JP2017054912A - Photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element capable of forming a film excellent in coverage at low temperature, suppressing the occurrence of leakage, and having long-term stability and high photoelectric conversion efficiency.SOLUTION: The photoelectric conversion device includes a light absorption layer containing a perovskite compound including an organic ammonium metal halide or a Cs metal halide. An electron transport layer located under the light absorption layer is made of amorphous TiOformed by an atomic layer deposition method, and the refractive index of the electron transport layer at 589 nm is 1.80 or more.SELECTED DRAWING: None

Description

  The present invention relates to a photoelectric conversion element.

  In recent years, solar cells that can directly convert light energy from the sun into electricity have attracted attention as one of renewable energy technologies. There are various types of solar cells, such as silicon, compound, and organic, depending on the semiconductor used as a raw material. Recently, research on perovskite solar cells using a compound with a crystal structure called perovskite (perovskite compound) The energy conversion efficiency approaching that of the mainstream silicon-based solar cells can be obtained.

As perovskite compounds, for example, various compositions such as transition metal oxides represented by the chemical formula ABO ₃ are known, but most of the conventional researches are related to lead-based perovskite compounds. For example, Patent Document 1 proposes a solar cell in which photoelectric conversion efficiency is improved by combining an inorganic hole transport layer with a light absorption layer made of a lead iodide-based layered perovskite compound.

JP 2014-175473 A

  As described above, solar cells using a perovskite compound are able to obtain higher energy conversion efficiency than in the early days of research, but from the viewpoint of practicality, the conversion efficiency is still further improved. It is also necessary to improve the device life.

  In order to exhibit the performance of the photoelectric conversion element over a long period of time, it is desired that the film thickness of the thin film layer constituting the element is uniform and the covering property is high. For example, when a defect occurs in the perovskite layer (light absorption layer), the underlying electron transport layer and the hole transport layer stacked on the perovskite layer are in direct contact with each other, resulting in leakage and variations in characteristics. Arise. In addition, if the surface flatness of the perovskite layer is low, the thickness of the hole transport layer cannot be secured, and the hole collection electrode (second electrode) laminated on the hole transport layer is in contact with the perovskite layer. A short circuit occurs, causing a decrease in photoelectric conversion efficiency.

  Recently, a new electronic device using a flexible substrate such as a functional film (for example, a transparent conductive film having an ITO thin film formed on a plastic film substrate) continuously formed on a plastic film by a roll-to-roll method. There is growing interest in the development of so-called flexible electronics. However, there are still problems to be solved in the development of a flexible perovskite solar cell using the roll-to-roll method. In particular, since the film forming conditions are limited due to the low heat resistance of the plastic film, further improvement of the film forming method is desired.

  Therefore, development of a photoelectric conversion element that does not require a high temperature process, can be easily manufactured, and has excellent performance is demanded.

  The present invention has been made in view of the circumstances as described above, can form a film with excellent coverage at low temperature, suppress the occurrence of leakage, has long-term stability, and has high photoelectric conversion. It aims at providing the photoelectric conversion element which has efficiency.

  As a result of intensive studies to achieve the above object, the present inventors have found that, among the thin film layers constituting the photoelectric conversion element, the correlation between the refractive index at a specific wavelength in the electron transport layer and the performance of the photoelectric conversion element. The inventors have conceived that the performance of the photoelectric conversion element can be improved by finding the relationship and controlling the density of the electron transport layer. Then, by stacking the electron transport layer constituting the photoelectric conversion element under a predetermined condition using an atomic layer deposition method, the electron transport layer is formed stably and with high coverage, whereby photoelectric conversion is performed. It has been found that the surface flatness of the thin film layer constituting the element is improved, the occurrence of leakage is suppressed, long-term stability is achieved, and high photoelectric conversion efficiency is obtained. It has also been found that a photoelectric conversion element employing such a configuration can be easily manufactured without requiring a high-temperature process.

  Based on these new findings, the present inventors have made further studies and completed the present invention.

That is, this invention includes the following aspects.
(1) A photoelectric conversion element comprising a light absorption layer containing an organic ammonium metal halide or Cs metal halide, wherein the electron transport layer located under the light absorption layer is made of amorphous TiO ₂ , and the electron transport The photoelectric conversion element characterized by the refractive index in 589 nm of a layer being 1.80 or more.
(2) The photoelectric conversion element according to (1), wherein the electron transport layer has a thickness of 5 to 100 nm.
(3) The photoelectric conversion element of (1) or (2), wherein the electron transport layer is an electron transport layer formed by laminating by an atomic layer deposition method.
(4) The photoelectric conversion element according to (3), wherein the atomic layer deposition method is a plasma ALD method, an ozone ALD method, or a thermal ALD method.
(5) The photoelectric conversion element according to any one of (1) to (4), wherein the electron transporting layer has a laminated structure composed of amorphous TiO ₂ layers having 50 to 2000 laminated layers.

  ADVANTAGE OF THE INVENTION According to this invention, the film-forming excellent in the covering property at low temperature is possible, generation | occurrence | production of a leak is suppressed, long-term stability is provided, and the photoelectric conversion element which has high photoelectric conversion efficiency is provided. Moreover, the photoelectric conversion element of this invention does not require a high temperature process, and can be manufactured simply.

