PEROVSKITE SOLAR CELL AND PHOTOVOLTAIC MODULE

A perovskite solar cell includes a perovskite layer comprising a first surface and a second surface that are opposite each other in the thickness direction thereof; a hole transport layer provided on the first surface; and an electron transport layer provided on the second surface. The electron transport layer comprises at least two sub-layers and a doping material, and each of the sub-layers has a conduction band bottom energy level lower than that of the hole transport layer and a valence band top energy level lower than that of the hole transport layer.

TECHNICAL FIELD

The present application relates to the technical field of solar cells, in particular to a perovskite solar cell and a photovoltaic module.

BACKGROUND ART

Perovskite solar cells are solar cells with an organic metal halide perovskite material as a light absorption layer, which have excellent photovoltaic properties and can be prepared by simple methods, bringing new space and hope to photovoltaic power generation.

In the production process of perovskite solar cells, how to further improve the photoelectric conversion efficiency thereof is an urgent problem to be solved.

SUMMARY

The embodiments of the present application provide a perovskite solar cell and a photovoltaic module, and the photoelectric conversion efficiency of the perovskite solar cell can be improved.

An embodiment of the first aspect of the present application provides a perovskite solar cell comprising a perovskite layer, a hole transport layer and an electron transport layer, wherein the perovskite layer comprises a first surface and a second surface that are opposite each other in the thickness direction thereof; the hole transport layer is provided on the first surface; and the electron transport layer is provided on the second surface, the electron transport layer comprises at least two sub-layers and a doping material, and each of the sub-layers has a conduction band bottom energy level lower than that of the hole transport layer and a valence band top energy level lower than that of the hole transport layer.

A second aspect of the present application provides a photovoltaic module, comprising a perovskite solar cell according to any embodiment of the first aspect of the present application.

In the drawings, the figures are not necessarily drawn to scale.

Reference signs in the drawings are as follows:X, thickness direction;10, perovskite layer;10a, first surface;10b, second surface;20, hole transport layer;30, electron transport layer;31, first sub-layer;32, second sub-layer;33, third sub-layer;40, first electrode;50, second electrode.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the perovskite solar cell and the photovoltaic module of the present application are disclosed in detail appropriately with reference to the detailed description of the drawings. However, unnecessary detailed illustrations may be omitted in some instances. For example, there are situations where detailed description of well-known items and repeated description of actually identical structures are omitted. This is to prevent the following description from being unnecessarily verbose, and facilitates understanding by those skilled in the art. Moreover, the accompanying drawings and the descriptions below are provided for enabling those skilled in the art to fully understand the present application, rather than limiting the subject matter disclosed in the claims.

The “ranges” disclosed in the present application are defined in the form of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits defining the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it should be understood that the ranges 60-110 and 80-120 are also contemplated. Additionally, if minimum range values 1 and 2 are listed and maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless stated otherwise, the numerical range “a-b” denotes an abbreviated representation of any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range “0-5” means that all the real numbers between “0-5” have been listed herein, and “0-5” is just an abbreviated representation of combinations of these numerical values. In addition, when a parameter is expressed as an integer≥2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

All the embodiments and optional embodiments of the present application can be combined with one another to form new technical solutions, unless otherwise stated.

All the technical features and optional technical features of the present application can be combined with one another to form a new technical solution, unless otherwise stated.

Unless otherwise stated, all the steps of the present application may be performed sequentially or randomly, in some embodiments sequentially. For example, the method including steps (a) and (b) indicates that the method may comprise steps (a) and (b) carried out sequentially, and may also comprise steps (b) and (a) carried out sequentially. For example, reference to “the method may further comprise step (c)” indicates that step (c) may be added to the method in any order, e.g., the method may comprise steps (a), (b) and (c), steps (a), (c) and (b), or steps (c), (a) and (b).

The terms “comprise” and “include” mentioned in the present application are open-ended or may also be closed-ended, unless otherwise stated. For example, “comprise” and “include” may mean that other components not listed may or may not further be comprised or included.

