Solar Cells

Abstract

The solar cell 100 of the present disclosure comprises a first electrode 2, a second electrode 6, a photoelectric conversion layer 4 disposed between the first electrode 2 and the second electrode 6, and an electron transport layer 3 disposed between the first electrode 2 and the photoelectric conversion layer 4. At least one electrode selected from the first electrode 2 and the second electrode 6 has light transparency. The photoelectric conversion layer 4 contains a perovskite compound composed of monovalent cations, divalent cations and halogen anions. The electron transport layer 3 contains a metal oxynitride having electron conductivity.

Description

Technical Field

[0001] The present disclosure relates to solar cells. Background Art

[0002] In recent years, perovskite solar cells have been studied and developed. In perovskite solar cells, a perovskite compound represented by the chemical formula ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a halogen anion) is used as a photoelectric conversion material.

[0003] Non-patent document 1 and patent document 1 disclose the use of a perovskite compound represented by the chemical formula CH3NH3SnI3 (hereinafter referred to as "MASnI3") as a photoelectric conversion material for a perovskite solar cell. Non-patent document 1 and patent document 1 also disclose a perovskite compound represented by the chemical formula (NH2)2CHSnI3 (hereinafter referred to as "FASnI3"). In addition, patent document 1 also discloses a perovskite compound represented by the chemical formula CH3NH3PbI3 (hereinafter referred to as "MAPbI3") and the chemical formula (NH2)2CHPbI3 (hereinafter referred to as "FAPbI3") in which the divalent cation is Pb as a photoelectric conversion material.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-17252

[0007] Non-patent literature

[0008] Non-patent literature 1: Shuyan Shao et.Al. "Highly Reproducible Sn-Based HybridPerovskite Solar Cells with 9% Efficiency", Advanced Energy Materials, 2018, Vol. 8, 1702019

[0009] Non-patent document 2: Atsushi Kogo et al., "Nb2O5 Blocking Layer for High Open-circuit Voltage Perovskite Solar Cells", Chem. Lett., 2015, Vol. 44, 829-830 Summary of the invention

[0010] Technical problem to be solved by the invention

[0011] An object of the present disclosure is to provide a perovskite solar cell having high photoelectric conversion efficiency.

[0012] Means for solving technical problems

[0013] The solar cell disclosed in the present invention comprises a first electrode, a second electrode, a photoelectric conversion layer arranged between the first electrode and the second electrode, and an electron transport layer arranged between the first electrode and the photoelectric conversion layer. Here, at least one electrode selected from the first electrode and the second electrode is light-transmitting, the photoelectric conversion layer contains a perovskite compound composed of monovalent cations, divalent cations and halogen anions, and the electron transport layer contains a metal oxynitride with electron conductivity.

[0014] Effects of the Invention

[0015] The present disclosure provides a perovskite solar cell with high photoelectric conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The electron density of the electron transport layer is 1×10 8 cm -3 , 1×10 10 cm -3 , 1×10 12 cm -3 , 1×10 14 cm -3 , 1×10 16 cm -3 , 1×10 18 cm -3 and 1×10 20 cm -3 The simulation results of .

[0017] Figure 2 A cross-sectional view showing a solar cell according to an embodiment of the present disclosure.

[0018] Figure 3 A cross-sectional view showing a solar cell according to a modified example of the embodiment of the present disclosure. DETAILED DESCRIPTION

[0019] <Definition of Terms>

[0020] The term "perovskite compound" used in this specification refers to a perovskite crystal structure represented by a chemical formula ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a halogen anion) and a structure having a crystal similar thereto.

[0021] The term "perovskite solar cell" used in this specification refers to a solar cell including a perovskite compound as a photoelectric conversion material.

[0022] The term "tin-based perovskite compound" used in this specification refers to a perovskite compound containing tin.

[0023] <Knowledge that forms the basis of this disclosure>

[0024] The knowledge that forms the basis of the present disclosure is as follows.

[0025] Perovskite compounds have a band gap of about 1.1 to 1.6 eV. Therefore, perovskite compounds are suitable as photoelectric conversion materials for solar cells. Perovskite solar cells have reported high photoelectric conversion efficiency, and further improvement of the photoelectric conversion efficiency is required.

[0026] In order to improve the photoelectric conversion efficiency, it is necessary to increase the electron density of the electron transport layer more than the current situation. Figure 1 This is a graph showing the relationship between the voltage of the solar cell (horizontal axis) and the current density of the solar cell (vertical axis) in the electron density of each electron transport layer. This graph is the result of calculation using device simulation (software name: SCAPS). Figure 1 The electron density of the electron transport layer is 1×10 8 cm -3 , 1×10 10 cm -3 , 1×10 12 cm -3 , 1×10 14 cm -3 , 1×10 16 cm -3 , 1×10 18 cm -3 and 1×10 20 cm -3 The simulation results are given by Figure 1 It can be seen that by increasing the electron density of the electron transport layer, the open circuit voltage increases. The higher the electron density of the electron transport layer, the greater the built-in potential applied to the perovskite layer and the greater the open circuit voltage. For this reason, by increasing the electron density of the electron transport layer, the increase in the open circuit voltage and photoelectric conversion efficiency of the perovskite solar cell can be preferred. In order to obtain high efficiency (for example, 27mA / cm at a voltage of 0.8 volts) 2 It is necessary to make the electron density of the electron transport layer 1×10 16 cm -3 The electron density of the electron transport layer formed by oxide-based electron transport materials such as TiO2 and Nb2O5 reported in the past is 1×10 15 cm -3 Therefore, new electron transport materials with high electron density become necessary.

[0027] Oxynitrides have a higher electron density than oxides that have been used as electron transport materials in the past. Generally speaking, the oxygen sites of oxides that become n-type semiconductors become vacancies, and these defects become donors, thereby exhibiting electron transport properties. On the other hand, nitrogen sites in oxynitrides are easily converted into vacancies in the atmosphere, and nitrogen sites are easily replaced by oxygen ions. These two donor defects in oxynitrides are easier to generate than oxygen vacancies in oxides, and since they provide more electrons, the electron density of oxynitrides is higher than that of oxides.

[0028] Based on these findings, the present inventors provide a solar cell containing a perovskite compound and having an electron transport layer with a high electron density.

[0029] <Embodiments of the present disclosure>

[0030] Below, while referring to the attached Figure 1 The embodiments of the present disclosure will be described in detail.

[0031] Figure 2 1 is a cross-sectional view of a solar cell 100 according to this embodiment. Figure 2 As shown, the solar cell 100 of this embodiment includes a first electrode 2 , a second electrode 6 , a photoelectric conversion layer 4 provided between the first electrode 2 and the second electrode 6 , and an electron transport layer 3 provided between the first electrode 2 and the photoelectric conversion layer 4 .

[0032] The first electrode 2 faces the second electrode 6 in such a manner that the electron transport layer 3 and the photoelectric conversion layer 4 are located between the first electrode 2 and the second electrode 6. At least one electrode selected from the first electrode 2 and the second electrode 6 has light transparency. In this specification, the wording "the electrode has light transparency" means that at any wavelength of light having a wavelength of 200 to 2000 nanometers, 10% or more of the light is transmitted through the electrode.