FIG. 1 is an X-ray diffraction chart showing the results of analyzing the TiO ₂ thin film (electron transport layer) obtained under the production conditions of Example 1 using an X-ray diffractometer.

  Hereinafter, embodiments of the present invention will be described in detail. The description of the constituent elements described below is an example (representative example) of the embodiment of the present invention, and the specific form is not limited to these embodiments, and the design is within the scope not departing from the gist of the present invention. Any change or the like is included in the present invention.

<Light absorption layer>
The light absorption layer is a layer containing at least one perovskite compound. The light absorption layer may be a single layer or a multilayer. In the case of a multilayer, each layer may be a layer containing a perovskite compound, or at least one layer may be a layer containing a perovskite compound. In addition, a perovskite compound may be used individually by 1 type, and may be used in combination of 2 or more type.

  The perovskite compound has a periodic table group 1 element or cationic organic group A, a metal atom M other than the periodic table group 1 element, and an anionic atom X. In the perovskite compound, the periodic table group I element or the cationic organic group A, the metal atom M, and the anionic atom X are each a cation (hereinafter sometimes referred to as “cation A”), a metal cation in the perovskite crystal structure. (Hereinafter, sometimes referred to as “metal cation M”) and anion (hereinafter also referred to as “anion X”).

  In the present invention, the cationic organic group refers to an organic group having a property of becoming a cation in a perovskite crystal structure. An anionic atom means an atom having a property of becoming an anion in a perovskite crystal structure.

  The perovskite compound used in the present invention is not particularly limited as long as it is a compound that can have a perovskite crystal structure containing the above constituent ions.

In the perovskite compound used in the present invention, the cation A is an organic cation composed of a cation of a group 1 element of the periodic table or a cationic organic group A. The cation A is preferably an organic cation, and more preferably an organic ammonium cation. The cation of the Group 1 element of the periodic table is not particularly limited, and for example, the cation (Li ⁺ , Na ⁺ , K ⁺ of each element of lithium (Li), sodium (Na), potassium (K), or cesium (Cs). Cs ⁺ ), and a cesium cation (Cs ⁺ ) is particularly preferable.

  In the perovskite compound used in the present invention, the metal cation M is not particularly limited as long as it is a cation of a metal atom M other than a group 1 element of the periodic table and a cation of a metal atom capable of taking a perovskite crystal structure. Examples of such metal atoms include calcium (Ca), strontium (Sr), cadmium (Cd), copper (Cu), nickel (Ni), manganese (Mn), iron (Fe), cobalt (Co), Examples include metal atoms of palladium (Pd), germanium (Ge), tin (Sn), lead (Pb), ytterbium (Yb), europium (Eu), and indium (In). Of these, the metal atom forming the metal cation is particularly preferably Pb or Sn. The metal atom may be one kind of metal atom or two or more kinds of metal atoms. In the case of two or more kinds of metal atoms, two kinds of Pb and Sn are preferable. In addition, the ratio of the metal atom at this time is not specifically limited.

  In the perovskite compound used in the present invention, the anion X represents an anion of the anionic atom X. This anion is preferably an anion of a halogen atom. As a halogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. are mentioned, for example. The anion X may be an anion of one kind of anionic atom or an anion of two or more kinds of anionic atoms. In the case of anions of two or more types of anionic atoms, two types of anions of halogen atoms, in particular, anions of chlorine atoms and iodine atoms, anions of bromine atoms and anions of iodine atoms are preferred. In addition, the ratio of the anion of the anionic atom at this time is not particularly limited.

  In one embodiment of the present invention, the light absorption layer is a layer containing an organic ammonium metal halide or Cs metal halide.

The organic ammonium constituting the organic ammonium metal halide is not particularly limited, and examples thereof include mono-substituted ammonium such as methyl ammonium, propyl ammonium, butyl ammonium, hexyl ammonium, octyl ammonium, cetyl ammonium, phenyl ammonium, benzyl ammonium, and phenethyl ammonium. (Preferably C _1-6 alkylammonium, more preferably methylammonium); disubstituted ammonium such as dimethylammonium, dipropylammonium, dibutylammonium, dihexylammonium, dioctylammonium, diphenylammonium, dibenzylammonium, diphenethylammonium (preferably _{C 1-6} dialkyl ammonium, more preferably dimethyl ammonium Um); trimethylammonium, tripropyl ammonium, tributyl ammonium, tri-hexyl ammonium, trioctyl ammonium, triphenyl ammonium, tribenzyl ammonium, trisubstituted ammonium (preferably C _1-6 trialkylammonium and triethylene phenethyl ammonium, more preferably Is trimethylammonium); tetramethylammonium, tetrapropylammonium, tetrabutylammonium, tetraoctylammonium, tetradecylammonium, tetraphenylammonium, tetrabenzylammonium, tetraphenethylammonium, trimethylbenzylammonium, decyltrimethylammonium, benzyl Cetyldimethylammonium Cetyl dimethyl ethyl ammonium, (preferably C _1-6 tetraalkylammonium, more preferably tetramethylammonium) 4-substituted ammonium such as phenyl trimethyl ammonium, and the like. Among these, from the viewpoints of intramolecular symmetry, dielectric constant, dipole moment and the like, monosubstituted ammonium is preferable, C _1-6 alkylammonium is more preferable, and methylammonium is further preferable.

