JP2023066887A - Tandem solar cell and manufacturing method thereof - Google Patents

Abstract

To provide a tandem solar cell capable of being manufactured at a low cost with a simple configuration and realizing high photoelectric conversion efficiency, and a manufacturing method thereof.SOLUTION: In a tandem solar cell consisting of two or more light absorption layers with different absorption wavelength ranges, at least one of the plurality of light absorption layers is a quantum dot superlattice layer composed of quantum dots forming a superlattice structure, and a tunnel junction layer is not interposed between the adjacent light absorption layers.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a tandem solar cell having a plurality of light absorbing layers and a method for manufacturing the same.

BACKGROUND ART In order to increase the power generation efficiency of a solar cell, a tandem solar cell is known that combines a plurality of light absorption layers (photoelectric conversion layers) that photoelectrically convert light in different wavelength ranges. In conventional tandem solar cells, the light absorption layers are connected by a tunnel junction layer (for example, a , Patent Document 1).

Further, in order to further increase the power generation efficiency, for example, an intermediate band type solar cell in which an intermediate band is formed by laminating a plurality of quantum dot layers in which a plurality of quantum dots are arranged in an embedded layer, and this a current adjusting solar cell formed on the light incident side of the intermediate band type solar cell, the current adjusting solar cell including a tunnel layer composed of a pn junction, and the tunnel layer forming the intermediate band type solar cell A tandem solar cell is disclosed (eg, Patent Document 2).

JP 2004-111687 A JP 2016-122752 A

However, in the tandem solar cells described in Patent Literature 1 and Patent Literature 2, since a plurality of light absorption layers having different absorption wavelength ranges are connected to each other by a tunnel junction layer, each light absorption layer It was necessary to match the total amount of carriers generated at For this reason, although the tandem structure has the effects of expanding the light absorption wavelength and increasing the open-circuit voltage, it has been difficult to increase the short-circuit current at the open-circuit voltage. In addition, the formation of the tunnel junction layer complicates the layer structure of the solar cell, which raises the problem of increased manufacturing costs.

The present invention has been proposed in view of the above problems, and aims to provide a tandem solar cell that has a simple configuration, can be manufactured at low cost, and can achieve high photoelectric conversion efficiency, and a method for manufacturing the same. aim.

In order to solve the above problems, the tandem solar cell of the present invention is a tandem solar cell formed by laminating two or more light absorbing layers having mutually different absorption wavelength ranges, Among them, at least one light absorption layer is a quantum dot superlattice layer composed of quantum dots forming a superlattice structure, and is characterized in that no tunnel junction layer is interposed between the adjacent light absorption layers.

Also, in the present invention, the quantum dots are colloidal quantum dots and contain at least one of metal sulfides, metal selenides, metal tellurides, metal arsenides, metal phosphides, and metal antimonides. You can

Further, in the present invention, the plurality of light absorption layers are arranged along the lamination direction such that the energy bands of the respective light absorption layers are arranged in a direction in which the energy of carriers passing through the light absorption layers decreases. may

Further, in the present invention, the colloidal quantum dots may have a facet plane depending on the crystal plane orientation on the surface thereof.

Further, a method for producing a tandem solar cell of the present invention is a method for producing a tandem solar cell according to each of the above items, wherein colloidal quantum dots dispersed in a solvent are allowed to settle on a substrate, and the quantum dots are It is characterized by forming a superlattice layer.

Further, in the present invention, the substrate may be a template in which a plurality of conical microholes are arranged.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the tandem-type solar cell which can be manufactured at low cost with a simple structure and can implement|achieve high photoelectric conversion efficiency, and its manufacturing method.