[0033] (Photoelectric conversion layer 4)

[0034] The photoelectric conversion layer 4 contains a perovskite compound composed of monovalent cations, divalent cations, and halogen anions as a photoelectric conversion material. The photoelectric conversion material is a light absorbing material.

[0035] In the present embodiment, the perovskite compound may be a compound represented by a chemical formula ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a halogen anion).

[0036] According to the conventional representation of perovskite compounds, A, B and X are also referred to as A site, B site and X site, respectively, in this specification.

[0037] In this embodiment, the perovskite compound may have a perovskite type crystal structure represented by the chemical formula ABX3. As an example, a monovalent cation is located at the A site, a divalent cation is located at the B site, and a halogen anion is located at the X site.

[0038] The A site, B site and X site can also be occupied by multiple types of ions.

[0039] (A site)

[0040] The monovalent cation at the A site is not limited. Examples of the monovalent cation A are organic cations or alkali metal cations. Examples of organic cations are methylammonium cations (i.e., CH3NH3 + ), carbamidinium cation (i.e. NH2CHNH2 + ), phenylethylammonium cation (i.e. C6H5C2H4NH3 + ), or a guanidinium cation (i.e. CH6N3 + An example of an alkali metal cation is a cesium cation (i.e., Cs + ).

[0041] For high photoelectric conversion efficiency, the monovalent cation A preferably contains a formamidinium cation.

[0042] The monovalent cation located at the A site may be composed of two or more types of cations.

[0043] The A site may mainly contain formamidinium cations. The phrase "the A site mainly contains formamidinium cations" means that the molar amount of formamidinium cations is the highest relative to the total molar amount of monovalent cations.

[0044] The A site may be substantially composed of formamidinium cations. The phrase "A site is substantially composed of formamidinium cations" means that the molar ratio of the molar number of formamidinium cations to the total molar number of monovalent cations is 90% or more, preferably 95% or more.

[0045] (Site B)

[0046] The divalent cation at the B site is not limited. Examples of the divalent cation A are metal cations. Examples of metal cations are lead ions (Pb 2+ ), tin ions (Sn 2+ ), Germanium ions (Ge 2+ ), zinc ion (Zn 2+ ), cadmium ions (Cd 2+ ), beryllium ion (Be 2+ ), magnesium ion (Mg 2+ ), calcium ions (Ca 2+ ), strontium ion (Sr 2+ ), barium ions (Ba 2+), titanium ions (Ti 2+ ), vanadium ions (V 2 + ), chromium ion (Cr 2+ ), manganese ion (Mn 2+ ), iron ions (Fe 2+ ), cobalt ions (Co 2+ ), nickel ions (Ni 2+ ), copper ions (Cu 2+ ), palladium ions (Pd 2+ ), platinum ions (Pt 2+ ), Neodymium (Nd 2+ ), samarium ion (Sm 2+ ), europium ions (Er 2+ ), Dysprosium ion (Dy 2+ ), thulium ion (Tm 2+ ), Ytterbium ions (Yb 2+ ), or neptunium ions (NP 2+ ).

[0047] For high photoelectric conversion efficiency, it is preferred that the divalent cations include tin ions (Sn 2+ ) and lead ions (Pb 2+ )

[0048] The divalent cation located at the B site may be composed of two or more types of cations.

[0049] The divalent cation located at the B site is composed of two or more metal cations other than divalent cations, and can be treated as a divalent cation on average. For example, when a monovalent cation and a trivalent cation occupy the B site with the same probability, when the whole system is averaged, the divalent cation is located at the B site. An example of such a monovalent cation is a lithium ion (Li + ), sodium ion (Na + ), potassium ion (K + ), rubidium ions (Rb + ), cesium ion (Cs + ), copper ions (Cu + ), silver ions (Ag + ), gold ions (Au + ), mercury ion (Hg + ), indium ions (In + ) or thallium ion (Tl + An example of a trivalent cation is scandium (Sc 3+ ), yttrium ion (Y 3+ ), lanthanum ions (La 3+ ), cerium ion (Ce 3+ ), praseodymium ion (Pr 3+ ), neodymium ions (Nd3+ ), promethium ion (Pm 3+ ), samarium ion (Sm 3+ ), europium ions (Er 3+ ), gadolinium ions (Gd 3+ ), terbium ions (Tb 3+ ), Dy 3+ ), holmium ion (Ho 3+ ), erbium ions (Er 3+ ), thulium ion (Tm 3+ ), Ytterbium ions (Yb 3+ ), Lutetium ion (Lu 3+ ), titanium ions (Ti 3+ ), vanadium ions (V 3+ ), chromium ion (Cr 3+ ), manganese ion (Mn 3+ ), boron ion (B 3 + ), aluminum ions (Al 3+ ), manganese ion (Mn 3+ ), iron ions (Fe 3+ ), cobalt ions (Co 3+ ), nickel ions (Ni 3+ ), copper ions (Cu 3+ ), niobium ions (Nb 3+ ), molybdenum ion (Mo 3+ ), ruthenium ions (Ru 3+ ), rhodium ions (Rh 3+ ), palladium ions (Pd 3+ ), silver ions (Ag 3+ ), titanium ions (Ta 3+ ), iridium ion (Ir 3+ ), gold ions (Au 3+ ), gallium ions (Ga 3+ ), indium ions (In 3+ ), thallium ion (Tl 3+ ), phosphorus ion (P 3+ ), arsenic ions (As 3+ ), antimony ions (Sb 3+ ) or bismuth ion (Bi 3+ ).

[0050] (X site)

[0051] For high photoelectric conversion efficiency, the halogen anion located at the X site preferably includes an iodide ion. The halogen anion located at the X site may be composed of two or more halogen ions.

[0052] The X site may mainly contain iodide ions. The words "the X site mainly contains iodide ions" mean that the ratio of the molar amount of iodide ions to the total molar amount of halogen anions is the highest. The X site may also be substantially composed of iodide ions. "The X site substantially consists of iodide ions" means that the molar ratio of the molar number of iodide ions to the total molar number of halogen anions is 90% or more, preferably 95% or more.

[0053] The photoelectric conversion layer 4 may further include materials other than the photoelectric conversion material. For example, the photoelectric conversion layer 4 may further include a quenching substance for reducing the defect density of the perovskite compound. The quenching substance is a fluorine compound such as tin fluoride. The molar ratio of the quenching substance to the photoelectric conversion material may be 5% to 20%.

[0054] The photoelectric conversion layer 4 may mainly contain a perovskite compound composed of monovalent cations, divalent cations, and halogen anions.

[0055] The words “the photoelectric conversion layer 4 mainly contains a perovskite compound composed of monovalent cations, divalent cations and halogen anions” means that the photoelectric conversion layer 4 contains 70 mass % or more (preferably 80 mass % or more) of a perovskite compound composed of monovalent cations, divalent cations and halogen anions.

[0056] Photoelectric conversion layer 4 may contain impurities. Photoelectric conversion layer 4 may further contain a compound other than the above-mentioned perovskite compound.