  The metal constituting the organoammonium metal halide or Cs metal halide is not particularly limited, but a metal belonging to Groups 11 to 15 of the periodic table is preferable from the viewpoint of constituting a perovskite structure. Specifically, lead, indium, zinc, tin, silver, antimony, copper and the like are preferable, lead and tin are more preferable, and lead is more preferable.

  The halogen constituting the organic ammonium metal halide or Cs metal halide is not particularly limited, but iodine, chlorine, bromine and the like are preferable from the viewpoint of appropriate spread of electron cloud, electronegativity, charge density, ionicity, and the like. More preferred is iodine. One of these halogens may be contained in the organic ammonium metal halide or Cs metal halide, or two or more of them may be contained.

The organic ammonium metal halide satisfying such conditions is not particularly limited, but from the viewpoints of whether a perovskite structure can be formed, intramolecular symmetry, dielectric constant, dipole moment, etc., the general formula ( 1):
(RNH ₃ ) _n PbX _{(2 + n)}
[Wherein R represents a hydrocarbon group, X represents a halogen, and n is 1 or 2. ]
A monosubstituted ammonium lead halide represented by the formula is preferred.

The hydrocarbon group represented by R is not particularly limited as long as the monosubstituted ammonium lead halide can have a structure in which organic ammonium molecular layers and lead iodide layers are alternately stacked. However, a methyl group, a propyl group, Examples thereof include a butyl group, a hexyl group, an octyl group, a cetyl group, a phenyl group, a benzyl group, and a phenethyl group. A C _1-6 alkyl group such as a methyl group, a propyl group, a butyl group, and a hexyl group is preferable, and a methyl group is preferable. More preferred.

  The halogen represented by X is not particularly limited, but iodine, chlorine, bromine and the like are preferable, and iodine is more preferable.

  n preferably takes a value according to the type of R such that a mono-substituted ammonium lead halide can form a structure in which organic ammonium molecular layers and lead iodide layers are alternately stacked. For example, when R is a methyl group or the like, n is preferably 1, and when R is a hexyl group or a phenethyl group, n is preferably 2.

Specific examples of the monosubstituted ammonium lead halide satisfying such conditions include (CH ₃ NH ₃ ) PbI ₃ , (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ PbI ₄ , and (C ₁₀ H _7. CH ₂ NH ₃ ) ₂ PbI ₄ and (C ₆ H ₁₃ NH ₃ ) ₂ PbI _{4 and the} like. From the viewpoint of whether a perovskite structure can be formed, intramolecular symmetry, dielectric constant, dipole moment, etc. CH ₃ NH ₃ ) PbI _{3 and the} like are preferred. The said 1 substituted ammonium lead halide may be used individually by 1 type, and may be used in combination of 2 or more type.

In the present invention, the organic ammonium metal halide used in the light absorption layer is not limited to the monosubstituted ammonium lead halide described above, and various compounds can be used. For _{example, (CH 3 NH 3) PbCl} 3, (CH 3 NH 3) PbCl x I 3-x (0 <x <3), (CH 3 NH 3) PbBr 3, (C 2 H 5 NH 3) PbBr 3 , (CH ₃ NH ₃ ) Pb (I _1-x Br _x ) ₃ (0 <x <1), (C ₂ H ₅ NH ₃ ) Pb (I _1-x Br _x ) ₃ (0 <x <1) Etc. can also be used. _{Further, (CH 3 NH 3) SnCl} 3, (CH 3 NH 3) SnBr 3, CH 3 NH 3 SnI 3, CH 3 NH 3 SnIBr 2, CH 3 CH 2 NH 3 SnCl 3, CH 3 CH 2 NH 3 SnBr ₃ , CH ₃ CH ₂ NH ₃ SnI ₃ , CH ₃ CH ₂ NH ₃ SnIBr ₂ , (CH ₃ CH═NH ₂ ) SnCl ₃ , (CH ₃ CH═NH ₂ ) SnBr ₃ , and (CH ₃ CH═NH ₂ ) Organic ammonium tin (II) halides such as SnI ₃ can also be used.

Further, the Cs metal halide used in the light absorption layer is not particularly limited, and examples thereof include compounds represented by CsPbX ₃ , CsSnX _{3 and the} like (X represents halogen). , CsPbCl ₃ , CsPbBr ₃ , CsPbI ₃ , CsPbIBr ₂ , CsSnCl ₃ , CsSnBr ₃ , CsSnI ₃ , and CsSnIBr ₂ .

In the present invention, if necessary, general formula (2) similar to the perovskite structure: A ₂ SnX ₆ [wherein, A represents Cs, CH ₃ NH ₃ , or CH ₂ = CHNH ₂ , X represents I, Br or Cl is represented. A perovskite-like compound represented by the formula:

  Moreover, in this invention, the compound which used the halogen which comprises organic ammonium metal halide or Cs metal halide as characteristic groups, such as a thiocyanate group (SCN group), can also be used.