In the present application, the term “or” is inclusive unless otherwise specified. For example, the phrase “A or B” means “A, B, or both A and B”. More specifically, the condition “A or B” is satisfied by any one of the following: A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present). In this disclosure, the phrases “at least one of A, B, and C” and “at least one of A, B, or C” both mean only A, only B, only C, or any combination of A, B, and C.

A perovskite solar cell comprises a perovskite layer, a hole transport layer, an electron transport layer, and an electrode. The working process of a perovskite cell mainly includes: generation and separation of excitons, transport of free carriers, collection of carriers, and generation of current. The specific process is as follows: the perovskite layer in a perovskite solar cell absorbs photons from sunlight to generate excitons. Since the perovskite layer has low coulomb force binding, excitons are then separated into free electrons and holes. The separated free carriers are transported in the perovskite layer and transported through transport layers. The electron transport layer plays a role in transporting electrons and blocking holes, while the hole transport layer plays a role in transporting holes and blocking electrons. The electrons and holes transported through the transport layers are respectively collected by electrodes to form current and voltage.

In addition, in the working process of a perovskite cell, carrier recombination will occur at the interface between the perovskite layer and the transport layers, which will seriously affect the efficiency of perovskite solar cells.

In order to improve the photoelectric conversion efficiency of perovskite solar cells, the inventors improve a perovskite solar cell by adjusting and controlling the energy level structure by means of bulk doping. Adjusting and controlling the energy level structure can reduce the recombination of photon-generated carriers to a certain extent and improve the extraction and transport efficiency of electrons, thereby increasing the open circuit voltage and current.

An embodiment of the first aspect of the present application provides a perovskite solar cell.

FIG.1shows the structural schematic diagram of a perovskite solar cell provided by some embodiments of the present application. As shown inFIG.1, the perovskite solar cell comprises a perovskite layer10, a hole transport layer20, and an electron transport layer30. The perovskite layer10comprises a first surface10aand a second surface10bthat are opposite each other in the thickness direction X thereof. The hole transport layer20is provided on the first surface10a. The electron transport layer30is provided on the second surface10b, the electron transport layer30comprises at least two sub-layers30aand the electron transport layer30comprises a doping material, wherein each of the sub-layers30ahas a conduction band bottom energy level lower than that of the hole transport layer20, and each of the sub-layers30ahas a conduction band bottom energy level lower than the valence band top energy level of the hole transport layer20.

The energy level structure of the perovskite solar cell according to an embodiment of the present application is adjusted and controlled by doping the electron transport layer30with a doping material, such that the conduction band bottom energy level of each of the sub-layers30ain the electron transport layer30is lower than that of the hole transport layer20, the valence band top energy level of each of the sub-layers30ais lower than that of the hole transport layer20, and there is a difference between the energy levels of each of the sub-layers30aand the hole transport layer20. The presence of such a difference between the energy levels can ensure the formation of a built-in electric field in the perovskite solar cell and the efficient transport of carriers. Meanwhile, the difference between the conduction band bottom energy levels can ensure the unidirectional transport of electrons, and the difference between the valence band top energy levels can ensure the unidirectional transport of holes, which can effectively improve the photoelectric conversion efficiency of the perovskite solar cell. In addition, according to an embodiment of the present application, the migration of halogens in the perovskite layer10can be inhibited, which improves the structural stability of the perovskite solar cell.

A larger difference between the energy levels of each of the sub-layers30aand the hole transport layer20can further ensure the formation of a built-in electric field in the perovskite solar cell and the efficient transport of carriers.

In some embodiments, the difference between the conduction band bottom energy levels of the sub-layer30aof the electron transport layer30that is close to the second surface10band the perovskite layer10is −1.0 eV-1.0 eV. Optionally, the difference between the conduction band bottom energy levels of the sub-layer30aof the electron transport layer30that is close to the second surface10band the perovskite layer10is −0.3 eV-0.3 eV. With the difference between the energy levels of the sub-layer30aof the electron transport layer30that is close to the second surface10band the perovskite layer10satisfying the numerical range above, the electron transport efficiency can be improved. Moreover, with the difference between the conduction band bottom energy levels in the range above, the recombination of photon-generated carriers can be reduced, thereby increasing the open circuit voltage and current.