1 is a cross-sectional view showing a tandem solar cell according to a first embodiment of the invention; FIG. FIG. 2 is a schematic diagram showing a band diagram of the tandem solar cell of the first embodiment; FIG. 4 is a cross-sectional view showing a tandem solar cell according to a second embodiment of the invention; FIG. 5 is a schematic diagram showing a band diagram of a tandem solar cell of a second embodiment; 4 is a SEM photograph showing a template as an example of a substrate used in a method for manufacturing a tandem solar cell; 2 is a schematic diagram showing a band diagram of a tandem solar cell of Verification Example 1. FIG. FIG. 10 is a schematic diagram showing a band diagram of a tandem solar cell of Verification Example 2;

A tandem solar cell according to an embodiment of the present invention and a method for manufacturing the same will be described below with reference to the drawings. It should be noted that the embodiments shown below are specifically described for better understanding of the gist of the invention, and do not limit the invention unless otherwise specified. In addition, in the drawings used in the following description, in order to make it easier to understand the features of the present invention, there are cases where the main parts are enlarged for convenience, and the dimensional ratio of each component is the same as the actual one. not necessarily.

(Tandem solar cell: first embodiment)
FIG. 1 is a cross-sectional view showing a tandem solar cell according to a first embodiment of the invention.
A tandem solar cell (hereinafter sometimes simply referred to as a solar cell) 10 of the present embodiment comprises a front electrode 11, a back electrode 12, and a light absorbing laminate 13 formed between the two electrodes. It is configured.

Such a solar cell 10 allows sunlight to enter from the front electrode 11 side, performs photoelectric conversion in the light absorption laminate 13 , and can take out electric power generated between the front electrode 11 and the back electrode 12 .

The surface electrode 11 of the present embodiment is a comb-teeth electrode formed by forming a metal film in a comb shape and allowing sunlight to pass through the gaps between the comb-teeth portions. Ag was used as the metal film. In the case of such a comb-teeth electrode, even if sunlight is impermeable, it can be composed of a metal film having a higher conductivity than that of a transparent conductive material.

Note that the surface electrode 11 is made of a transparent conductive material capable of transmitting sunlight, for example, an electrically conductive oxide such as zinc oxide, tin oxide, and indium oxide in which oxygen defects are controlled, and zinc oxide as a main component. ATO (Sb-doped SnO ₂ ), FTO (F-doped SnO ₂ ), ITO (Sb-doped In ₂ O ₃ ), IFO (F-doped In ₂ O ₃ ), etc., which are transparent conductive films containing indium oxide as a main component, are deposited to a predetermined thickness. It can also be configured by forming a film.

It is also preferable to further form a surface protective layer (not shown) such as a transparent hard film on the outer surface side of the surface electrode 11 . By forming such a surface protective layer, the surface electrode 11 can be protected from physical stress.
It is also preferable to further form an antireflection film (not shown) between the light absorbing laminate 13 and the surface electrode 11 .

The back electrode 12 is an electrode paired with the front electrode 11 and also serves as a reflective layer that reflects the sunlight that has passed through the light absorbing laminate 13 and causes the sunlight to enter the light absorbing laminate 13 again. Therefore, for the back electrode 12, a conductive and light-reflecting metal, such as Al, an alloy containing Al, Ag, or an alloy containing Ag, should be used. is preferred.

The light-absorbing laminate 13 of this embodiment includes a plurality of light-absorbing layers, that is, a first light-absorbing layer 14, a second light-absorbing layer 15, and a third light-absorbing layer 16, which are stacked in order from the surface electrode 11 side. Become. The first light absorption layer 14, the second light absorption layer 15, and the third light absorption layer 16 are made of materials having absorption wavelength ranges different from each other. The first light absorption layer 14, the second light absorption layer 15, and the third light absorption layer 16 are laminated without interposing a tunnel junction layer therebetween.

The first light absorption layer 14 is composed of nanosheets of tin (II) selenide (SnSe) (with a thickness of several tens to several hundred nanometers). Among the plurality of light absorption layers 14, 15, and 16, the first light absorption layer 14 absorbs sunlight in the wavelength region on the short wavelength side and performs photoelectric conversion.

The second light absorption layer 15 is a quantum dot superlattice layer (band edge absorption wavelength: 1800 nm) composed of quantum dots of lead sulfide (PbS), which is a semiconductor that forms a superlattice structure. A quantum dot superlattice layer in which such semiconductor quantum dots are regularly arranged has physical properties as a quantum dot aggregate that are different from independent individual quantum dots due to interactions between adjacent quantum dots.