  Moreover, in this invention, it is good also as a tandem type | mold using the sensitizing dyes, such as a metal complex dye and an organic dye, for a light absorption layer in order to extend the absorption wavelength range of a light absorption layer. As the sensitizing dye, generally known sensitizing dyes can be used. For example, examples of the metal complex dye include a ruthenium metal complex dye and a phthalocyanine dye. Examples of organic dyes include cyanine dyes.

  The thickness of the light absorption layer is preferably 10 to 10,000 nm, more preferably 20 to 500 nm, and even more preferably 100 to 400 nm from the viewpoint that when the film is excessively thick, performance deterioration due to defects and peeling is likely to occur. When the light absorption layer is a multilayer, the total film thickness of the light absorption layer is preferably within the above range.

  The light absorption layer can be formed, for example, by applying a perovskite compound solution onto an electron transport layer described later, using a generally known method, and drying to form a film. For example, by employing a non-vacuum process such as a spin coating method, the photoelectric conversion element of the present invention can be manufactured more easily.

The perovskite compound solution may be a solution containing the perovskite compound itself, but a solution containing a cation A, a metal cation M and an anion X which are constituent ions of the perovskite compound, or a solution containing MX ₂ and AX. Preferably there is. For example, when the monosubstituted ammonium lead halide represented by the general formula (1) is used, a solution containing PbX ₂ and (RNH ₃ ) X can be obtained.

  In the photoelectric conversion element of the present invention, as described in detail below, since the surface flatness of the electron transport layer is excellent, the surface flatness of the light absorption layer laminated on the electron transport layer is also improved. It is expected to suppress defects in the light absorption layer.

<Electron transport layer>
In the photoelectric conversion element of the present invention, the electron transport layer is preferably formed under the light absorption layer.

The electron transport layer is preferably a layer containing a light-transmitting electron transport material (particularly a layer made of a light-transmitting electron transport material). The transparent electron transport material is not particularly limited, specifically, titanium oxide (TiO _2, etc.), tungsten oxide _{(WO 2, WO 3, W} 2 O 3 , etc.), zinc oxide (ZnO), One or more metal oxides such as strontium titanate (such as SrTiO ₃ ) and aluminum oxide (Al ₂ O ₃ ) can be used.

In one embodiment of the present invention, the electron transport layer can be made into an amorphous crystalline form using TiO ₂ . That is, in the photoelectric conversion element of the present invention, even if it is an electron transport layer formed under low-temperature film formation conditions (for example, 130 ° C. or less) that does not include a high-temperature process, generation of film defects and leakage are suppressed. Can do. The amorphous TiO ₂ layer is provided with other metal oxide layers such as Al ₂ O ₃ as a hole blocking layer or ZnO to improve electron transport properties. May be.

In the above embodiment, the electron transport layer made of amorphous TiO ₂ has a refractive index of 1.80 or more at 589 nm. Among these, the refractive index is preferably in the range of 2.00 to 2.52, and more preferably in the range of 2.30 to 2.52. When the refractive index at 589 nm of the electron transport layer made of amorphous TiO ₂ is in the above range, the electron transport property is improved by the excellent denseness of the electron transport layer, and a photoelectric conversion element having excellent conversion efficiency is obtained. be able to. On the other hand, when the refractive index is less than 1.80, the denseness of the electron transport layer is impaired, the electron transport property is lowered, and the conversion efficiency of the photoelectric conversion element is lowered. That is, in the present invention, since the density of the electron transport layer is controlled, the occurrence of leakage is suppressed, and a photoelectric conversion element having long-term stability and high photoelectric conversion efficiency can be obtained.

The thickness of the electron transport layer is preferably 5 to 100 nm, more preferably 5 to 50 nm, and even more preferably 10 to 40 nm. By setting the thickness of the electron transport layer within the above range, leakage can be more reliably suppressed. For example, the thickness of the electron transport layer made of amorphous TiO ₂ can be 5 to 100 nm.

  Next, a method for forming the electron transport layer will be described.

  In the present embodiment, the electron transport layer is preferably formed using an atomic layer deposition (ALD) method. More specifically, for example, the electron transport layer can be formed by repeating the film formation reaction at 50 to 130 ° C. for 50 to 2000 cycles using the ALD method. Thereby, the density of the electron transport layer is controlled and the surface flatness is improved.

In the ALD method, two kinds of source gases (precursor gases) mainly composed of elements constituting the thin film to be formed are alternately introduced into the chamber, and the source gases are adsorbed on the substrate surface. After removing N ₂ with N ₂ , another raw material gas such as water is introduced into the adsorbed monomolecule to cause a thermal reaction, or active oxygen plasma or ozone gas is introduced to react to form a reaction product film one atomic layer at a time. Then, this is repeated to form a thin film having a desired film thickness (for example, several tens of nm). The ALD thin film formed by this method is dense and is formed following the crack and shape of the substrate because of its high coverage, so that a barrier film having high barrier properties can be obtained stably. Is suitable.