[0057] The photoelectric conversion layer 4 may have a thickness of 100 nanometers to 10 micrometers or less, and preferably has a thickness of 100 nanometers to 1000 nanometers or less. The thickness of the photoelectric conversion layer 4 depends on the magnitude of its light absorption.

[0058] The photoelectric conversion layer 4 can be formed by a coating method using a solution or the like.

[0059] (Electron transport layer 3)

[0060] The electron transport layer 3 contains a metal oxynitride having electron conductivity as an electron transport material. The electron density of the metal oxynitride is higher than that of the metal oxide. Therefore, when the metal oxynitride having electron conductivity and the metal oxide having electron conductivity are compared with each other, the metal oxynitride is more excellent in terms of electron transport. In addition, here, the metal oxynitride having electron conductivity refers to a 1×10 -7 S cm -1 The metal oxynitride contained in the electron transport layer 3 preferably has an electrical conductivity of 1×10 -6 S cm -1 More preferably, the conductivity is 1×10 -5S cm -1 For example, the conductivity of TiO2, SnO2 and Nb2O5 reported as electron transport materials is 0.01S·cm -1 , 0.01S·cm -1 and 1×10 -5 S cm -1 On the other hand, the conductivity of Ta2O5, which has not been reported as an electron transport material, is 1×10 -8 S cm -1 .

[0061] As demonstrated in Comparative Examples 3 and 4 described later, a solar cell having an electron transport layer 3 formed of a metal oxynitride (e.g., titanium oxynitride in Comparative Example 4) produced by adding nitrogen to a metal oxide lacking electron conductivity (e.g., titanium oxide in Comparative Example 3) has a significantly low photoelectric conversion efficiency (e.g., 0%). In other words, by adding nitrogen to a metal oxide lacking electron conductivity (e.g., titanium oxide with an electrical conductivity of 1×10 -8 S cm -1 Metal oxynitrides obtained by adding nitrogen to metal oxides (hereinafter referred to as metal oxides) lack electron conductivity like metal oxides, so a solar cell having an electron transport layer formed of such metal oxynitrides will not function as a solar cell.

[0062] Metal oxynitride is produced by adding nitrogen to a metal oxide having electron conductivity. The metal oxynitride produced in this way has a high electron density. A perovskite solar cell having an electron transport layer 3 containing an oxynitride having a high electron density can expect a high open circuit voltage and a high photoelectric conversion efficiency. That is, the solar cell of this embodiment can achieve a high photoelectric conversion efficiency.

[0063] Examples of metal oxides having electron conductivity are Nb2O5, SnO2, TiO2, ZnO, In2O3, WO3, Fe2O3, CeO2, SrTiO3, Zn2SnO4, or BaSnO3. Therefore, in the solar cell of this embodiment, examples of metal oxynitrides contained in the electron transport layer 3 as electron transport materials are (i) niobium oxynitride produced by adding nitrogen to Nb2O5;

[0064] (ii) Tin oxynitride produced by adding nitrogen to SnO2

[0065] (iii) titanium oxynitride produced by adding nitrogen to TiO2,

[0066] (iv) Zinc oxynitride produced by adding nitrogen to ZnO,

[0067] (v) Indium oxynitride produced by adding nitrogen to In2O3,

[0068] (vi) Tungsten oxynitride produced by adding nitrogen to WO3,

[0069] (vii) Iron oxynitride produced by adding nitrogen to Fe2O3,

[0070] (viii) Cesium oxynitride produced by adding nitrogen to CeO2,

[0071] (iX) Strontium titanate nitride produced by adding nitrogen to SrTiO3,

[0072] (X) Tin zinc nitride prepared by adding nitrogen to Zn2SnO4, or (Xi) Tin barium nitride prepared by adding nitrogen to BaSnO3. That is, the metal oxynitride contained in the electron transport layer can be at least one selected from niobium oxynitride, tin oxynitride, titanium oxynitride, zinc oxynitride, indium oxynitride, tungsten oxynitride, iron oxynitride, cesium oxynitride, strontium titanate nitride, tin zinc nitride and barium tin nitride. For higher photoelectric conversion efficiency, the metal oxynitride contained in the electron transport layer can be at least one selected from niobium oxynitride and tin oxynitride.

[0073] Perovskite oxide ABO3 also has electron conductivity. Examples of perovskite oxides with electron conductivity are

[0074] (i) an oxide in which a divalent cation is located at the A site and a tetravalent cation is located at the B site;

[0075] (ii) an oxide in which a trivalent cation is located at the A site and a trivalent cation is located at the B site;

[0076] or (iii) an oxide in which a tetravalent cation is located at the A site and a divalent cation is located at the B site.

[0077] An example of a perovskite type oxide is SrTiO3.

[0078] The spinel oxide A2BO4 also has electron conductivity and electron transport properties. Examples of spinel oxides with electron conductivity are

[0079] (i) an oxide in which a divalent cation is located at the A site and a tetravalent cation is located at the B site;

[0080] or (ii) an oxide in which a trivalent cation is located at the A site and a divalent cation is located at the B site.

[0081] An example of a spinel type oxide is Zn2SnO4.

[0082] Here, in the above-mentioned perovskite-type oxide and spinel-type oxide, the divalent cation is lead ion (Pb 2+ ), tin ions (Sn 2+ ), Germanium ions (Ge 2+ ), zinc ion (Zn 2+ ), cadmium ions (Cd 2+ ), beryllium ion (Be 2+ ), magnesium ion (Mg 2+ ), calcium ions (Ca 2+ ), strontium ion (Sr 2+ ), barium ions (Ba 2+ ), titanium ions (Ti 2+ ), vanadium ions (V 2+ ), chromium ion (Cr 2+ ), manganese ion (Mn 2 + ), iron ions (Fe 2+ ), cobalt ions (Co 2+ ), nickel ions (Ni 2+ ), copper ions (Cu 2+ ), palladium ions (Pd 2+ ), platinum ions (Pt 2+ ), Neodymium (Nd 2+ ), samarium ion (Sm 2+ ), europium ions (Er 2+ ), Dysprosium ion (Dy 2+ ), thulium ion (Tm 2+ ), Ytterbium ions (Yb 2+ ) or neptunium ion (NP 2+ ).

[0083] In the above perovskite-type oxides and spinel-type oxides, the trivalent cation is a scandium ion (Sc 3+ ), yttrium ion (Y 3 + ), lanthanum ions (La 3+ ), cerium ion (Ce 3+ ), praseodymium ion (Pr 3+ ), neodymium ions (Nd 3+ ), promethium ion (Pm 3+ ), samarium ion (Sm 3+ ), europium ions (Er 3+ ), gadolinium ions (Gd 3+ ), terbium ions (Tb 3+ ), Dy 3+ ), holmium ion (Ho 3+ ), erbium ions (Er 3+ ), thulium ion (Tm 3+ ), Ytterbium ions (Yb 3+), Lutetium ion (Lu 3+ ), titanium ions (Ti 3+ ), vanadium (V 3+ ), chromium ion (Cr 3+ ), manganese ion (Mn 3+ ), boron ion (B 3+ ), aluminum ions (Al 3+ ), manganese ion (Mn 3+ ), iron ions (Fe 3+ ), cobalt ions (Co 3+ ), nickel ions (Ni 3+ ), copper ions (Cu 3+ ), niobium ions (Nb 3+ ), molybdenum ion (Mo 3+ ), ruthenium ions (Ru 3+ ), rhodium ions (Rh 3+ ), palladium ions (Pd 3+ ), silver ions (Ag 3+ ), titanium ions (Ta 3+ ), iridium ion (Ir 3+ ), gold ions (Au 3+ ) Gallium ion (Ga 3+ ), indium ions (In 3+ ), thallium ion (Tl 3 + ), phosphorus ion (P 3+ ), arsenic ions (As 3+ ), antimony ions (Sb 3+ ) or bismuth ion (Bi 3+ ).