In particular, when the distance between quantum dots is close to 5 nanometers or less, coupling of wave functions (spreading of electrons) between quantum dots occurs, which is called quantum resonance. These quantum resonances spread electronic states throughout the ensemble, greatly enhancing charge mobility.

For example, when the quantum dots are arranged periodically, the wave function maintains a specific energy state as a standing wave in the entire quantum dot assembly. This particular energy state is called the intermediate band. Also, such an aggregate of quantum dots is called a quantum dot superlattice. Electrons in the intermediate band can move within the superlattice very well. A plurality of such intermediate bands are formed based on the ground level and the excited level when the quantum dot is isolated.

In order to form the quantum dot superlattice and the resulting intermediate band, it is necessary to arrange the quantum dots as uniformly as possible, three-dimensionally and periodically, as well as possible. For example, Patent Literature 2 mentioned above discloses an example of fabricating a quantum dot superlattice by vapor phase epitaxial growth of a III-V group semiconductor.

However, the quantum dots in the vapor phase epitaxial growth method as in Patent Document 2 are based on the crystal strain during growth due to lattice mismatch with the substrate, so the crystal strain that changes every moment during growth. It is known that control is difficult and there is a limit to forming a superlattice layer in which uniform quantum dots are periodically arranged.

The third light absorption layer 16 is composed of a single crystal silicon layer. Such a third light absorption layer 16 absorbs sunlight in the wavelength region on the long wavelength side among the plurality of light absorption layers 14, 15, and 16, and performs photoelectric conversion.

FIG. 2 is a schematic diagram showing a band diagram of the tandem solar cell of this embodiment shown in FIG.
In the light-absorbing laminate 13 of the solar cell 10 of this embodiment, the upper end of each bandgap is 3.74 eV, 4.2 eV, and 4.05 eV in order from the first light-absorbing layer 14, but the second light-absorbing layer 14 Since the light-absorbing layer 15 is a quantum dot superlattice layer, an intermediate band is formed at an energy position higher than 4.2 eV in the second light-absorbing layer 15 . A potential barrier (a barrier that cannot be crossed without obtaining energy when carriers try to flow toward the electrode) is not formed. The same can be said for holes.

In this way, the energy bands of the respective light absorption layers 14, 15, 16 along the lamination direction are aligned in the direction in which the energy of carriers passing through the light absorption layers decreases, thereby allowing electrons and positive electrons to pass through the light absorbing layers. The holes flow smoothly toward the back electrode 12 and the surface electrode 11 .

The quantum dot superlattice layer forming the second light absorption layer 15 is different from a mere quantum dot light absorption layer. In a conventional quantum dot light absorption layer, although an excitation level exists in a single quantum dot, it is isolated and does not form an energy band. Therefore, mere excited levels do not help carrier flow. For example, when a quantum dot light absorption layer in which quantum dots do not form a superlattice is used as the second light absorption layer 15, a potential barrier is generated, so it is necessary to insert a tunnel junction layer between the light absorption layers. occur.

The formation position of the intermediate band in such a quantum dot superlattice layer (the second light absorption layer 15 in this embodiment) can be adjusted to any position depending on the material and size of the quantum dots.

For example, the constituent material of the quantum dot superlattice layer may contain at least one of metal sulfide, metal selenide, metal telluride, metal arsenide, metal phosphide, and metal antimonide. More specifically, for example, PbS, CdS, CdSe, CdTe, GaAs, GaSb, HgSe, HgTe, InAs, InP, InSb, PbSe, PbTe, ZnS, ZnSe, ZnTe, Ag ₂ S, SnSe, SnTe, or these can be composed of a mixture of

The quantum dot superlattice layer forming the second light absorption layer 15 can form a quantum dot superlattice using the constituent materials described above, for example, by a vapor phase epitaxial growth method. Colloidal quantum dots can also be used as quantum dots for realizing a better superlattice. Colloidal quantum dots can be made by chemical reactions in liquids. Colloidal quantum dots can be formed without being bound by a substrate, unlike the vapor phase epitaxial growth method, so highly uniform quantum dots can be obtained.