  The ALD method can be classified according to the reaction activation means and the oxidant used, and a thermal ALD method, an ozone ALD method, a plasma ALD method (PEALD: Plasma Enhanced ALD) and the like are known. The thermal ALD method is a method of accelerating the reaction of the reaction gas by heating. In this specification, unless otherwise specified, the ALD method refers to an ALD method using water as an oxidizing agent. The ozone ALD method is a method of promoting reaction of a reaction gas by heating using ozone as an oxidizing agent. The plasma ALD method is a method of promoting reaction of a reaction gas by oxygen plasma (plasmaized oxygen).

In the thermal ALD method, it is necessary to complete the process of forming a single atomic layer in a short time of less than 1 second. Therefore, adsorption of water having a large adsorbing power to a source gas and unnecessary gas Complete removal may be difficult. On the other hand, the ozone ALD method and the plasma ALD method do not use water, and thus are free from the above-described problems and are excellent in terms of productivity. In the ALD method that does not use water, it is not necessary to remove the water adsorbed on the substrate, and the film is formed under a low temperature condition of, for example, 50 to 130 ° C., preferably 70 to 100 ° C., more preferably 70 to 90 ° C. It is possible to form a film on a flexible substrate having a low softening temperature such as PET, which is preferable. In particular, the plasma ALD method using oxygen plasma with high reaction activity is preferable because high-speed film formation is possible. In the ozone ALD method, the organic polymer such as olefin attached to the surface of the electron transport material such as TiO ₂ is decomposed (cracked) by ozone oxidation, and converted into a lower molecular weight hydrophilic carbonyl or the like for removal (cleaning). Therefore, it has the effect of suppressing the occurrence of defects in the coating film of the electron transport material in the electron transport layer, and the leakage due to the defects is reduced, thereby improving the conversion efficiency of the photoelectric conversion element and extending the life of the element. Is possible and preferable.

The number of cycles of the film formation reaction by the ALD method can be appropriately adjusted according to the type of the electron transport material used as the electron transport layer, the desired film thickness of the electron transport layer, and the like. For example, when forming an electron transport layer made of amorphous TiO _2, it is preferable to repeat 50 to 2000 cycles, more preferably 100 to 1500 cycles, and even more preferably 150 to 1000 cycles. Thereby, the density of the electron transport layer is controlled and the surface flatness is improved.

  The number and thickness of the electron transport materials in the electron transport layer can be measured, for example, by observing a cross section of the electron transport layer formed by the ALD method with an electron microscope (TEM, FESEM, etc.). The film thickness of the electron transport layer can also be measured using a palpation step meter, a light interference film thickness meter, a spectroscopic ellipsometer, or the like. In the present invention, under the condition that a film can be formed by applying the ALD method, the number of cycles of the film formation reaction by the ALD method and the number of stacked electron transport materials have a correlation indicating linearity. It has been confirmed that

<Porous electron transport layer>
In the photoelectric conversion element of the present invention, a porous electron transport layer having a porous structure may be formed between the light absorption layer and the electron transport layer. In the present specification, the term “electron transport layer” simply means that the “porous electron transport layer” is not included.

  With respect to the porous electron transport layer, the porous structure is not particularly limited, but a granular body, a linear body (a linear body: a needle shape, a tube shape, a column shape, etc.), etc. are aggregated to form a whole. It preferably has a porous property. The pore size is preferably nanoscale. By having a porous structure, since it is nanoscale, the active surface area of the light absorption layer can be remarkably increased, the photoelectric conversion efficiency can be improved, and a porous electron transport layer excellent in electron collection can be obtained.

The porous electron transport layer is preferably a layer containing a light transmissive porous electron transport material (a layer made of a light transmissive porous electron transport material). The porous electron-transporting material of the translucent, is not particularly limited, specifically, titanium oxide (TiO _2, etc.), tungsten oxide _{(WO 2, WO 3, W} 2 O 3 , etc.), zinc oxide (ZnO ), Niobium oxide (Nb ₂ O ₅ etc.), tantalum oxide (Ta ₂ O ₅ etc.), yttrium oxide (Y ₂ O ₃ etc.), strontium titanate (SrTiO ₃ etc.), etc. Can be used. In addition, when using a semiconductor, the donor may be doped. Thereby, the porous electron transport layer becomes a window layer for introduction into the light absorption layer, and the electric power obtained from the light absorption layer can be taken out more efficiently. When adopting titanium oxide (TiO ₂ or the like) as the light-transmitting porous electron transport material, the crystal form is preferably anatase type.

  The thickness of the porous electron transport layer is preferably about 10 to 2000 nm, and more preferably about 20 to 1500 nm. By setting the film thickness of the porous electron transport layer within the above range, electrons from the light absorption layer can be collected more reliably.

  If the porous electron transport layer is formed by a non-vacuum process such as a screen printing method, for example, the photoelectric conversion element of the present invention can be more easily produced. In addition, there is an advantage that the area can be easily increased and the quality is stabilized.

<First electrode layer: translucent conductive layer>
In the photoelectric conversion element of this invention, it is preferable that a translucent conductive layer is formed under an electron carrying layer.