In some embodiments, the valence band top energy level of the sub-layer30aof the electron transport layer30that is close to the second surface10bis lower than that of the perovskite layer10. The valence band top energy level of the sub-layer30aof the electron transport layer30that is close to the second surface10bcan more effectively block the holes from the perovskite layer10, which can avoid the recombination of a hole and an electron to a certain extent to reduce the current of the perovskite solar cell.

In some embodiments, the difference between the Fermi levels of the sub-layer30aof the electron transport layer30that is close to the second surface10band the perovskite layer is 10≤1.5 eV, and with the difference in the above range, it can be ensured that the electron transport layer30is electron-conductive, thereby improving the electron transport efficiency.

Barriers may be formed on transport channels for carriers due to severe band bending, which affects the performance of perovskite solar cells. In some embodiments, the difference between the conduction band bottom energy level and the Fermi level of the sub-layer30aof the electron transport layer30that is close to the second surface10bis ≤1.5 eV, and with the difference in the range above, unnecessary band bending between the electron transport layer30and the perovskite layer10can be reduced, which improves the transport efficiency of carriers, thereby improving the photoelectric conversion efficiency of the perovskite solar cell.

In some embodiments, the difference between the conduction band bottom energy level and the valence band top energy level of the sub-layer30aof the electron transport layer30that is close to the second surface10bis ≥1.5 eV, and the sub-layer satisfying the above numerical range has a larger band gap, which can filter ultraviolet light, thereby avoiding the damage of ultraviolet light to the perovskite layer10.

As a transport layer, the electron transport layer30can effectively transport electrons and reduce the carrier recombination at the interface between the perovskite layer10and the electron transport layer30, thereby improving the photoelectric conversion efficiency of the perovskite solar cell.

In an embodiment of the present application, the electron transport layer30comprises at least two sub-layers30a.

As an example, the electron transport layer30comprises two sub-layers30a, namely a first sub-layer31and a second sub-layer32, respectively; or the electron transport layer30comprises three sub-layers30a, namely a first sub-layer31, a second sub-layer32, and a third sub-layer33, respectively; or the electron transport layer30comprises four sub-layers, namely a first sub-layer31, a second sub-layer32, a third sub-layer33, and a fourth sub-layer, respectively, and so forth. The above description of electron transport layer30is only for illustrative purposes and is not intended to limit the specific number of layers of the electron transport layer30.

FIG.2shows the structural schematic diagram of a perovskite solar cell provided by some embodiments of the present application. As shown inFIG.2, in some embodiments, the electron transport layer30comprises three sub-layers, namely a first sub-layer31, a second sub-layer32, and a third sub-layer33, respectively. The first sub-layer31, the second sub-layer32, and the third sub-layer33are stacked sequentially in the direction away from the second surface10b. The first sub-layer31is provided close to the perovskite layer10, the third sub-layer33is provided away from the perovskite layer10, and the second sub-layer32is provided between the first sub-layer31and the third sub-layer33. The electron transport layer30comprising three sub-layers enables the flexible adjustment and control of the energy level of each layer, which is conducive to improving the extraction efficiency and transport efficiency of carriers.

The first sub-layer31is a tin oxide layer comprising a first doping material. The first doping material comprises an alkali metal, an alkaline earth metal, a transition metal, a poor metal, a metalloid, a non-metallic element, an ionic liquid, a carboxylic acid, a phosphoric acid, a carbon derivative, a self-assembled single molecule or an organic polymer. The tin oxide layer has not only good energy level alignment but also high mobility itself, enabling efficient electron extraction and transport. By doping the first sub-layer31with a first doping material, the first doping material can adjust and control the energy levels of the first sub-layer31and passivate the bulk phase defects of the material, which can increase the concentration and mobility of carriers, thereby improving the photoelectric conversion efficiency of the perovskite solar cell.

By selecting the first doping material, the energy levels of the electron transport layer30can be effectively improved, and the energy level structure of the perovskite cell can be adjusted. Next, the first doping material is illustrated with specific examples.

As some examples of the alkali metal, the alkali metal includes at least one of Li, K, Na, Rb and Cs.