Furthermore, by adjusting the size of the ligands surrounding the colloidal quantum dots, it is possible to control the closest distance between adjacent quantum dots. Moreover, it can be manufactured in large quantities at low cost. When colloidal quantum dots are precipitated and laminated on a substrate in a solvent, the quantum dots are closely packed to form a quantum dot superlattice layer as a three-dimensional periodic structure.

The surface of colloidal quantum dots can also have facets depending on the crystal plane orientation. The facet plane has the function of aligning the crystal plane orientation of each quantum dot in the same direction when the colloidal quantum dots are sedimented and stacked in a solvent to form a quantum dot superlattice layer. When the crystal plane orientation of each quantum dot is aligned, the wave function coupling between the quantum dots becomes favorable, and an intermediate band with excellent electrical characteristics is formed.

On the other hand, the three-dimensional periodic structure produced by sedimenting colloidal quantum dots in a solvent is a uniform periodic structure in a narrow area of the field of view of an electron microscope, but when viewed in a wider area, it is arranged. The direction is chaotic. The reason for this is that the colloidal quantum dots are arranged randomly and simultaneously.

In order to solve these problems and align the alignment direction in a wider area, it is possible to use a substrate processed to forcibly align the alignment direction instead of a planar substrate on which the colloidal quantum dots can move chaotically. . Such a processed substrate can be produced by anisotropic etching or the like in which the etching rate depends on the crystal plane orientation of the substrate.

Another advantage of using colloidal quantum dots rather than quantum dots by vapor phase epitaxial growth is the flexibility of material selection. In the vapor phase epitaxial growth method, the materials that can be used are naturally limited due to the need to be nearly lattice-matched with the substrate used for crystal growth, but this is not the case when colloidal quantum dots are used. As a result, when designing the band diagram of the tandem solar cell, it becomes possible to completely eliminate the restriction on material selection, and the constituent materials can be freely selected.

As described above, according to the solar cell 10 of the present embodiment, the second light absorbing layer 15 among the light absorbing layers 14, 15, and 16 constituting the light absorbing laminate 13 is a quantum dot superlattice layer. can form an intermediate band at an arbitrary position and eliminate the potential barrier. This allows carriers to move smoothly toward the electrode without forming a tunnel junction layer. As a result, a current matching condition is not required when designing the solar cell 10, and the voltage between the electrodes and the generated current can be improved at the same time. As a result, a highly efficient solar cell can be realized. Moreover, since the intermediate band can be formed at an arbitrary position, the degree of freedom in designing each light absorption layer can be greatly improved.

(Tandem solar cell: Second embodiment)
FIG. 3 is a cross-sectional view showing a tandem solar cell according to a second embodiment of the invention. Moreover, FIG. 4 is a schematic diagram showing a band diagram of the tandem solar cell of FIG.
The solar cell 20 of the present embodiment is formed by stacking a front electrode 21, a hole transport layer 24, a light absorbing laminate 23, and a back electrode 22 in order from the sunlight incident side. The light-absorbing laminate 23 is composed of a first light-absorbing layer 25 and a second light-absorbing layer 26 .

The rear surface electrode 22 of this embodiment is an aluminum substrate. The surface electrode 21 is formed by forming a film of ITO, which is a transparent conductive material capable of transmitting sunlight, with a predetermined thickness.

The hole transport layer 24 is a layer that allows holes to flow smoothly toward the surface electrode 21 and blocks the inflow of electrons. The hole transport layer 24 of this embodiment is composed of a mixture of poly(3,4-ethylenedioxythiophene):(PEDOT) and poly(4-styrenesulfonic acid):(PSS).

The first light absorption layer 25 is a quantum dot superlattice layer (band edge absorption wavelength 1400 nm) composed of quantum dots of lead sulfide (PbS), which is a semiconductor forming a superlattice structure. The first light absorbing layer 25, which consists of a quantum dot superlattice layer of PbS, forms an intermediate band in which electrons in a quantum dot can move to other adjacent quantum dots. Among the plurality of light absorption layers 25 and 26, the first light absorption layer 25 absorbs sunlight in the wavelength region on the short wavelength side and performs photoelectric conversion.

