal oxide film is provided as salpin. In addition, it can be seen that when the saturation current density is increased by forming an antireflection coating layer, photoelectric conversion efficiency can be improved from 19.5% to 19.7%.

3 is a diagram illustrating measurement of light transmittance (%) of the solar cell manufactured in Comparative Example 2 and the solar cell manufactured in Example 1. FIG. In the case of the transparent electrode according to the exemplary embodiment of the present invention, as the transition metal oxide layer, which is a double layer, is positioned under the transparent conductive oxide layer, it can be expected that the light transmittance will be lower than that of Comparative Example 2 in which a single transition metal oxide layer is provided. . However, as can be seen from FIG. 3, it can be seen that the light transmittance of the solar cell prepared in Example 1 is not significantly different from the light transmittance of the solar cell prepared in Comparative Example 2. Further, it can be seen that in the 800 ~ 900nm wavelength band, it has a higher light transmittance (75% or more) than Comparative Example 2. This is due to the transparent electrode structure of the transparent conductive oxide-the first transition metal oxide film having a greater refractive index than the transparent conductive oxide and the second transition metal oxide-the second transition metal oxide film, so that the wavelength band is effectively absorbed by an inorganic light absorber such as Si. This is a result showing that the light transmittance is further improved. Through additional experiments, when the anti-reflective coating layer was formed, the name was confirmed at an average transmittance of 71.5% in the 800-1100 nm band.

4 is a diagram showing the results of operation stability tests of the solar cells manufactured in Example 1 and Comparative Example 2. As can be seen from FIG. 4, it can be seen that the photoelectric conversion efficiency of the solar cell manufactured in Example 1 is not decreased and substantially maintained as it is, even when 1 SUN of light is continuously irradiated. On the other hand, in the case of the solar cell manufactured in Comparative Example 2, it can be seen that the light irradiation time increases and the photoelectric conversion efficiency continues to decrease, and at the time of irradiation of 60 minutes, the efficiency decreases to 85% of the initial photoelectric conversion efficiency. It can be seen that it occurs.

2 to 4, a solar cell equipped with a transparent electrode according to an embodiment of the present invention has translucency having excellent light transmittance for a wavelength band of 800 nm or more, while a conventional opaque solar cell (for example, Example It can be seen that it exhibits excellent photoelectric conversion efficiency comparable to that of the solar cell manufactured in step 1) and has very excellent operation stability.

5 is a WOx film (Fig. 5(a)), an NbOy film (Fig. 5(b)), a buffer layer of a WOx film and an NbOy film (Fig. 5(c)) prepared by the same method and thickness as the method presented in Example 1 , It is a diagram showing the ultraviolet photoelectron spectral spectrum of the ITO layer (FIG. 5(d)), FIG. 5(e) is a diagram showing the Tauc's plot of each film, and FIG. 5(f) is the energy of each film. It is a diagram showing a band diagram. In FIG. 5(e), α is an absorption coefficient, and the band gap energy of each film can be calculated through a tau plot. The energy band diagram of FIG. 5(f) is an energy band diagram in which the WOx film, the NbOy film, or the buffer layer of the WOx film and the NbOy film is in equilibrium (junction) with the ITO layer, based on the energy (vacuum level) of electrons in the vacuum phase (0 eV) is an energy band diagram. In FIGS. 5(a) to 5(d), Φ represents a work function, and Ev represents a valence band maximum energy level (Ev) based on electron energy in a vacuum.

As can be seen from FIG. 5, a 20 nm NbOy film is thermally deposited on the WOx film, and weak doping of NbOy (intermixing at the interface between WOx and NbOy) occurs on the WOx, and the minimum energy level of the conduction band of the buffer layer (Fig. It can be seen that Ec) of 5 is closer to the Fermi energy level. As can be seen from FIG. 5, the transparent electrode according to an exemplary embodiment of the present invention can improve the internal resistance of the solar cell by having more advantageous energy band matching between the buffer layer and the ITO.

6 is a Niqui of a solar cell equipped with a transparent electrode (buffer layer-ITO) manufactured in Example 1, an electrode (Au) manufactured in Comparative Example 1, and a transparent electrode (WOx-ITO) manufactured in Comparative Example 2 It is a diagram showing Nyquist plots. As can be seen from Figure 6, it can be seen that the solar cell manufactured in Example has a resistance characteristic that is about 10 times or more lower than that of Comparative Example 2 having a single transition metal oxide film, and is almost the same as that of Au, an opaque electrode. It can be seen that it has.

Figure 7 (a) is based on the electrochemical impedance spectroscopy (EIS) measurement results of the solar cells prepared in Example 1, Comparative Example 1 and Comparative Example 2, the capacitance value according to the frequency (C≡ 1/iωZ, Z= Impedance, ω = angular frequency), and FIG. 7(b) is a diagram illustrating a trap density distribution according to an energy level E _ω calculated based on a capacitance-frequency result. In FIG. 7B, the energy level E _ω is an energy level based on a band edge (E _Bandedge ) (=0eV).

From the results of FIG. 7B, it can be seen that in the case of the transparent electrode having a structure of a single transition metal oxide film-ITO layer of Comparative Example 2, a deep trap far from the band edge is predominant. On the other hand, when the transparent electrode according to an embodiment of the present invention is provided, it can be seen that the deep trap moves toward the edge of the band, and a trap density distribution that is almost similar to that of Comparative Example 1 in which the Au electrode as an opaque electrode is provided. It can be confirmed that it has. These results indicate that when a transparent electrode according to an embodiment is provided in a solar cell, carrier density is increased, conductivity is improved (resistance is decreased), trap states are minimized, and a more improved peel is achieved. It can be interpreted as having a factor and cell efficiency.