As some examples of the alkaline earth metal, the alkaline earth metal includes at least one of Be, Sr and Ba.

As some examples of the poor metal, the poor metal includes at least one of Al, Ga, In, Sn, Tl, Pb and Bi.

As some examples of the metalloid, the metalloid includes at least one of B, Si, Ge, As, Sb and Te.

As some examples of the non-metallic element, the non-metallic element includes at least one of F, Cl, Br, I, P, S and Se.

As some examples of the ionic liquid, the ionic liquid includes at least one of 1-butyl-3-methylimidazolium tetrafluoroborate, ammonium chloride, ammonium sulfide, tetramethylammonium hydroxide and 2,2,2-trifluoroethanol.

As some examples of the carboxylic acid, the carboxylic acid includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, 4-imidazoleacetic acid hydrochloride, and acetic acid.

As some examples of the carbon derivative, the carbon derivative includes at least one of carbon quantum dots, carbon nanotubes, graphene, carbon 60, carbon 60 derivatives, graphitic carbon nitride and carbon 9.

As some examples of the self-assembled single molecule, the self-assembled single molecule includes at least one of 4-pyridinecarboxylic acid, dopamine, 3-aminopropyltriethoxysilane and glycine.

As some examples of the organic polymer, the organic polymer includes at least one of polystyrene, polyethylenimine ethoxylated, polyethylene oxide, and triphenylphosphine oxide.

The second sub-layer32includes an imide compound layer, a quinone compound layer, a fullerene layer, a perovskite oxide layer, a fluoride layer, or an oxide layer. The first sub-layer31and the second sub-layer32synergize with each other, which can effectively improve the energy level structure of the electron transport layer30.

As some examples of the imide compound layer, the imide compound layer comprises an imide compound or a derivative of the imide compound, and the imide compound includes phthalamide, succinimide, N-bromosuccinimide, glutarimide or maleimide.

As some examples of the quinone compound layer, the quinone compound layer comprises a quinone compound or a derivative of the quinone compound, and the quinone compound includes benzoquinone, naphthoquinone, phenanthrenequinone or anthraquinone.

As some examples of the perovskite oxide layer, the perovskite oxide layer comprises strontium titanate, calcium titanate, barium titanate, lithium titanate, iron(II) titanium oxide, nickel titanate or cobalt titanate.

As some examples of the fluoride layer, the fluoride layer comprises lithium fluoride or calcium fluoride.

The third sub-layer33comprises a metal oxide layer or a metal oxide layer comprising a second doping material, and the metal oxide layer includes a SnO2layer, a In2O3layer, a ZnO layer, a CdO layer, a NiO layer, a CdIn2O4layer, a Cd2SnO4layer, a Zn2SnO4layer, a MgIn2O4layer, a ZnIn2O4layer, a CoIn3O6layer, a ZnV2O6layer, a CuAlO2layer, or a CuGaO2layer. The first sub-layer31, the second sub-layer32, and the third sub-layer33synergize with each other, which can effectively improve the energy level structure of the electron transport layer30.

As some examples of the SnO2layer, the SnO2layer comprises a second doping material, the element of which comprises at least one of F, Sb, P, As, Te and Cl.

As some examples of the In2O3layer, the In2O3layer comprises a second doping material, the element of which comprises at least one of W, Mn, Zr, Ti, Sb, F and Ag.

As some examples of the ZnO layer, the ZnO layer comprises a second doping material, the element of which comprises at least one of Ga, In, F, N, B and Al.

As a transport layer, the hole transport layer20can effectively transport holes and reduce the carrier recombination at the interface between the perovskite layer10and the hole transport layer20, thereby improving the photoelectric conversion efficiency of the perovskite solar cell. The material of the hole transport layer20can be selected from conventional material in the art, which is not limited herein.

As an absorbing layer of light, the perovskite layer10can convert photons into holes and electrons and the material thereof can be selected from conventional material in the art, which is not limited herein.

The perovskite solar cell according to an embodiment of the present application further comprises a first electrode and a second electrode. At least one of the first electrode and the second electrodes is a transparent electrode. As an example, the transparent electrode is an FTO conductive glass electrode.