The second light absorption layer 26 is a quantum dot superlattice layer (band edge absorption wavelength 1800 nm) composed of quantum dots of lead sulfide (PbS), which is a semiconductor forming a superlattice structure. The second light absorbing layer 26, which consists of a quantum dot superlattice layer of PbS, forms an intermediate band in which electrons in a quantum dot can move to other adjacent quantum dots. Such a second light absorption layer 26 absorbs sunlight in the wavelength region on the longer wavelength side among the plurality of light absorption layers 25 and 26, and performs photoelectric conversion.

In the light-absorbing laminate 23 of the solar cell 20 of this embodiment, the upper ends of the respective band gaps are 4.1 eV and 4.2 eV in order from the first light-absorbing layer 25, but the first light-absorbing layer 25 Since the quantum dot superlattice layer is used for both the light absorbing layer 26 and the second light absorbing layer 26, an intermediate band is formed at an energy position higher than the energy band edge of each of the first light absorbing layer 25 and the second light absorbing layer 26. be. Thereby, no potential barrier is formed in any of the light absorbing laminates 23 . Therefore, electrons smoothly flow toward the electrodes. The same can be said for holes.

(Manufacturing method of tandem solar cell)
As a method for producing a tandem solar cell, when forming a quantum dot superlattice layer, a quantum dot dispersion in which colloidal quantum dots are dispersed in a solvent such as toluene (hereinafter referred to as QD (Quantum Dot) dispersion) can be used to form the quantum dots in this QD dispersion by sedimentation onto the substrate.

As such a substrate, as shown in FIG. 5, a template 100 in which a plurality of conical microholes 101, 101 . . . are arranged can be used. The template 100 is formed by, for example, using a silicon substrate and forming 3 μm-square, 3 μm-deep, quadrangular pyramid-shaped microholes 101 , 101 , . . . can be used.

These conical microholes 101, for example, have a silicon single crystal substrate and use a potassium hydroxide (KOH) solution as an etching solution. It is possible to form uniform microholes in which the plane orientation of the substrate appears.

By dropping the QD dispersion onto such a template 100 or dipping the template into the QD dispersion to allow the quantum dots to settle within the respective microholes 101 and subsequently or simultaneously evaporating the solvent, the quantum dots A superlattice layer can be formed.

Here, the time required for the sedimentation of quantum dots varies depending on the type of solvent and QDs. It is preferable to allow the QDs to settle for as long as possible because close packing of the QDs is achieved and a periodic three-dimensional array is formed by the QDs settling in the most mechanically stable location on the substrate. . The required settling time and 3D array integrity are also affected by the affinity of the substrate to the solvent and QDs. That is, the sedimentation time can be selected by weighing the cost of production, which is lower with shorter time, and the integrity of the sequence, which is improved with longer time. For example, when using PbS quantum dots with toluene as the solvent and oleic acid as the ligand, the typical settling time is about 3 days to 1 week.

Although embodiments of the invention have been described above, such embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

(Verification example 1)
The effects of the present invention have been verified.
As Verification Example 1, the performances of the solar cells of Inventive Example 1 and Comparative Examples 1 and 2 were calculated in the case where the light-absorbing laminate was composed of two layers.

As Example 1 of the present invention, an Au film was used as the front electrode (positive electrode) and an Al film was used as the back electrode (negative electrode). A quantum dot superlattice layer (band edge absorption wavelength: 1400 nm) composed of quantum dots of lead sulfide (PbS), which is a semiconductor constituting the structure, was laminated in this order.

As Comparative Example 1, instead of the quantum dot superlattice layer of Inventive Example 1, a quantum dot light absorption layer having no superlattice structure was used.
As Comparative Example 2, a device in which a tunnel junction layer was formed between the light absorbing layer made of nanowires of Comparative Example 1 and the quantum dot light absorbing layer was used.
FIG. 6 shows band diagrams of the solar cells of Inventive Example 1 and Comparative Examples 1 and 2. In FIG.

In Example 1 of the present invention shown in FIG. 6A, a quantum dot superlattice layer is used as the light absorbing laminate, so that an intermediate band is formed, and electrons and holes, which are carriers, each have two layers of light absorbing layers. flows smoothly from the positive electrode to the negative electrode.