  The translucent conductive layer is preferably, for example, a layer containing a transparent conductive oxide (particularly a layer made of a transparent conductive oxide). Examples of the transparent conductive oxide include fluorine-doped tin oxide (FTO), indium tin oxide (ITO), gallium-doped zinc oxide (GZO), aluminum-doped zinc oxide (AZO), and niobium-doped titanium oxide ( One or more of TNO), indium zinc oxide (IZO), and the like can be used. Moreover, you may use what laminated | stacked aluminum dope zinc oxide (AZO) and Ag alternately (AZO / Ag / AZO). Thereby, a translucent conductive layer becomes a window layer for introducing into a light absorption layer, and the electric power obtained from the light absorption layer can be taken out efficiently.

  The thickness of the translucent conductive layer is preferably about 0.01 to 10.0 μm, and more preferably about 0.05 to 1.0 μm. By setting the film thickness of the translucent conductive layer within the above range, the sheet resistance can be reduced, and as a result, the series resistance of the photoelectric conversion element can be reduced, so that the fill factor characteristic can be maintained.

<Translucent substrate>
In the photoelectric conversion element of the present invention, the translucent substrate is preferably formed under the translucent conductive layer.

  Although it does not restrict | limit especially as a translucent board | substrate, For example, it is preferable to comprise from glass, plastics, etc. Thereby, it can become a window layer for introducing light into the light absorption layer.

  In the photoelectric conversion element of the present invention, the translucent substrate is more preferably a flexible translucent resin substrate. Thereby, the element manufacture by a roll to roll system is realizable.

  Examples of organic materials for forming a flexible translucent resin substrate include acrylic acid ester, methacrylic acid ester, polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), polycarbonate (PC), polyarylate, poly List vinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polystyrene (PS), nylon (Ny), aromatic polyamide, polyetheretherketone, polysulfone, polyethersulfone, polyimide, polyetherimide, etc. Can do. As the light-transmitting resin substrate, a substrate formed of these organic materials can be used as a single layer or by stacking two or more layers. The translucent resin substrate can be generally produced by a known method, and may be an unstretched film or a stretched film.

  Although the thickness of a translucent board | substrate is not specifically limited, It is preferable to set it as about 0.1-5.0 mm.

  For example, a substrate with a transparent conductive film such as a glass with an indium tin oxide (ITO) film or a glass with a fluorine-doped tin oxide (FTO) film can be used as the light-transmitting substrate and the light-transmitting conductive layer.

<Hole transport layer>
In the photoelectric conversion element of this invention, the positive hole transport layer may be further provided on the light absorption layer.

Examples of the material used for the hole transport layer include selenium, iodide such as copper iodide (CuI), cobalt complex such as layered cobalt oxide, CuSCN, molybdenum oxide (MoO ₃ etc.), nickel oxide (NiO). Etc.), 4CuBr · 3S (C ₄ H ₉ ), organic hole transport material, and the like.

  Examples of the organic hole transport material include polythiophene derivatives such as poly-3-hexylthiophene (P3HT) and polyethylenedioxythiophene (PEDOT), 2,2 ′, 7,7′-tetrakis- (N, N-di-), and the like. Fluorene derivatives such as p-methoxyphenylamine) -9,9′-spirobifluorene (spiro-MeO-TAD), carbazole derivatives such as polyvinylcarbazole, triphenylamine derivatives, diphenylamine derivatives, polysilane derivatives, polyaniline derivatives, and the like. It is done.

  The thickness of the hole transport layer is not particularly limited, but is preferably about 0.01 to 10 μm.

  The hole transport layer is preferably formed by a non-vacuum process such as a vapor deposition method, a spray method, or a dip method.

<Second electrode layer>
In the photoelectric conversion element of this invention, it is preferable to provide a 2nd electrode layer on a positive hole transport layer.

  The material constituting the second electrode layer is not particularly limited, but for example, carbon, gold, platinum, palladium, rhodium, tungsten, molybdenum, tantalum, titanium, niobium, indium tin oxide, fluorine-doped tin oxide, aluminum-doped Zinc oxide, gallium-doped zinc oxide, and the like are preferable. In addition, alloys of metals such as gold, platinum, palladium, rhodium, tungsten, molybdenum, tantalum, titanium, and niobium are also preferably used.

  The thickness of the second electrode layer is not particularly limited, but is preferably about 0.01 to 2.0 μm.

  In the present invention, the surfaces of the first electrode layer and the electron transport layer are preferably subjected to UV ozone treatment or oxygen plasma treatment. Thereby, organic substances are removed from the surface, the surface is activated, and the film forming accuracy of the thin film formed thereon is improved.

  Moreover, it is preferable that the photoelectric conversion element of this invention is sealed so that the area | region which performed film-forming (vapor deposition) of the translucent board | substrate may be sealed with a sealing material. As a result, it is possible to improve the durability of the photoelectric conversion element and to increase the lifetime. As the sealing material, various generally known materials such as glass and resin can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to these Examples.

<Example 1>
(Preparation of photoelectric conversion element)
As follows, as the cell structure, to produce a solar cell element of _{<glass / ITO / TiO 2 /} (CH 3 NH 3) PbI 3 / Spiro-OMeTAD / Au> structure. Note that structures separated by slashes (/) mean that they are in that order. In this example, glass, ITO, TiO ₂ , (CH ₃ NH ₃ ) PbI ₃ , Spiro-OMeTAD, and Au are It means that the layers are formed in order.