FIG. 8 is a WOx film (WO in FIG. 8), an NbOy film (NbOz in FIG. 8), and a buffer layer (WOy/NbOz in FIG. 8) in which a WOx film and an NbOy film are stacked prepared in the same method and thickness as in Example 1. ) Of the X-ray photoelectron spectroscopy (XPS) spectrum, FIG. 8(a) shows the O 1s spectrum, FIG. 8(b) shows the W 4f spectrum, and FIG. 8(c) shows the Nd 3d spectrum. It is a drawing. Through the XPS result of FIG. 8 and elemental analysis, it was confirmed that the prepared tungsten oxide film and niobium oxide film were both in an oxygen-deficient state.

9(a) is a view showing measurement of current density-voltage graphs of each of the upper and lower cells of the tandem solar cell prepared in Example 4 and the tandem solar cell prepared in Comparative Example 3, and FIG. 9(b) Is a diagram showing the external quantum efficiency (EQE) of the upper cell (shown as a dotted line) and the lower cell (shown as a solid line) of the tandem solar cell manufactured in Example 4 and the tandem solar cell manufactured in Comparative Example 3. Table 3 shows a PERC-type Si solar cell alone (Si Cell) manufactured in the same manner as in Example 4, a tandem solar cell (WOx/NbOy) manufactured in Example 4 but not provided with an anti-reflective coating layer (AR) on the upper cell. , The tandem solar cell (WOx/NbOy-AR) prepared in Example 4 but provided with an anti-reflective coating layer (AR) on the upper cell, the short-circuit current density (J _SC ) of the tandem solar cell prepared in Comparative Example 3, and open circuit voltage (V _OC ), fill factor (FF), lower cell photoelectric conversion efficiency (η _bottom ), upper cell photoelectric conversion efficiency (η _top ), and photoelectric conversion efficiency (η _4-T ) of tandem solar cells.

(Table 3)

As can be seen from Fig. 9 and Table 3, in the 4-terminal perovskite-Si tandem solar cell, the upper cell has improved photoelectric conversion efficiency due to the smooth flow of photocurrent and the perovskite cell (solar cell) itself At the same time, it can be seen that the photoelectric conversion efficiency of the Si lower cell is improved from 6.9% to 7.1% by the upper perovskite cell provided with the transparent electrode according to the present invention. In addition, by mechanically simply laminating the perovskite cell on the top of the Si cell, the efficiency that was only 20.5% by the Si solar cell is 27.0%, and up to 27.6% when using the perovskite top cell with an anti-reflective coating layer. It can be seen that the efficiency can be increased.

As described above, the present invention has been described by the specific matters and limited embodiments and drawings, but this is provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and the present invention is Those of ordinary skill in the relevant field can make various modifications and variations from this description.

Therefore, the spirit of the present invention is limited to the described embodiments and should not be defined, and all things that are equivalent or equivalent to the claims as well as the claims to be described later fall within the scope of the spirit of the present invention. .

Claims (10)

A transparent conductive oxide layer having a first surface through which light is introduced and a second surface through which photocharges are introduced; And
Includes; a buffer layer positioned in contact with the second surface,
The buffer layer includes a first transition metal oxide layer in contact with the second surface and a second transition metal oxide layer in contact with the first transition metal oxide layer,
The first transition metal oxide has an electron affinity smaller than that of the second transition metal oxide, and the band gap energy of the first transition metal oxide is greater than the band gap energy of the second transition metal oxide. A transparent electrode provided on the side of the hole transport layer. The method of claim 1,
A transparent electrode provided on the side of the hole transport layer of a solar cell, wherein a work function of the first transition metal oxide is equal to or greater than or greater than the work function of a transparent conductive oxide and smaller than a work function of the second transition metal oxide. The method of claim 1,
The first transition metal oxide and the second transition metal oxide are each in an oxygen-deficiency state, a transparent electrode provided on the side of the hole transport layer of the solar cell. The method of claim 1,
The thickness of the first transition metal oxide film is 5 to 30 nm, and a thickness ratio obtained by dividing the thickness of the second transition metal oxide film by the thickness of the first transition metal oxide film is 3 to 20, provided on the hole transport layer side of the solar cell. Transparent electrode. The method of claim 1,
The first transition metal oxide or the second transition metal oxide is provided on the hole transport layer side of a solar cell, which is niobium oxide, zirconium oxide, molybdenum oxide, hafnium oxide, tantalum oxide, tungsten oxide, or a composite oxide thereof. Transparent electrode. The method of claim 1,
The transparent electrode is disposed in contact with the organic hole transport layer to collect light holes, a transparent electrode provided on the hole transport layer side of the solar cell. A first transparent electrode;
An electron transport layer positioned on the first transparent electrode;
A light absorbing layer positioned on the electron transport layer and including a perovskite compound;
An organic hole transport layer positioned on the light absorption layer; And
A second transparent electrode, which is a transparent electrode according to any one of claims 1 to 6, positioned on the organic hole transport layer such that the organic hole transport layer and the buffer layer are in contact with each other;
Perovskite solar cell comprising a. The method of claim 7,
Perovskite solar cell with light transmittance of 75% or more at 850nm wavelength. The method of claim 7,
The perovskite solar cell is a perovskite solar cell for an upper cell of a 4-terminal tandem solar cell. 4- Terminal tandem solar cell.

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