On the other hand, in Comparative Example 1, between the light absorption layer made of nanowires and the quantum dot light absorption layer that does not have a superlattice structure, a large amount of heat is generated for electrons due to a large energy difference, and a large amount of heat is generated for holes. The barrier does not allow current to flow and does not function as a tandem solar cell. In Comparative Example 2, which eliminates such a potential barrier, the electrons in the conductor of the light absorption layer made of nanowires and the holes in the valence band of the quantum dot light absorption layer are recombined by the tunnel junction layer, whereby the current is Heat generation due to current flow can also be suppressed, but it is necessary to perform a design that satisfies the current matching condition so that recombination does not generate surplus carriers.

Next, the outputs of the solar cells of Inventive Example 1 and Comparative Example 2 that actually function as tandem solar cells were calculated. In the calculation, the current generation capacity of the quantum dot superlattice layer of Inventive Example 1 was set to 40 mA/cm ² in consideration of the light absorption by the intermediate band, the current generation capacity of the light absorption layer made of SnSe nanowires was set to 10 mA/cm ² , The current generation capacity of the quantum dot light absorption layer having no superlattice structure in Comparative Example 2 was set to 15 mA/cm ² .

In Example 1 of the present invention, the open-circuit voltage (V1) is determined by the difference in work function between the positive electrode and the negative electrode, and is 1.04V. Also, the short-circuit current density (D1) is 50 mA/cm ² because it is determined by the total current generated in the entire light-absorbing laminate. When the fill factor is set to 0.8, the output of the solar cell of Inventive Example 1 is V1×D1×0.8=41.06 mA/cm ² .

On the other hand, in Comparative Example 2, the open circuit voltage (V1) is 1.04V. In addition, the short-circuit current density (D1) is the current matching condition, so that the current generated in the quantum dot light absorption layer without a superlattice structure is equal to the current generated in the SnSe nanowire light absorption layer, which has a small current generating ability. need to be adjusted. As a result, the short circuit current density (D1) is 10 mA/cm ² . When the fill factor is set to 0.8, the output of the solar cell of Comparative Example 2 is V1×D1×0.8=8.32 mA/cm ² .

From the results of Verification Example 1 described above, the solar cell of Example 1 of the present invention using the quantum dot superlattice layer as the light absorption layer is a comparison using a quantum dot light absorption layer that has the same configuration but does not have a superlattice structure as the light absorption layer. Compared with the solar cell of Example 2, the output was improved by about 4.9 times. The effects of the present invention have been confirmed.

(Verification example 2)
As Verification Example 2, the performances of the solar cells of Invention Example 2 and Comparative Examples 3 and 4 were calculated in the case where the light-absorbing laminate was composed of three layers.

As Example 2 of the present invention, an Au film was used as the front electrode (positive electrode) and an Al film was used as the back electrode (negative electrode). A light absorption layer, a quantum dot superlattice layer (band edge absorption wavelength 1800 nm) made of quantum dots of lead sulfide (PbS), which is a semiconductor forming a superlattice structure, and an n-type single crystal silicon layer are laminated in this order. I used what I did.

As Comparative Example 3, instead of the quantum dot superlattice layer of Inventive Example 2, a quantum dot light absorption layer having no superlattice structure was used.
As Comparative Example 4, a tunnel junction layer was provided between the SnSe nanowire light absorbing layer and the PbS quantum dot light absorbing layer of Comparative Example 3 and between the PbS quantum dot light absorbing layer and the n-type single crystal silicon layer. The formed one was used.
FIG. 7 shows band diagrams of the solar cells of Inventive Example 2 and Comparative Examples 3 and 4. In FIG.

In Example 2 of the present invention shown in FIG. 7( a ), an intermediate band is formed by using a PbS quantum dot superlattice layer as the light absorbing laminate, and electrons and holes, which are carriers, each have three layers of light absorbing layers. flows smoothly from the positive electrode to the negative electrode.