  First, the surface of a glass substrate with an indium tin oxide (ITO) film (0.7 mm glass / 150 nm ITO) (manufactured by Geomatech) was subjected to UV ozone treatment for 10 minutes.

Next, using titanium tetraisopropoxide (TTIP) (manufactured by Japan Advanced Chemicals) as a raw material, a film formation reaction is performed by a plasma ALD method (Model OZONE manufactured by Forall, output 80 W of plasma generator). An electron transport layer (thickness 20 nm) made of TiO ₂ was formed by repeating 330 cycles at 0 ° C., and this surface was subjected to oxygen plasma treatment. As will be described later, the crystalline state of TiO ₂ was amorphous. In this example, the film thickness of the formed thin film layer was measured by a palpation step meter.

Next, in the same manner as described in the literature (Y. Yang et al., “Moisture assisted perovskite film growth for high performance solar cell”, Applied Physics Letters 105, 183902 (2014)), on the electron transport layer, A light absorption layer (thickness 300 nm) made of a CH ₃ NH ₃ PbI ₃ perovskite compound was formed.

  Next, Spiro-OMeTAD (72.3 mg, 0.059 mmol) as a hole transport material, lithium-bis (trifluoromethanesulfonyl) imide (LiTFSI, 9.1 mg, 0.0317 mmol), [Tris (2- ( 1H-pyrazol-1-yl) -4-tert-butylpyridine) cobalt (III) tris (bis (trifluoromethylsulfonyl) imide)] ([Tris (2- (1H-pyrazol-1-yl) -4- tert-butylpyridine) cobalt (III) Tris (bis (trifluoromethylsulfonyl) imide)], 8.7 mg, 0.0058 mmol) was dissolved in chlorobenzene (1 mL), and t-butylpyridine (TBP, 28.8 μL, 0.195 mmol). ) And stirred for 10 minutes to prepare a hole transport layer solution. 90 μL of this hole transport layer solution was placed on the light absorption layer, allowed to stand for 20 seconds, and then applied by spin coating (slope 5 sec, 500 rpm 5 sec, slope 5 sec, 4000 rpm 30 sec, slope 5 sec) and heated to 70 ° C. The hole transport layer (film thickness 400 nm) was formed into a film by drying on the hot plate for 30 minutes.

  Next, Au was vapor-deposited on the hole transport layer by a vapor deposition method to produce a second electrode layer (film thickness 100 nm).

Next, in the glove box substituted with nitrogen, a hygroscopic sheet was attached to the concave portion of the cap glass, a UV curable resin was applied around the concave portion of the cap glass with a dispenser, and a substrate was formed (evaporated) Was sealed so as to be sealed with a cap glass, and UV light was irradiated with a UV lamp to cure the UV curable resin, followed by sealing.
In this way, a photoelectric conversion element (solar cell element) was obtained.

FIG. 1 is an X-ray diffraction chart showing the results of analyzing a TiO ₂ thin film (electron transport layer) obtained under the production conditions of this example using an X-ray diffractometer (manufactured by Rigaku Corporation, XtaLAB mini). . A sample for measurement was prepared by forming a TiO ₂ layer on a slide glass (manufactured by Matsunami Glass Industry Co., Ltd., model number S011110, size 76 mm × 26 mm, thickness 1 mm) by the same method as described above. As is generally known, a diffraction peak characteristic at 2θ = 20 to 30 ° is seen in TiO _{2 of} anatase type crystal, but in the XRD chart shown in FIG. 1, it is seen around 2θ = 20 to 30 °. It can be seen that the diffraction pattern obtained is low in intensity and broad. This, in this embodiment, it was confirmed that the electron-transporting layer is composed of TiO ₂ amorphous. As a preliminary experiment, when the above measurement sample was further heated at 90 ° C. for 30 minutes and then X-ray diffraction analysis was performed, an XRD chart similar to FIG. 1 was obtained, and the TiO ₂ thin film had an amorphous crystalline state. It was confirmed that it was maintained.

Moreover, the refractive index in 589 nm of the electron carrying layer was measured using the spectroscopic ellipsometer (M-2000 by JA Woollam). The measurement sample was prepared in the same manner as the above X-ray diffraction analysis, and the measurement conditions were as follows. In the calculation of the optical constant, for example, the measured spectrum of the phase difference Δ and the amplitude reflectance ψ is calculated from a calculation model (in this example, an optical model of TiO ₂ / glass substrate) (Δ, ψ) and Comparison is made and fitting is performed using a least square method or the like so as to approach the measured values (Δ, ψ).
(Measurement condition)
Incident angle: 50, 60, 70 degrees Measurement wavelength range: 195 nm to 1680 nm
Analysis software: WVASE32
Beam diameter: about 2 mm × 8 mm.

<Example 2>
The surface of a glass substrate with indium tin oxide (ITO) film (0.7 mm glass / 150 nm ITO) (manufactured by Geomatech) was subjected to UV ozone treatment for 10 minutes.

