JP2017028027A - Solid-state junction photoelectric conversion element and p type semiconductor layer for solid-state junction photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state junction photoelectric conversion element in which power generation performance is enhanced, and to provide a P type semiconductor layer for solid-state junction photoelectric conversion element.SOLUTION: (1) In a solid-state junction photoelectric conversion element 10 where a base material, a first conductive layer, a light absorption layer 7 containing an organic inorganic perovskite compound, a P type semiconductor layer 5, and a second conductive layer 6 are provided in this order, the P type semiconductor layer contains a heterocyclic compound having pKa of less than 5.99. (2) A solid-state junction photoelectric conversion element described in (1), where the distance between all atoms composing the heterocyclic compound is 1.5 nm or less. (3) A solid-state junction photoelectric conversion element described in (1) or (2), where the P type semiconductor layer is formed of an organic semiconductor. (4) A P type semiconductor layer for solid-state junction photoelectric conversion element containing a heterocyclic compound having pKa of less than 5.99.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solid junction photoelectric conversion element and a P-type semiconductor layer for a solid junction photoelectric conversion element.

  Organic-inorganic hybrid perovskite compounds have attracted attention as sensitizers that can replace the dyes of dye-sensitized solar cells. A photoelectric conversion efficiency of 10.9% for a solid solar cell having no electrolyte solution, in which a P-type semiconductor layer of bifluorene type low molecular weight sprio-OMeTAD is formed on the surface of a crystal layer (perovskite compound layer) made of this perovskite compound Has been reported (see Non-Patent Document 1). Starting with this report, further improvements in photoelectric conversion efficiency have been reported one after another (see Non-Patent Document 2), and development for practical application is thriving.

“Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites” Science, 2012, 338, p643-. “Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells” Nature Materials 2014, 13, p897-.

For practical application, it is required to further improve the power generation performance of the solid junction photoelectric conversion elements described in Non-Patent Documents 1 and 2.
The present invention provides a solid junction photoelectric conversion element with improved power generation performance and a P-type semiconductor layer for a solid junction photoelectric conversion element.

[1] A solid junction photoelectric conversion element in which a substrate, a first conductive layer, a light absorption layer containing an organic / inorganic perovskite compound, a P-type semiconductor layer, and a second conductive layer are provided in this order. A solid junction photoelectric conversion element, wherein the P-type semiconductor layer includes a heterocyclic compound having a pKa of less than 5.99.
[2] The solid junction photoelectric conversion element according to [1], wherein the distance between all atoms constituting the heterocyclic compound is 1.5 nm or less.
[3] The solid junction photoelectric conversion element according to [1] or [2], wherein the P-type semiconductor layer is formed of an organic semiconductor.
[4] A P-type semiconductor layer for a solid junction photoelectric conversion element containing a heterocyclic compound having a pKa of less than 5.99.

The solid junction photoelectric conversion element of the present invention exhibits low internal resistance and high photoelectric conversion efficiency.
The P-type semiconductor layer for a solid junction photoelectric conversion element of the present invention contributes to the improvement of the power generation performance of the solid junction photoelectric conversion element.

It is a cross-sectional schematic diagram of the solid junction type photoelectric conversion element of 1st embodiment of this invention.

  Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments, but the present invention is not limited to such embodiments.

  In the present specification, “membrane” and “layer” are not distinguished unless otherwise specified. The solid junction photoelectric conversion element is sometimes referred to as a “solid solar cell”, and the organic / inorganic perovskite compound is simply referred to as a “perovskite compound”. Further, unless otherwise specified, the aggregate (bulk) of perovskite compounds is a crystalline compound.

<< Solid-junction photoelectric conversion element >>
A solid junction photoelectric conversion element according to the present invention includes a base material, a first conductive layer, an optional block layer, a light absorption layer containing an organic / inorganic perovskite compound, a P-type semiconductor layer, and a second conductive material. The layers are solid solar cells stacked in this order.

  As long as the relative order of the above layers is maintained, other layers may be inserted between any of the layers as long as the gist of the present invention is not impaired. For example, an arbitrary conductive layer may be inserted between the light absorption layer and the P-type semiconductor layer. Further, an arbitrary conductive layer may be inserted between the P-type semiconductor layer and the second conductive layer. From the viewpoint of reducing the internal resistance of the solid solar cell and increasing the photoelectric conversion efficiency, it is preferable that a P-type semiconductor layer is formed on the surface of the light absorption layer and a second conductive layer is formed on the surface of the P-type semiconductor layer. .

  As 1st embodiment of the solid solar cell concerning this invention, the solid solar cell 10 which has the laminated structure shown in FIG. 1 is mentioned, for example.