On the other hand, in Comparative Example 3, a potential barrier was formed against both electrons and holes between the PbS quantum dot light absorption layer, which does not have a superlattice structure, and the n-type single crystal silicon layer, and no current flowed. , does not work as a tandem solar cell. In Comparative Example 4, in which such potential barriers are eliminated, the tunnel junction layers provide a tunnel junction layer between the SnSe quantum dot light absorption layer and the PbS quantum dot light absorption layer, and between the PbS quantum dot light absorption layer and the n-type single crystal silicon layer. Therefore, it is necessary to design current matching conditions so that recombination of electrons in the conductor and holes in the valence band causes current to flow, but the recombination does not cause surplus of carriers. is.

Next, the outputs of the solar cells of Inventive Example 2 and Comparative Example 4, which actually function as tandem solar cells, were calculated. In the calculation, the current generation capacity of the SnSe nanowire light absorption layer of Inventive Example 2 is 10 mA/cm ² , the current generation capacity of the quantum dot superlattice layer is 40 mA/cm ² considering the light absorption by the intermediate band, and the comparative example. 4, the current generating capacity of the quantum dot light absorbing layer that does not have a superlattice structure is 15 mA/cm ² , and the current generating capacity of the n-type single crystal silicon layer is 25 mA/cm 2 , which is a value typically known as the performance of silicon solar cells. cm ² respectively.

In Example 2 of the present invention, the open-circuit voltage (V1) is determined by the difference in work function between the positive electrode and the negative electrode, and is 1.04V. Also, the short-circuit current density (D1) is 75 mA/cm ² because it is determined by the total current generated in the entire light-absorbing laminate. Then, when the fill factor is set to 0.8, the output of the solar cell of Inventive Example 2 is V1×D1×0.8=62.4 mA/cm ²

On the other hand, in Comparative Example 4, the open circuit voltage (V1) is 1.04V. In addition, the short-circuit current density (D1) satisfies the current matching condition, so that the PbS quantum dot light absorption layer and the n-type single crystal silicon are matched to the generated current of the SnSe nanowire light absorption layer, which has the lowest current generating ability. It is necessary to adjust the layer generation current. As a result, the short circuit current density (D1) is 10 mA/cm ² . When the fill factor is set to 0.8, the output of the solar cell of Comparative Example 2 is V1×D1×0.8=8.32 mA/cm ² .

From the results of Verification Example 2 described above, the solar cell of Example 2 of the present invention using the quantum dot superlattice layer as the light absorption layer is a comparison using a quantum dot light absorption layer that has the same configuration but does not have a superlattice structure as the light absorption layer. Compared with the solar cell of Example 4, the output was greatly improved by about 7.5 times. The effects of the present invention have been confirmed.

DESCRIPTION OF SYMBOLS 10, 20... Solar cell 11, 21... Surface electrode 12, 22... Back electrode 13, 23... Light absorption layered product 14... First light absorption layer 15, 26... Second light absorption layer (quantum dot superlattice layer)
16... Third light absorption layer 24... Hole transport layer 25... First light absorption layer (quantum dot superlattice layer)

Claims (6)

A tandem solar cell formed by laminating two or more light absorption layers having mutually different absorption wavelength ranges,
At least one of the plurality of light absorption layers is a quantum dot superlattice layer composed of quantum dots forming a superlattice structure,
A tandem solar cell, wherein no tunnel junction layer is interposed between the light absorption layers adjacent to each other. 4. The quantum dot is a colloidal quantum dot and contains at least one of metal sulfide, metal selenide, metal telluride, metal arsenide, metal phosphide, and metal antimonide. 2. The tandem solar cell according to 1. The plurality of light absorption layers are arranged along the lamination direction such that the energy bands of the respective light absorption layers are arranged in a direction in which the energy of carriers passing through the light absorption layers decreases. Item 3. The tandem solar cell according to Item 1 or 2. 4. The tandem solar cell according to any one of claims 1 to 3, wherein the colloidal quantum dots have facet planes depending on the crystal plane orientation on their surfaces. A method for manufacturing the tandem solar cell according to any one of claims 1 to 4,
A method for producing a tandem solar cell, comprising precipitating colloidal quantum dots dispersed in a solvent onto a substrate to form the quantum dot superlattice layer. 6. The method of manufacturing a tandem solar cell according to claim 5, wherein the substrate is a template in which a plurality of conical microholes are arranged.

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