Then, using tetrakisdimethylaminotitanium (TDMAT) (manufactured by Japan Advanced Chemicals) as a raw material, the film formation reaction was repeated 330 cycles at 120 ° C. by TiO2 by the ozone ALD method (Lab Nano ^™ 9100 manufactured by Ensure Nanotech). _An electron transport layer (film thickness 20 nm) consisting of ₂ was formed, and this surface was treated with UV ozone.

  Next, on the electron transport layer, a light absorption layer, a hole transport layer, and a second electrode layer were formed in the same manner as in Example 1, sealed with cap glass, and a photoelectric conversion element (solar cell element) )

<Example 3>
When forming the electron transport layer, a photoelectric conversion element (solar cell element) was obtained in the same manner as in Example 2 except that the thermal ALD method (LabNano ^™ 9100 manufactured by Ensure Nanotech) was used as the atomic layer deposition method. Obtained.

<Comparative Example 1>
Place heat-resistant glass on the hot plate, place a glass substrate with indium tin oxide (ITO) film (0.7mm glass / 150nm ITO) (manufactured by Geomatech), and make contact with ITO (etched ITO) An aluminum plate was placed on the opposite side) and masked, and the substrate was heated to 450 ° C.

Next, an electron transport layer (thickness 20 nm) made of TiO ₂ was formed by spraying under the following conditions.
(Spray coating film formation conditions)
In a glow box, 28.4 mL of titanium tetraisopropoxide (Ti (OCH (CH ₃ ) ₂ ) ₄ ) is quickly put into a blue (brown) sample bottle with a stirrer chip and dried, and then 1 mL with stirring. 19.5-20 mL of acetylacetone was added at a time to prepare a spray solution.
The substrate was placed on a hot plate heated to 120 ° C., the spray liquid was sprayed twice while maintaining the distance between the substrate and the spray outlet to about 30 cm, and the substrate was rotated about 30 ° and allowed to stand for 20 seconds. This operation was continued until the spray liquid disappeared, and then cooled to room temperature.

  Next, on the electron transport layer, a light absorption layer, a hole transport layer, and a second electrode layer were formed in the same manner as in Example 1, sealed with cap glass, and a photoelectric conversion element (solar cell element) )

<Comparative example 2>
When the electron transport layer was formed, the same procedure as in Example 1 was repeated except that the film formation reaction was repeated 165 cycles at 45 ° C. by the plasma ALD method (Model OZONE, manufactured by For all, 60 W output of the plasma generator). Thus, a photoelectric conversion element (solar cell element) was obtained. The film thickness of the electron transport layer was 20 nm.

  Table 1 below collectively shows the film formation conditions of the electron transport layer and the refractive index at 589 nm in the solar cell elements of Examples 1 to 3 and Comparative Examples 1 and 2. It should be noted that the film formation conditions for the electron transport layer are appropriately adjusted according to the configuration, specifications, etc. of the ALD apparatus used. For example, when the film is formed by the plasma ALD method, the output value (W) of the plasma generator can be appropriately adjusted according to the ALD apparatus to be used.

  The photoelectric conversion efficiency (PCE) of the thus produced solar cell element was 12% in Example 1 and Example 2, and 6% in Example 3. On the other hand, the PCE of the solar cell element of Comparative Example 1 was less than 1%. In addition, in the solar cell element produced using the flexible translucent resin substrate as the translucent substrate in the same manner as the production conditions of Examples 1 to 3, it is possible to generate electricity with a PCE that significantly exceeds the comparative example. It has also been confirmed that.

From these results, it was confirmed that a solar cell element having high photoelectric conversion efficiency can be obtained when the refractive index at 589 nm is 1.80 or more in the electron transport layer made of amorphous TiO ₂ . That is, in the photoelectric conversion element of the present invention, the density of the electron transport layer is controlled and the surface flatness is excellent, so that the occurrence of leakage is suppressed, long-term stability is achieved, and high photoelectric conversion efficiency is achieved. It is considered that the element has. Thus, the correlation between the refractive index at a specific wavelength in the electron transport layer and the performance of the photoelectric conversion element is a novel finding found by the present inventors, and improves the performance of perovskite solar cells. Presents a new approach. Moreover, the photoelectric conversion element of this invention can make temperature conditions into 130 degrees C or less in all the manufacturing processes. Accordingly, it is expected that the perovskite solar cell using the roll-to-roll method can be made thinner, lighter and more flexible, and that it is possible to realize low cost and high productivity in terms of manufacturing technology.

Claims (5)

A photoelectric conversion device comprising a light-absorbing layer containing an organic ammonium metal halide or Cs metal halide, an electron transporting layer located beneath the light-absorbing layer comprises TiO ₂ amorphous, 589 nm of the electron transport layer A photoelectric conversion element having a refractive index of 1.80 or more.   The photoelectric conversion element according to claim 1, wherein the electron transport layer has a thickness of 5 to 100 nm.   The photoelectric conversion element according to claim 1, wherein the electron transport layer is an electron transport layer formed by laminating by an atomic layer deposition method.   The photoelectric conversion element according to claim 3, wherein the atomic layer deposition method is a plasma ALD method, an ozone ALD method, or a thermal ALD method. 5. The photoelectric conversion element according to claim 1, wherein the electron transport layer has a stacked structure including an amorphous TiO ₂ layer having a stack number of 50 to 2000. 6.

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