The solid solar cell 10 is laminated on the surface of the conductive layer 1 having the first conductive layer formed on the surface of the substrate, the block layer 2 laminated on the surface of the first conductive layer, and the surface of the block layer 2. The underlayer 3 containing the perovskite compound, the upper layer 4, the P-type semiconductor layer 5, and the counter electrode 6 made of the second conductive layer are sequentially laminated. In this laminated structure, the base layer 3 and the upper layer 4 are collectively referred to as a light absorption layer 7, the conductive substrate 1 and the block layer 2 are collectively referred to as a base 8, and the light absorption layer 7 and the base 8 are collectively referred to as a light. This is called electrode 9.
Hereinafter, each layer will be described in order.

<Conductive substrate 1>
The kind in particular of the electroconductive base material 1 which comprises the base | substrate 8 is not restrict | limited, For example, the electroconductive transparent base material used for the photoelectrode of the conventional solar cell is mentioned. Examples of the transparent substrate include a substrate made of glass or synthetic resin, a flexible film made of synthetic resin, and the like.

  When the material of the transparent substrate is a synthetic resin, examples of the synthetic resin include polyacrylic resin, polycarbonate resin, polyester resin, polyimide resin, polystyrene resin, polyvinyl chloride resin, and polyamide resin. Among these, polyester resins, particularly polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) are preferable from the viewpoint of manufacturing a thin, light and flexible solar cell.

  The surface of the transparent substrate is preferably coated with a metal oxide that constitutes the transparent conductive layer. By this coating, conductivity can be imparted to the surface without impairing the transparency of the transparent substrate. As the metal oxide, a compound used for a transparent conductive layer of a known solar cell can be applied. For example, tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide, tin oxide, antimony dope Examples thereof include tin oxide (ATO), indium oxide / zinc oxide (IZO), and gallium oxide / zinc oxide (GZO). The number of transparent conductive layers made of the metal oxide may be 1 or 2 or more.

The combination of the thickness and material of the conductive substrate 1 is not particularly limited, and examples thereof include a glass substrate having a thickness of 1 mm to 10 mm and a resin film having a thickness of 0.01 mm to 3 mm.
The thickness of the transparent conductive layer provided on the surface of the conductive substrate 1 is not particularly limited as long as desired conductivity can be obtained, and examples thereof include about 1 nm to 10 μm.

<Block layer 2>
Although the block layer 2 is not an essential configuration, the block layer 2 is preferably disposed between the conductive substrate 1 and the light absorption layer 7. When the block layer 2 is disposed, the conductive substrate 1 and the perovskite compound of the light absorption layer 7 are prevented from coming into direct contact. Thereby, the loss of electromotive force is prevented and the photoelectric conversion efficiency is improved.
The block layer 2 is preferably a non-porous dense layer, and more preferably a dense layer formed of an N-type semiconductor, in order to reliably prevent the contact.

The N-type semiconductor constituting the block layer 2 is not particularly limited, and examples thereof include oxide semiconductors excellent in electron conductivity such as ZnO, TiO ₂ , SnO, IGZO, SrTiO _{3 and the} like. Among these, TiO ₂ is particularly preferable because of its excellent electron conductivity.
There may be one kind of N-type semiconductor constituting the block layer 2 or two or more kinds.

The number of block layers 2 may be one, or two or more.
Although the total thickness of the block layer 2 is not specifically limited, For example, about 1 nm-1 micrometer are mentioned. When the thickness is 1 nm or more, the effect of preventing the loss is sufficiently obtained, and when the thickness is 1 μm or less, the internal resistance can be kept low.

<Light absorption layer 7>
The light absorption layer 7 is laminated on a base 8 composed of the conductive substrate 1 and the block layer 2. The light absorption layer 7 has a laminated structure in which an underlayer 3 containing a perovskite compound and an upper layer 4 made of a perovskite compound are formed on the surface of the underlayer 3 and formed of an N-type semiconductor or an insulator. Have. Here, the upper layer 4 is not an essential component, and the base layer 3 containing a perovskite compound may form the light absorption layer 7 alone.

The perovskite compound contained in the light absorption layer 7 is not particularly limited, and a perovskite compound used in a known solar cell is applicable, has a crystal structure, and is obtained by band gap excitation as in a typical compound semiconductor. Those showing light absorption are preferred. For example, CH ₃ NH ₃ PbI ₃ , which is a known perovskite compound, is known to have an extinction coefficient (cm ⁻¹ ) per unit thickness that is an order of magnitude higher than that of a sensitizing dye of a dye-sensitized solar cell. Yes.