[0084] In the above perovskite-type oxides and spinel-type oxides, the tetravalent cation is a carbon ion (C 4+ ), silicon ions (Si 4 + ), sulfide ion (S 4+ ), titanium ions (Ti 4+ ), vanadium ions (V 4+ ), chromium ion (Cr 4+ ), manganese ion (Mn 4+ ), iron ions (Fe 4+ ), cobalt ions (Co 4+ ), nickel ions (Ni 4+ ), Germanium ions (Ge 4+ ), selenium ion (Se 4+ ), zirconium ion (Zr 4+ ), niobium ions (Nb 4+ ), molybdenum ion (Mo 4+ ), technetium ion (Tc 4+ ), ruthenium ions (Ru4+ ), rhodium ions (Rh 4+ ), palladium ions (Pd 4+ ), tin ions (Sn 4+ ), tellurium ion (Te 4+ ), hafnium ions (Hf 4+ ), titanium ions (Ta 4+ ), tungsten ion (W 4+ ), rhenium ion (Re 4+ ), osmium ion (Os 4+ ), iridium ion (Ir 4 + ), platinum ions (Pt 4+ ), lead ion (Pb 4+ ), Polonium ion (Po 4+ ), cerium ion (Ce 4+ ), praseodymium ion (Pr 4+ ) or terbium ion (Tb 4 + ).

[0085] For high photoelectric conversion efficiency, the electron transport layer 3 preferably has a thickness of 2 nanometers or more. When the thickness is 2 nanometers or more, the hole density increase due to the quantum effect can be suppressed, so the hole blocking function is not lost, and the photoelectric conversion efficiency is improved.

[0086] From the viewpoint of low resistance of the electron transport layer 3 , in order to improve the photoelectric conversion efficiency of the solar cell, the electron transport layer 3 preferably has a thickness of 500 nanometers or less.

[0087] The electron density of the electron transport layer 3 comprising metal oxynitride may be 10 16 cm -3 ~10 20 cm -3 The electron density of the electron transport layer 3 is 10 20 cm -3 When the electron density of the electron transport layer 3 is less than 10, the interface recombination between the excess electrons in the electron transport layer 3 and the holes in the photoelectric conversion layer can be suppressed. Therefore, the photoelectric conversion efficiency is improved. 16 cm -3 In the above case, since the electron transport property of the electron transport layer 3 is improved, the photoelectric conversion efficiency is improved.

[0088] When the electron transport layer 3 contains niobium oxynitride, the ratio N / O of the amount of N to the amount of O in the niobium oxynitride contained in the electron transport layer 3 may be greater than 0 and less than 1, or may be 0.05 to 0.28. The value of the ratio N / O may be measured by X-ray photoelectron spectroscopy (hereinafter referred to as "XPS method"), energy dispersive X-ray analysis (hereinafter referred to as "EDX method"), inductively coupled plasma optical emission spectrometry (hereinafter referred to as "ICP-OES method"), or Rutherford backscattering analysis (hereinafter referred to as "RBS method").

[0089] When the electron transport layer 3 contains tin oxynitride, the N / O ratio of the amount of N to the amount of O in the tin oxynitride contained in the electron transport layer 3 may be greater than 0 and less than 0.66, or may be 0.05 to 0.15. The value of the N / O ratio can be measured by XPS, EDX, ICP-OES or RBS.

[0090] The electron transport layer 3 may mainly contain a metal oxynitride having electron conductivity. The electron transport layer 3 may be substantially composed of only a metal oxynitride having electron conductivity. The electron transport layer 3 may be substantially composed of only a metal oxynitride having electron conductivity.

[0091] The phrase “the electron transport layer 3 mainly contains a metal oxynitride having electron conductivity” means that the electron transport layer 3 contains 50 mol % or more (preferably 60 mol % or more) of the metal oxynitride having electron conductivity.

[0092] The phrase “the electron transport layer 3 is substantially composed of only the metal oxynitride having electron conductivity” means that the electron transport layer 3 contains 90 mol % or more (preferably 95 mol % or more) of the metal oxynitride having electron conductivity.

[0093] The electron transport layer 3 may contain a compound other than metal oxynitride as an electron transport material. The electron transport material other than metal oxynitride may be a material known as an electron transport material for solar cells. Hereinafter, for the purpose of distinction, the metal oxynitride is referred to as the first electron transport material, and the electron transport material other than metal oxynitride is referred to as the second electron transport material.

[0094] Next, the second electron transport material will be described.

[0095] The second electron transport material may be a semiconductor having a band gap of 3.0 eV or more. When the electron transport layer 3 contains a semiconductor having a band gap of 3.0 eV or more, visible light and infrared light pass through the electron transport layer 3 to reach the photoelectric conversion layer 4. Examples of semiconductors having a band gap of 3.0 eV or more are organic or inorganic n-type semiconductors.

[0096] Examples of the organic n-type semiconductor are imide compounds, quinone compounds, fullerenes, or fullerene derivatives.

[0097] Examples of inorganic n-type semiconductors are metal oxides, metal nitrides, and perovskite oxides.

[0098] Examples of metal oxides are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si or Cr. TiO2 is preferred.

[0099] An example of a metal nitride is GaN.

[0100] Examples of perovskite type oxides are SrTiO3 or CaTiO3.

[0101] The electron transport layer 3 may be in contact with the photoelectric conversion layer 4. Alternatively, the electron transport layer 3 may not be in contact with the photoelectric conversion layer 4. When the electron transport layer 3 is in contact with the photoelectric conversion layer 4, the electron transport material including oxynitride may be provided on the surface of the electron transport layer 3 in contact with the photoelectric conversion layer 4.

[0102] The electron transport layer 3 may be composed of a plurality of layers formed of mutually different electron transport materials. When the electron transport layer 3 is composed of a plurality of layers, the layer in contact with the photoelectric conversion layer 4 may contain a metal oxynitride having electron conductivity.

[0103] like Figure 2 As shown, in the solar cell 100, the first electrode 2, the electron transport layer 3, the photoelectric conversion layer 4, the hole transport layer 5 and the second electrode 6 are sequentially stacked on the substrate 1. That is, the hole transport layer 5 is provided between the second electrode 6 and the photoelectric conversion layer 4. The solar cell 100 may not have the substrate 1. The solar cell 100 may not have the hole transport layer 5.

[0104] Hereinafter, each component of the solar cell 100 will be described in detail.