FIG.3shows the structural schematic diagram of a perovskite solar cell provided by some embodiments of the present application. As shown inFIG.3, the perovskite solar cell comprises a first electrode40, a hole transport layer20, a perovskite layer10, an electron transport layer30and a second electrode50, which are stacked sequentially in the thickness direction X thereof, wherein the electron transport layer30comprises a first sub-layer31, a second sub-layer32, and a third sub-layer33.

[Method for Preparing Perovskite Solar Cell]

A second aspect of the present application provides a method for preparing a perovskite solar cell, which is used to prepare the perovskite solar cell of the first aspect of the present application, with each of the sub-layers of the electron transport layer of the prepared perovskite solar cell having a conduction band bottom energy level lower than that of the hole transport layer and a valence band top energy level lower than that of the hole transport layer.

A third aspect of the present application further provides a photovoltaic module, comprising a perovskite solar cell according to any embodiment of the first aspect of the present application, or a perovskite solar cell prepared by the method according to the second aspect of the present application. The perovskite solar cell can be used as a power supply for the photovoltaic module, or can also be used as an energy storage unit for the photovoltaic module.

EXAMPLES

The present application will be described in more detail by the following examples, which are used only for explanatory illustration, since various modifications and changes within the scope of the present application are obvious to those skilled in the art. Unless otherwise noted, all parts, percentages and ratios reported in the following examples are on a weight basis, and all reagents used in the examples are commercially available or are synthesized according to conventional methods, and can be used directly without further treatment, and the instruments used in the examples are commercially available.

Preparation of FTO Conductive Glass Electrode

A set of FTO conductive glasses with a size of 2.0 cm×2.0 cm were used, with the surface thereof being washed twice with acetone and isopropanol sequentially, and were immersed in deionized water for an ultrasonic treatment for 10 min, then dried in a blast drying oven and placed in a glove box (under N2 atmosphere).

Preparation of Electron Transport Layer Comprising a First Sub-Layer and a Second Sub-Layer.

Preparation of Second Sub-Layer

A second doping material was added to a second host material to form a second mixture.

The second mixture was spin-coated onto the FTO conductive glass electrode at a speed of 4000 rpm-6500 rpm and was heated at a constant temperature on a constant-temperature heating platform, with the coating thickness being 10-30 nm.

Preparation of First Sub-Layer

A first doping material was added to a first host material to form a first mixture.

The first mixture was spin-coated onto the second sub-layer at a speed of 4000 rpm-6500 rpm and was heated at a constant temperature on a constant-temperature heating platform, with the coating thickness being 10-30 nm.

Preparation of Perovskite Layer

The resulting first sub-layer was spin-coated with a 1.5 mol/L M solution at a speed of 3000 rpm-4500 rpm, and then the resulting product was transferred onto a constant-temperature heating platform, heated at 100° C. for 30 min and cooled to room temperature, so as to form a perovskite layer with a thickness of 500 nm.

Preparation of Hole Transport Layer

The perovskite layer was further spin-coated with a 0.1 mol/L solution of copper oxide in ethyl acetate at a speed of 4500 rpm-6000 rpm and was heated at 100° C. for 60 min, with the thickness being 30-60 nm.

Preparation of Ag Electrode

The above-mentioned sample was put into a vacuum coating machine, and an Ag electrode was evaporated onto the surface of the resulting hole transport layer under a vacuum condition of 5×10−4Pa, with the thickness of the Ag electrode being 80 nm.

The types of relevant substances in examples 1 to 21 were shown in Table 1:

Preparation of FTO Conductive Glass Electrode

A set of FTO conductive glasses with a size of 2.0 cm×2.0 cm were used, with the surface thereof being washed twice with acetone and isopropanol sequentially, and were immersed in deionized water for an ultrasonic treatment for 10 min, then dried in a blast drying oven and placed in a glove box (under N2atmosphere).

Preparation of Electron Transport Layer Comprising a First Sub-Layer, a Second Sub-Layer and a Third Sub-Layer

Preparation of Third Sub-Layer

A third doping material was doped into a third host material to form a third mixture.