<Underlayer 3>
The underlayer 3 is laminated on the substrate 8, that is, on the surface of the block layer 2. When the block layer 2 is not provided, the base layer 3 is laminated on the conductive surface of the conductive substrate 1.
A perovskite compound is supported (supported) on at least one of the inside and the surface of the underlayer 3.

The material of the underlayer 3 is preferably an N-type semiconductor and / or an insulator.
The underlayer 3 may be a porous film or a non-porous dense film, and is preferably a porous film. The perovskite compound is preferably supported by the porous structure of the underlayer 3. Even when the underlayer 3 is a dense film, the dense film preferably contains a perovskite compound. The dense film is preferably formed of an N-type semiconductor.

The kind of the N-type semiconductor is not particularly limited, and a known N-type semiconductor can be applied. Examples thereof include an oxide semiconductor that constitutes a photoelectrode of a conventional dye-sensitized solar cell. Specific examples include oxide semiconductors excellent in electronic conductivity such as titanium oxide (TiO ₂ ), zinc oxide (ZnO), tin oxide (SnO, SnO ₂ ), IGZO, strontium titanate (SrTiO ₃ ), and the like. . In some cases, a compound semiconductor such as Si, Cd, or ZnS doped with a pentavalent element may be used. Of these, titanium oxide is particularly preferable because of its excellent electron conductivity.
The N-type semiconductor forming the underlayer 3 may be one type or two or more types.

The type of the insulator is not particularly limited, and a known insulator can be used. For example, an oxide constituting an insulating layer of a conventional semiconductor device can be used. Specific examples include zirconium dioxide, silicon dioxide, aluminum oxide (AlO, Al ₂ O ₃ ), magnesium oxide (MgO), nickel oxide (NiO), and the like. Of these, aluminum (III) oxide (Al ₂ O ₃ ) is particularly preferable.
The insulator forming the underlayer 3 may be one type or two or more types.

  The amount of the perovskite compound contained in the underlayer 3 is not particularly limited, and is appropriately set so as to absorb an amount of light necessary for photoelectric conversion. Usually, the amount of light that can be absorbed increases as the content of the perovskite compound increases.

  The film structure of the underlayer 3 is preferably a porous film that can easily carry more perovskite compounds. As the amount of the perovskite compound contained in the underlayer 3 increases, the light absorption efficiency increases and the photoelectric conversion efficiency can be further improved.

The average pore diameter of the porous film constituting the underlayer 3 is preferably 1 nm to 100 nm or more, more preferably 5 nm to 80 nm, and still more preferably 10 nm to 50 nm.
When it is at least the lower limit of the above range, the perovskite compound is sufficiently supported in the pores.
The intensity | strength of a porous membrane is raised more as it is below the upper limit of the said range.
The average pore diameter can be measured by a known gas adsorption test or mercury intrusion test.

The thickness of the underlayer 3 is not particularly limited, and is preferably 10 nm to 10 μm, more preferably 50 nm to 1 μm, and still more preferably 100 nm to 0.5 μm, for example.
When it is at least the lower limit of the above range, a scaffold suitable for crystallization of the perovskite compound constituting the upper layer 4 is obtained. Furthermore, the light absorption efficiency in the underlayer 3 is increased, and more excellent photoelectric conversion efficiency is obtained.
If it is not more than the upper limit of the above range, the efficiency with which photoelectrons generated in the light absorption layer 7 reach the substrate 8 through the underlayer 3 is increased, and a more excellent photoelectric conversion efficiency is obtained.

<Upper layer 4>
The upper layer 4 laminated on the surface of the underlayer 3 is formed of a perovskite compound. When the perovskite compound is supported inside the underlayer 3, the upper layer 4 is not an essential component. When the upper layer 4 is laminated, the total amount of the perovskite compound contained in the light absorption layer 7 is increased, and the photoelectric conversion efficiency is further increased.

The thickness of the upper layer 4 is not specifically limited, For example, 1 nm-1 micrometer are preferable, 1 nm-500 nm are more preferable, 10 nm-500 nm are more preferable.
A photoelectric conversion efficiency can be improved more as it is more than the lower limit of the said range.
When the upper limit value is not more than the upper limit of the above range, the upper layer 4 is sufficiently adhered to the base layer 3 and the P-type semiconductor layer 5 and is prevented from peeling off.