[0105] (Substrate 1)

[0106] The substrate 1 holds the first electrode 2, the photoelectric conversion layer 4, and the second electrode 6. The substrate 1 can be formed of a transparent material. An example of the substrate 1 is a glass substrate or a plastic substrate. An example of a plastic substrate is a plastic film. When the first electrode 2 has sufficient strength, the first electrode 2 holds the photoelectric conversion layer 4 and the second electrode 6, so the solar cell 100 may not have the substrate 1.

[0107] (First electrode 2 and second electrode 6)

[0108] The first electrode 2 and the second electrode 6 are conductive. At least one of the first electrode 2 and the second electrode 6 is light-transmissive. Light in the visible region to the near-infrared region can pass through the light-transmissive electrode. The light-transmissive electrode can be formed of a transparent and conductive material.

[0109] Examples of such materials are

[0110] (i) titanium oxide doped with at least one selected from lithium, magnesium, niobium and fluorine;

[0111] (ii) gallium oxide doped with at least one selected from tin and silicon;

[0112] (iii) gallium nitride doped with at least one selected from silicon and oxygen;

[0113] (iv) indium-tin composite oxide;

[0114] (v) tin oxide doped with at least one selected from antimony and fluorine;

[0115] (vi) zinc oxide doped with at least one of boron, aluminum, gallium and indium;

[0116] or (vii) a complex thereof.

[0117] The light-transmitting electrode can be formed by using an opaque material and a pattern that allows light to pass through. Examples of patterns that allow light to pass through are linear, curved, latticed, or regularly or irregularly arranged punched metal patterns with multiple fine through holes. When the light-transmitting electrode has these patterns, light can pass through the portion where the electrode material does not exist. Examples of opaque materials are platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or an alloy containing any of them. Conductive carbon materials can also be used as opaque materials.

[0118] Since the solar cell 100 includes the electron transport layer 3 between the photoelectric conversion layer 4 and the first electrode 2, the first electrode 2 need not have a blocking property for holes from the photoelectric conversion layer 4. Therefore, the material of the first electrode 2 can be a material capable of making ohmic contact with the photoelectric conversion layer 4.

[0119] When the solar cell 100 does not have the hole transport layer 5, the second electrode 6 is formed of, for example, a material having a barrier property against electrons from the photoelectric conversion layer 4. In this case, the second electrode 6 is not in ohmic contact with the photoelectric conversion layer 4. The barrier property against electrons from the photoelectric conversion layer 4 refers to the property of allowing only holes generated in the photoelectric conversion layer 4 to pass through, but not electrons. The Fermi energy of the material having a barrier property against electrons is lower than the energy level at the lower end of the conduction band of the photoelectric conversion layer 4. The Fermi energy of the material having a barrier property against electrons may be lower than the Fermi energy level of the photoelectric conversion layer 4. Examples of materials having a barrier property against electrons are carbon materials such as platinum, gold, or graphite.

[0120] When the solar cell 100 includes the hole transport layer 5 between the photoelectric conversion layer 4 and the second electrode 6 , the second electrode 6 may not have a barrier property against electrons from the photoelectric conversion layer 4 . In this case, the second electrode 6 may be in ohmic contact with the photoelectric conversion layer 4 .

[0121] The material having a blocking property for holes from the photoelectric conversion layer 4 may not be light-transmitting. The material having a blocking property for electrons from the photoelectric conversion layer 4 may not be light-transmitting. Therefore, when the first electrode 2 or the second electrode 6 is formed using these materials, the first electrode 2 or the second electrode 6 has the above-mentioned pattern such that light passes through the first electrode 2 or the second electrode 6.

[0122] The light transmittance of each of the first electrode 2 and the second electrode 6 may be 50% or more, or 80% or more. The wavelength of light transmitted through the electrodes depends on the absorption wavelength of the photoelectric conversion layer 4. The thickness of each of the first electrode 2 and the second electrode 6 is, for example, in the range of 1 nm to 1000 nm.

[0123] (Hole Transport Layer 5)

[0124] The hole transport layer 5 is composed of an organic substance or an inorganic semiconductor. Representative examples of organic substances used as the hole transport layer 5 are 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (hereinafter referred to as "spiro-OMeTAD"), poly[bis-(4-phenyl)(2,4,6)-trimethylaniline]amine, enyl)(2,4,6-trimethylphenyl)amine]) (hereinafter referred to as "PTAA"), poly(3-hexylthiophene-2,5-diyl) (hereinafter referred to as "P3HT"), poly(3,4-ethylenedioxythiophene) (hereinafter referred to as "PEDOT") or copper phthalocyanine (hereinafter referred to as "CuPC").

[0125] Examples of inorganic semiconductors are Cu2O, CuGaO2, CuSCN, CuI, NiO X 、MoO X , V2O5 or graphite oxide and other carbon materials.

[0126] The hole transport layer 5 may include a plurality of layers formed of materials different from each other.

[0127] The thickness of the hole transport layer 5 may be 1 nm to 1000 nm, 10 nm to 500 nm, or 10 nm to 50 nm. When the thickness of the hole transport layer 5 is 1 nm to 1000 nm, sufficient hole transport properties can be exhibited. Furthermore, when the thickness of the hole transport layer 5 is 1 nm to 1000 nm, the resistance of the hole transport layer 5 is low, so light is efficiently converted into electricity.

[0128] The hole transport layer 5 may contain a supporting electrolyte and a solvent. The supporting electrolyte and the solvent stabilize the holes in the hole transport layer 5 .

[0129] Examples of supporting electrolytes are ammonium salts or alkali metal salts. Examples of ammonium salts are tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, imidazolium salts or pyridinium salts. Examples of alkali metal salts are lithium bis(trifluoromethanesulfonyl)imide (hereinafter referred to as "LiTFSI"), LiPF6, LiBF4, lithium perchlorate or potassium tetrafluoroborate.

[0130] The solvent contained in the hole transport layer 5 may also have high ion conductivity. The solvent may be an aqueous solvent or an organic solvent. From the viewpoint of stabilization of the solute, an organic solvent is preferred. Examples of organic solvents are heterocyclic compounds such as tert-butylpyridine, pyridine or n-methylpyrrolidone.

[0131] The solvent contained in the hole transport layer 5 may also be an ionic liquid. The ionic liquid may be used alone or in a mixture with other solvents. The ionic liquid is preferred in terms of low volatility and high flame retardancy.

[0132] Examples of the ionic liquid include imidazolium salt compounds such as 1-ethyl-3-methylimidazolium tetracyanoborate, pyridine compounds, alicyclic amine compounds, aliphatic amine compounds, and azoamine compounds.

[0133] (Effects of solar cells)

[0134] Next, the basic effects of the solar cell 100 are described. When light is irradiated to the solar cell 100, the photoelectric conversion layer 4 absorbs the light, and excited electrons and holes are generated inside the photoelectric conversion layer 4. The excited electrons move to the electron transport layer 3. And the holes generated in the photoelectric conversion layer 4 move to the hole transport layer 5. The electron transport layer 3 is connected to the first electrode 2, and the hole transport layer 5 is connected to the second electrode 6, so the current is taken out from the first electrode 2 functioning as a negative electrode and the second electrode 6 functioning as a positive electrode.

[0135] (Method of Manufacturing Solar Cell 100)

[0136] The solar cell 100 is produced, for example, by the following method.