The third mixture (target) was deposited onto the FTO conductive glass electrode by means of magnetron sputtering, with a sputtering power of 1000 W, an argon/oxygen ratio of 1:1, a pressure of 0.25 Pa and a sputtering thickness of 10-30 nm, followed by heating at 150° C. for 20 min.

Preparation of Second Sub-Layer

A second doping material was added to a second host material to form a second mixture.

The second mixture was spin-coated onto the FTO conductive glass electrode at a speed of 4000 rpm-6500 rpm and was heated at a constant temperature on a constant-temperature heating platform, with the coating thickness being 10-30 nm.

Preparation of First Sub-Layer

A first doping material was added to a first host material to form a first mixture.

The first mixture was spin-coated onto the second sub-layer at a speed of 4000 rpm-6500 rpm and was heated at a constant temperature on a constant-temperature heating platform, with the coating thickness being 10-30 nm.

Preparation of Perovskite Layer

The resulting electron transport layer was spin-coated with a 1.5 mol/L solution of FA0.9MA0.1PbI3in DMF at a speed of 3000 rpm-4500 rpm, then transferred onto a constant-temperature heating platform, heated at 100° C. for 30 min and cooled to room temperature to form a perovskite layer with a thickness of 500 nm.

Preparation of Hole Transport Layer

The perovskite layer was further spin-coated with a 0.1 mol/L solution of copper oxide in ethyl acetate at a speed of 4500 rpm-6000 rpm and was heated at 100° C. for 60 min, with the thickness being 30-60 nm.

Preparation of Ag Electrode

The above-mentioned sample was put into a vacuum coating machine, and an Ag electrode was evaporated onto the surface of the resulting hole transport layer under a vacuum condition of 5×10−4Pa, with the thickness of the Ag electrode being 80 nm.

The types of relevant substances in examples 22 to 40 were shown in Table 2:

Comparative Examples 1-7

Preparation of FTO Conductive Glass Electrode

A set of FTO conductive glasses with a size of 2.0 cm×2.0 cm were used, with the surface thereof being washed twice with acetone and isopropanol sequentially, and were immersed in deionized water for an ultrasonic treatment for 10 min, then dried in a blast drying oven and placed in a glove box (under N2atmosphere).

Preparation of Electron Transport Layer Comprising a First Sub-Layer and a Second Sub-Layer

Preparation of Second Sub-Layer

The FTO conductive glass electrode was spin-coated with an F solution at a speed of 4000 rpm-6500 rpm and was heated at 100° C. for 10 min, with the thickness being 10-30 nm. The specific types of the F solution were as shown in Table 3.

Preparation of First Sub-Layer

The second sub-layer was spin-coated with a 3 wt. % aqueous solution of SnO2nano-colloid at a speed of 4000 rpm-6500 rpm and then was heated on a constant-temperature heating platform at 150° C. for 15 min, with the thickness being 30-60 nm.

Preparation of Perovskite Layer

The first sub-layer was spin-coated with a 1.5 mol/L M solution at a speed of 3000 rpm-4500 rpm, then transferred onto a constant-temperature heating platform, heated at 100° C. for 30 min and then cooled to room temperature, so as to form a perovskite layer with a thickness of 500 nm. The specific types of the M solution were as shown in Table 3.

Preparation of Hole Transport Layer

The perovskite layer was spin-coated with a 0.1 mol/L S solution at a speed of 4500 rpm-6000 rpm and was heated at 100° C. for 60 min, with the thickness being 30-60 nm. The specific types of the S solution were as shown in Table 3.

Preparation of Ag Electrode

The above-mentioned sample was put into a vacuum coating machine, and an Ag electrode was evaporated onto the surface of the resulting hole transport layer under a vacuum condition of 5×10−4Pa, with the thickness of the Ag electrode being 80 nm.

Methods for Testing Performance of Perovskite Solar Cell

1. Method for Testing Energy Band Distribution

The energy band distribution of the resulting sub-layers of the electron transport layer, the hole transport layer, and the perovskite absorption layer was measured using ultraviolet photoelectron spectrometer (UPS) and X-ray photoelectron spectrometer (XPS). The test was performed at a normal temperature and pressure in an atmospheric environment, and a He-I lamp (21.2 eV) was used as the laser source. As an example, the UPS and XPS model was Escalab 250Xi (Thermo Scientific).