[0137] First, the first electrode 2 is formed on the surface of the substrate 1 by chemical vapor deposition (hereinafter referred to as “CVD method”) or sputtering.

[0138] Next, the electron transport layer 3 is formed on the first electrode 2 by, for example, sputtering.

[0139] As a target used in the sputtering method, for example, a metal oxide having electron conductivity is used. Using a target formed of such a metal oxide and in an atmosphere containing nitrogen, a film containing metal oxynitride is formed by sputtering. The formed film containing metal oxynitride is the electron transport layer 3.

[0140] The photoelectric conversion layer 4 is formed on the electron transport layer 3. The photoelectric conversion layer 4 can be formed, for example, as follows. Hereinafter, the formation of a layer containing (HC(NH2)2) 1-y-z (C6H5CH2CH2NH3) y (CH6N3) zSnI3 (where 0 < y, 0 < z, and 0 < (y + z) < 1, hereinafter referred to as "FA 1-y-z PEA y GA z SnI3"), a method for the photo - electric conversion layer 4 of a perovskite compound.

[0141] First, add SnI2, HC(NH2)2I (hereinafter referred to as "FAI"), C6H5CH2CH2NH3I (hereinafter referred to as "PEAI"), and CH6N3I (hereinafter referred to as "GAI") to an organic solvent to obtain a mixed solution. Examples of the organic solvent are a mixture of dimethyl sulfoxide (hereinafter referred to as "DMSO") and N,N - dimethylformamide (hereinafter referred to as "DMF") (DMS:DMF = 1:1 (volume ratio)).

[0142] The molar concentration of SnI2 can be 0.8 mol / L to 2.0 mol / L, and can also be 0.8 mol / L to 1.5 mol / L.

[0143] The molar concentration of FAI can be 0.8 mol / L to 2.0 mol / L, and can also be 0.8 mol / L to 1.5 mol / L.

[0144] The molar concentration of PEAI can be 0.1 mol / L to 0.6 mol / L, and can also be 0.3 mol / L to 0.5 mol / L.

[0145] The molar concentration of GAI can be 0.1 mol / L to 0.6 mol / L, and can also be 0.3 mol / L to 0.5 mol / L.

[0146] Next, heat the mixed solution to a temperature below 40°C to 180°C. Thus, a mixed solution in which SnI2, FAI, PEAI, and GAI are dissolved is obtained. Then, leave the mixed solution at room temperature.

[0147] Next, use the spin - coating method to coat the mixed solution on the electron - transport layer 3 to form a coated film. Then, heat the coated film at a temperature of 40°C to 100°C for a time of 15 minutes to 1 hour. Thus, the photo - electric conversion layer 4 is formed. When coating the mixed solution using the spin - coating method, a poor solvent can also be dropped into the spin - coating solution. Examples of the poor solvent are toluene, chlorobenzene, or diethyl ether.

[0148] The mixed solution can also contain a quenching substance such as tin fluoride. The concentration of the quenching substance can be 0.05 mol / L to 0.4 mol / L. By the quenching substance, the generation of defects in the photo - electric conversion layer 4 can be suppressed. The reason for the generation of defects in the photo - electric conversion layer 4 is, for example, the increase in Sn vacancies caused by the increase in the amount of Sn 4+ due to the increase in the amount.

[0149] A hole transport layer 5 is formed on the photoelectric conversion layer 4. Examples of methods for forming the hole transport layer 5 are coating or printing. Examples of coating methods are doctor blade method, rod coating method, spray method, dip coating method or spin coating method. An example of printing method is screen printing method. It is also possible to mix a plurality of materials to obtain the hole transport layer 5, and then pressurize or sinter the hole transport layer 5. When the material of the hole transport layer 5 is an organic low molecular weight body or an inorganic semiconductor, the hole transport layer 5 can also be made by vacuum evaporation method.

[0150] Finally, the second electrode 6 is formed on the hole transport layer 5. In this way, the solar cell 100 is obtained. The second electrode 6 can be formed by a CVD method or a sputtering method.

[0151] Figure 3 A cross-sectional view showing a modified example of the solar cell according to the embodiment. Figure 2 Unlike the solar cell 100 shown, the solar cell 200 includes a porous layer 7 .

[0152] Figure 3 In the solar cell 200 shown, the first electrode 2, the porous layer 7, the electron transport layer 3, the photoelectric conversion layer 4, the hole transport layer 5 and the second electrode 6 are sequentially stacked on the substrate 1. The porous layer 7 includes a porous body. The porous body includes vacancies. The solar cell 200 may also be without the substrate 1. The solar cell 200 may also be without the hole transport layer 5.

[0153] The vacancies contained in the porous layer 7 are continuous from the portion in contact with the first electrode 2 to the portion in contact with the electron transport layer 3. The vacancies contained in the porous layer 7 are filled with the material of the electron transport layer 3. Since the first electrode 2 is in contact with the electron transport layer 3, electrons move directly from the electron transport layer 3 to the first electrode 2.

[0154] Next, the basic effects of the solar cell 200 are described. When light is irradiated to the solar cell 200, the photoelectric conversion layer 4 absorbs the light and generates excited electrons and holes. The excited electrons move to the electron transport layer 3. And the holes generated in the photoelectric conversion layer 4 move to the hole transport layer 5. As described above, since the electron transport layer 3 and the hole transport layer 5 are electrically connected to the first electrode 2 and the second electrode 6, respectively, current is extracted from the first electrode 2 and the second electrode 6, which function as the negative electrode and the positive electrode, respectively.

[0155] The porous layer 7 makes it easy to form the photoelectric conversion layer 4. The electron transport layer 3 formed on the porous layer 7 can cover the surface and vacancy walls of the porous layer 7. Since the thickness of the electron transport layer 3 is small, the shape of the surface and vacancies of the porous layer 7 can be maintained. At this time, the material of the photoelectric conversion layer 4 also invades the vacancy inside the porous layer 7 covered by the electron transport layer 3. Therefore, the possibility of the material of the photoelectric conversion layer 4 being bounced off or agglomerated on the surface of the electron transport layer 3 is reduced. Therefore, the porous layer 7 becomes the foothold of the photoelectric conversion layer 4, and the photoelectric conversion layer 4 can be formed as a uniform film. The photoelectric conversion layer 4 can be formed by applying a solution on the electron transport layer 3 using a spin coating method and heating it.

[0156] Light scattering occurs due to the porous layer 7. Therefore, the optical path length of light passing through the photoelectric conversion layer 4 can be increased. The increase in the optical path length can increase the amount of electrons and holes generated in the photoelectric conversion layer 4.

[0157] The solar cell 200 can be produced by the same method as the solar cell 100. The porous layer 7 is formed on the first electrode 2 by, for example, a coating method.

[0158] (Porous layer 7)

[0159] The porous layer 7 serves as a base for forming the photoelectric conversion layer 4. The porous layer 7 does not hinder the movement of electrons from the photoelectric conversion layer 4 to the first electrode 2.

[0160] The porous layer 7 includes a porous body. An example of a porous body is a porous body in which insulating or semiconductor particles are connected. Examples of insulating particles are aluminum oxide or silicon dioxide. Examples of semiconductor particles are inorganic semiconductor particles. Examples of inorganic semiconductors are metal oxides (including perovskite oxides), metal sulfides or metal chalcogenides. Examples of metal oxides are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si or Cr. TiO2 is preferred. Examples of perovskite oxides are SrTiO3 or CaTiO3. Examples of metal sulfides are CdS, ZnS, In2S3, SnS, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2 or Cu2S. Examples of metal chalcogenides are CdSe, CsSe, In2Se3, WSe2, HgS, SnSe, PbSe or CdTe.

[0161] The thickness of the porous layer 7 can be 0.01 micrometers to 10 micrometers, or 0.1 micrometers to 1 micrometer. The surface roughness of the porous layer 7 can be very large. Specifically, the surface roughness coefficient given by the effective area / projected area can be 10 or more, or 100 or more. In addition, the projected area refers to the area of ​​the shadow formed behind the object when the object is illuminated from the front. The effective area refers to the actual surface area of ​​the object. The effective area can be calculated from the volume obtained by the projected area and thickness of the object and the specific surface area and volume density of the material constituting the object. The specific surface area is measured, for example, by the nitrogen adsorption method.

[0162] (Example)

[0163] The present disclosure will be described in more detail below with reference to the examples. As described below, in Examples 1 to 5 and Comparative Examples 1 to 4, solar cells having an electron transport layer and a photoelectric conversion layer containing a perovskite compound were prepared. Furthermore, the characteristics of each solar cell were evaluated. Each solar cell in Examples 1 to 5 and Comparative Examples 1 to 4 has Figure 2 The perovskite solar cell shown is a perovskite solar cell with the same structure as the perovskite solar cell 100 .

[0164] [Example 1]

[0165] A glass substrate (manufactured by Nippon Sheet Glass Co., Ltd.) having an indium-doped SnO2 layer on its surface was prepared. The glass substrate and the SnO2 layer functioned as a substrate 1 and a first electrode 2, respectively. The glass substrate had a thickness of 1 mm.

[0166] As a target, niobium oxide represented by the chemical formula Nb2O5 (produced by Toyoshima Seisakusho) is used. A film is formed on the SnO2 layer of the above-mentioned glass substrate at room temperature by sputtering. Nitrogen (flow rate: 1 sccm), oxygen (flow rate: 0.1 sccm) and argon (flow rate: 10 sccm) are supplied to the chamber. The pressure in the chamber during sputtering is 0.5 Pa. The RF power supplied to the target is 100 W. The treatment of the target using the sputtering method is carried out for 1 and a half minutes under the above conditions. In this way, an electron transport layer 3 composed of a niobium oxynitride film is formed. The electron transport layer 3 has a thickness of 8 nanometers. In this way, a sample for evaluation is prepared. The prepared sample is transported from an atmospheric atmosphere to a nitrogen atmosphere.

[0167] A coating solution containing SnI2, SnF2 and FAI (all made by Sigma-Aldrich) is prepared. The solvent of the coating solution is a mixed solvent of DMSO and DMF. The volume ratio of DMSO and DMF in the mixed solvent is 1:1. The concentration of SnI2 in the coating solution is 1.2 mol / L. The concentration of SnF2 in the coating solution is 1.2 mol / L. The concentration of FAI in the coating solution is 1.2 mol / L. Next, 80 microliters of the coating solution is applied to the electron transport layer 3 by spin coating. In this way, a coating film is formed. The formation of the coating film is carried out inside the glove box. The inside of the glove box is filled with N2. The thickness of the coating film is 500 nm. Next, the coating film is fired at 120°C and 30 minutes. In this way, a photoelectric conversion layer 4 is formed. A hot plate is used for firing. The photoelectric conversion layer 4 formed mainly contains a tin-based perovskite compound of FASnI3.

[0168] Next, 80 microliters of a toluene solution containing PTAA (manufactured by Sigma-Aldrich) at a concentration of 10 mg / mL was applied to the photoelectric conversion layer 4 by spin coating, thereby forming a hole transport layer 5. The hole transport layer 5 was formed inside a glove box. The thickness of the hole transport layer 5 was confirmed by analyzing the cross section using a scanning electron microscope (hereinafter sometimes referred to as "SEM", Helios G3 manufactured by FEI).

[0169] Finally, a gold film with a thickness of 120 nm is deposited on the hole transport layer 5 by evaporation. In this way, the second electrode 6 is formed. After that, an ultraviolet curing resin (Nagasechemtex Co., Ltd., model: Model XNR5516Z-B1) is attached around the portion where the second electrode 6 is formed in a nitrogen atmosphere, and nitrogen sealing is performed thereon using glass. Then, it is transported from the nitrogen atmosphere to the air atmosphere. Next, ultraviolet rays are irradiated for 15 minutes to cure the ultraviolet curing resin and complete the sealing. In this way, the solar cell of Example 1 is obtained.

[0170] [Example 2]

[0171] In Example 2, nitrogen (flow rate: 5 sccm), oxygen (flow rate: 0.1 sccm) and argon (flow rate: 10 sccm) were supplied to the chamber during the formation of the electron transport layer 3. The solar cell of Example 2 was obtained by the same method as Example 1 except for the above.

[0172] [Example 3]

[0173] In Example 3, nitrogen (flow rate: 10 sccm), oxygen (flow rate: 0.1 sccm) and argon (flow rate: 5 sccm) were supplied to the chamber during the formation of the electron transport layer 3. The solar cell of Example 3 was obtained by the same method as Example 1 except for the above.

[0174] [Example 4]

[0175] In Example 4, tin oxide represented by the chemical formula SnO2 (manufactured by Toyoshima Seisakusho) was used as a target in the formation of the electron transport layer 3, and nitrogen gas (flow rate: 10 sccm), oxygen gas (flow rate: 0.1 sccm) and argon gas (flow rate: 5 sccm) were supplied to the chamber. Except for this, the solar cell of Example 4 was obtained by the same method as Example 1.

[0176] [Example 5]

[0177] In Example 5, tin oxide represented by the chemical formula SnO2 (manufactured by Toyoshima Seisakusho) was used as a target in the formation of the electron transport layer 3, and nitrogen gas (flow rate: 10 sccm), oxygen gas (flow rate: 0.1 sccm) and argon gas (flow rate: 1 sccm) were supplied to the chamber. Except for this, the solar cell of Example 5 was obtained by the same method as Example 1.

[0178] [Comparative Example 1]

[0179] In Comparative Example 1, nitrogen gas was not supplied to the chamber during the formation of the electron transport layer 3. Except for this, the same method as in Example 1 was used to obtain a solar cell of Comparative Example 1.

[0180] [Comparative Example 2]

[0181] In Comparative Example 2, tin oxide represented by the chemical formula SnO2 (produced by Toyoshima Seisakusho) was used as a target in forming the electron transport layer 3, and nitrogen gas was not supplied to the chamber. Except for this, the solar cell of Comparative Example 2 was obtained by the same method as Example 1.

[0182] [Comparative Example 3]

[0183] In Comparative Example 3, titanium oxide represented by the chemical formula Ta2O5 (produced by Toyoshima Seisakusho) was used as a target in the formation of the electron transport layer 3, and nitrogen gas was not supplied to the chamber. Except for this, the solar cell of Comparative Example 3 was obtained by the same method as in Example 1.