2. Method for Testing Power Conversion Efficiency

The energy conversion efficiency was obtained by a voltage-current characteristic test, and the test was performed at a normal temperature and pressure in an atmospheric environment, with a simulated solar light source having an intensity as standard AM1.5G. As an example, the test equipment model was IVS-KA5000 from EnliTech.

Results of Performance Test of Perovskite Solar Cell

It should be noted that in the following description, CBM represents the conduction band bottom energy level, VBM represents the valence band top energy level, and FLP represents the Fermi-level pinning, and specifically, CBM1 represents the conduction band bottom energy level of the first sub-layer, CBM2 represents the conduction band bottom energy level of the second sub-layer, CBM3 represents the conduction band bottom energy level of the third sub-layer, CBM4 represents the conduction band bottom energy level of the hole transport layer, and CBM5 represents the conduction band bottom energy level of the perovskite layer.

1. The results of performance test of examples 1 to 8 and comparative examples 1 to 4 were as shown in Table 4.

As can be seen from Table 4, for the perovskite solar cells in examples 1 to 8, when compared to comparative examples 1 to 4, the conduction band bottom energy level of each sub-layer was lower than that of the hole transport layer and the first sub-layer had a higher electron transport efficiency, and the valence band top energy levels of each sub-layer was lower than that of the hole transport layer and the electron transport layer had a higher electron transport efficiency, which was conducive to improving the power conversion efficiency of the perovskite solar cells.

2. The results of performance test of examples 9 to 14 and comparative examples 5 to 7 were as shown in Tables 5 and 6.

As can be seen from Tables 5 and 6, for the perovskite solar cells in examples 9 to 14, when compared to comparative examples 5 to 7, the difference between the conduction band bottom energy levels of the first sub-layer and the perovskite layer was −1.0 eV-1.0 eV, and particularly when the difference between the conduction band bottom energy levels of the first sub-layer and the perovskite layer was-0.3 eV-0.3 eV, the first sub-layer had a higher electron transport efficiency, which was conducive to improving the power conversion efficiency of the perovskite solar cells.

For the perovskite solar cells in examples 9 to 14, when compared to comparative examples 5 and 6, the valence band top energy level of the first sub-layer was lower than that of the perovskite layer, and the electron transport efficiency of the first sub-layer could be further improved, which was conducive to further improving the power conversion efficiency of the perovskite solar cells.

3. The results of performance test of examples 11 and 13 to 21 were as shown in Tables 7 and 8.

As can be seen from Tables 7 and 8, for the perovskite solar cells in examples 11 and 13 to 18, when compared to example 19, the difference between the Fermi levels of the first sub-layer and the perovskite layer FLP1−FLP5≤1.5 eV, and the first sub-layer had a higher electron transport efficiency, which was conducive to improving the power conversion efficiency of the perovskite solar cells.

For the perovskite solar cells in examples 11 and 13 to 18, when compared to example 20, the difference between the conduction band bottom energy level and the Fermi level of the first sub-layer CBM1−FLP1≤1.5 eV, which showed a higher power conversion efficiency.

For the perovskite solar cells in examples 13 to 18, when compared to example 21, the difference between the conduction band bottom energy level and the valence band top energy level of the first sub-layer CBM−VBM≥1.5 eV, which showed a higher power conversion efficiency.

4. The results of performance test of examples 22 to 40 were as shown in Table 9.

As can be seen from Table 9, when compared to example 1, the electron transport layer of the perovskite solar cells in examples 22 to 40 had three sub-layers, which was conducive to improving the power conversion efficiency of the perovskite solar cells.

While the present application has been described with reference to some embodiments, various modifications may be made thereto and equivalents may be substituted for components thereof without departing from the scope of the present application, in particular, as long as there are no structural conflicts, the technical features mentioned in embodiments can be combined in any manner. The present application is not limited to the specific embodiments disclosed herein but includes all the technical solutions that fall within the scope of the claims.