[0184] [Comparative Example 4]

[0185] In Comparative Example 4, titanium oxide represented by the chemical formula Ta2O5 was used as a target in the formation of the electron transport layer 3, and nitrogen (flow rate: 5 sccm), oxygen (flow rate: 0.1 sccm) and argon (flow rate: 10 sccm) were supplied to the chamber. Except for this, the solar cell of Comparative Example 4 was obtained by the same method as in Example 1.

[0186] [Determination of composition]

[0187] In each example and comparative example, the composition of the electron transport material contained in the electron transport layer 3 contained in the sample was specifically identified using an XPS measuring device (manufactured by Ulvac-Phi Co., Ltd., trade name: PHI 5000 Versa Probe). AlKα rays were used as an X-ray source. The N / O ratio was determined by this measurement.

[0188] [Measurement of electron density]

[0189] In Examples 1 to 4 and Comparative Examples 1 to 3, the electron density of the electron transport layer 3 included in the samples was calculated from the Fermi energy measured by the XPS method and the transmittance measurement method.

[0190] For the electron transport layer 3 included in each sample, the value of the energy difference between the upper end of the valence band and the Fermi energy was obtained using an XPS measuring apparatus (manufactured by Ulvac-Phi Co., Ltd., trade name: PHI 5000 Versa Probe).

[0191] The transmittance of the electron transport layer 3 included in each sample was measured using a transmittance measuring device (manufactured by Shimadzu Corporation, trade name: SlidSpec-3700)). Next, the band gap value of each electron transport layer 3 was obtained from the measured transmittance.

[0192] Based on the difference between the upper end of the valence band and the Fermi energy and the value of the band gap thus obtained, the energy difference between the lower end of the conduction band of the electron transport layer 3 and the Fermi energy is calculated.

[0193] The difference between the lower end of the conduction band and the Fermi energy (E C -E F ) is introduced into the following formula (1). Then the electron density (n) is obtained.

[0194] [Mathematical formula 1]

[0195]

[0196] In the above formula (1), N C is the state density at the lower end of the conduction band, which is 2.2×10 18 cm -3 T is the temperature, which is 300 K. The value of k is the Boltzmann constant.

[0197] [Calculation of electrical conductivity]

[0198] The value of the electron density n obtained in the above equation (1) is substituted into the following equation (2). In this way, the electrical conductivity σ is obtained.

[0199] σ=qnμ(2)

[0200] In the above formula (2), the value of q is the basic charge. The value of μ is the carrier mobility. Here, 0.291 cm 2 / Vs (i.e., the value of carrier mobility possessed by the oxide film formed by sputtering).

[0201] [Evaluation of Photoelectric Conversion Efficiency]

[0202] The solar cells of Examples and Comparative Examples were irradiated with a solar light simulator (spectrometer: BPS X300BA) having a power of 100 mW / cm 2 The photoelectric conversion efficiency of each solar cell was measured using simulated sunlight of illumination.

[0203] Table 1 shows the following contents in the embodiments and comparative examples:

[0204] (i) In the production of the electron transport layer, the target material used, the presence or absence of nitrogen gas, and the materials contained in the produced electron transport layer;

[0205] (ii) a photoelectric conversion material contained in the photoelectric conversion layer;

[0206] (iii) the ratio N / O of the electron transport layer;

[0207] (iv) the energy difference between the lower end of the conduction band in the electron transport layer and the Fermi energy;

[0208] (v) electron density of the electron transport layer;

[0209] (vi) conductivity of the electron transport layer;

[0210] and (vii) the photoelectric conversion efficiency of solar cells.

[0211] When comparing Examples 1 to 3 with Comparative Example 1, the electron transport layer comprising niobium oxynitride has an increased electron density and improved photoelectric conversion efficiency compared to the electron transport layer comprising niobium oxide to which no nitrogen is added. In addition, when comparing Example 1 and Example 2, when the ratio N / O is in the range of 0.05 to 0.28, as the nitrogen composition in the electron transport layer increases, the electron density increases and the photoelectric conversion efficiency improves. Similarly, when comparing Example 4 and Comparative Example 2, the electron transport layer comprising tin oxynitride has an increased electron density and improved photoelectric conversion efficiency compared to the electron transport layer comprising tin oxide to which no nitrogen is added. Therefore, compared with oxides, oxynitrides have a higher electron density. As a result, an electron transport layer comprising oxynitrides can realize a solar cell with improved photoelectric conversion efficiency.

[0212] On the other hand, when comparing Example 1 with Comparative Example 4, it can be seen that when titanium oxynitride is used as an electron transport material, it lacks electron conductivity. Therefore, the photoelectric conversion function is hindered and it will not function as a solar cell. When an oxide such as titanium oxide in Comparative Example 5, which lacks electron conductivity and does not function as an electron transport layer, is used as a sputtering target, even if nitrogen is added to make an oxynitride, the electron conductivity of the oxynitride is as lacking as that of the oxide. Therefore, this oxynitride will not function as an electron transport layer. In addition, considering the photoelectric conversion efficiency of Comparative Examples 3 and 4, it is inferred that the conductivity in the electron transport layer of Comparative Example 4 is the same as the conductivity in the electron transport layer of Comparative Example 3. From the above, by using an oxynitride obtained by adding nitrogen to an oxide having electron transport properties such as niobium oxide or tin oxide in an electron transport layer, a solar cell with high photoelectric conversion efficiency can be achieved.

[0213] Table 1

[0214]

[0215] Industrial Applicability

[0216] The solar cell of the present disclosure is useful as a solar cell installed on a roof, for example.

[0217] Explanation of symbols

[0218] 1 substrate

[0219] 2 1st electrode

[0220] 3 Electron transport layer

[0221] 4 Photoelectric conversion layer

[0222] 5. Hole Transport Layer

[0223] 6 1st electrode

[0224] 7 Porous layer

[0225] 100, 200 solar cells

Claims

1. A solar cell comprising: 1st electrode; The second electrode; a photoelectric conversion layer disposed between the first electrode and the second electrode; and an electron transport layer disposed between the first electrode and the photoelectric conversion layer; in, At least one electrode selected from the first electrode and the second electrode has light-transmitting properties, The photoelectric conversion layer contains a perovskite compound composed of monovalent cations, divalent cations and halogen anions. The electron transport layer contains a metal oxynitride having electron conductivity, The metal oxynitride has a 1×10 -7 Conductivity above S / cm, The metal oxynitride is niobium oxynitride, and in the niobium oxynitride, a ratio (N / O) of the amount of N to the amount of O is 0.05 to 0.

28.

2. The solar cell according to claim 1, wherein: The monovalent cation includes a formamidinium cation.

3. The solar cell according to claim 1 or 2, wherein: The halogen anion comprises an iodide ion.

4. The solar cell according to claim 1 or 2, wherein: The divalent cation includes at least one selected from the group consisting of tin ions and lead ions.

5. The solar cell according to claim 1 or 2, wherein: A hole transport layer is provided between the second electrode and the photoelectric conversion layer.

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