<P-type semiconductor layer 5>
The P-type semiconductor layer 5 formed on the surface of the light absorption layer 7 is composed of a P-type semiconductor, and contains a heterocyclic compound (A) having a pKa of less than 5.99 as an additive.
When the P-type semiconductor layer 5 having holes (holes) is disposed on the surface of the light absorption layer 7, the generation of reverse current is suppressed, and the holes generated in the light absorption layer 7 due to light absorption are detected by the counter electrode 6. Can be easily transported to. Furthermore, the efficiency with which electrons move from the counter electrode 6 to the light absorption layer 7 is increased. As a result, the photoelectric conversion efficiency and voltage are increased. Furthermore, when the heterocyclic compound (A) is contained in the P-type semiconductor layer 5, the internal resistance is reduced and the photoelectric conversion efficiency is further improved. This heterocyclic compound (A) will be described in detail later.

The kind of the P-type semiconductor is not particularly limited, and may be an organic material or an inorganic material. For example, a P-type semiconductor for a hole transport layer of a known solar cell can be applied. Examples of the organic material include 2,2 ′, 7,7′-tetrakis (N, N-di-p-methoxyphenilamine) -9,9′-spirobifluorene (abbreviation: spiro-OMeTAD), Poly (3-hexylthiophene) (Abbreviation: P3HT), polytriarylamine (abbreviation: PTAA), and the like.
Examples of the inorganic material include copper compounds such as CuI, CuSCN, CuO, and Cu ₂ O, and nickel compounds such as NiO.
Among these materials, from the viewpoint of further improving the power generation performance, an organic semiconductor having high affinity with the heterocyclic compound (A) is preferable.

The thickness of the P-type semiconductor layer 5 is not specifically limited, For example, 1 nm-1000 nm are preferable, 5 nm-500 nm are more preferable, 30 nm-500 nm are more preferable.
When it is at least the lower limit of the above range, the contact between the light absorption layer 7 and the counter electrode 6 can be reliably prevented and the occurrence of leakage current can be prevented.
If it is not more than the upper limit of the above range, the internal resistance can be further reduced.

(Heterocyclic Compound (A))
In the solid solar cell 10, the power generation performance of the solid solar cell 10 is improved by including the heterocyclic compound (A) having a pKa of less than 5.99 inside the P-type semiconductor layer 5. Here, the pKa of t-butylpyridine is 5.99. Although t-butylpyridine may be contained in the P-type semiconductor layer 5, t-butylpyridine is contained in the P-type semiconductor layer 5 from the viewpoint of sufficiently obtaining the above effect by the heterocyclic compound (A). Preferably not.

  In an effort to improve the photoelectric conversion efficiency of the dye-sensitized solar cell, the present inventors have studied in the past that t-butylpyridine is contained in the electrolytic solution. When this study was developed and t-butylpyridine was added to the P-type semiconductor layer of the solid solar cell, the required power generation performance was not achieved. However, when a heterocyclic compound (A) having a pKa lower than that of t-butylpyridine was added to the P-type semiconductor layer using pKa as an index, it was found that the power generation performance was improved.

  Although the detailed mechanism by which the above effect is achieved is not yet elucidated, the base part of the heterocyclic compound (A) orders the atomic or molecular arrangement in the P-type semiconductor layer and promotes hole transport in the P-type semiconductor layer. I think that. As a result, it is assumed that the internal resistance of the solid solar cell is reduced and the photoelectric conversion efficiency is increased.

The heterocyclic compound (A) is a cyclic compound having a pKa of less than 5.99 and containing atoms (heteroatoms) other than carbon such as nitrogen, sulfur and oxygen in addition to carbon.
The ring structure of the heterocyclic compound (A) is not particularly limited, and may be monocyclic, polycyclic, or a 3- to 10-membered ring structure.
The hetero atom contained in the heterocyclic compound (A) is preferably a nitrogen atom.
The heterocyclic compound (A) is preferably a heteroaromatic compound, more preferably a nitrogen-containing aromatic compound, and further preferably a 5-membered or 6-membered nitrogen-containing aromatic compound. .

The pKa of the heterocyclic compound (A) can be determined by determining the equilibrium constant between the compound and the conjugate acid of the compound in an aqueous solution by ultraviolet-visible spectroscopy. The measurement temperature is 25 ° C. For more detailed methods, see "" Steric Effects in Displacement Reactions. III. The Base Strengths of Pyridine, 2,6-Lutidine and the Monoalkylpyridines "HERBERT C. BROWN AND XAVIER R. MIHM, J. Am. Chem. Soc. 1955 , Vol.77, pp1723-1726.
The above-mentioned pKa = 5.99 of t-butylpyridine is also a value obtained by the above method.
The pKa shown in this specification is “pKa1”.

  The pKa of the heterocyclic compound (A) is less than 5.99, preferably 0.00 or more and 5.90 or less, more preferably 1.00 or more and 5.00 or less, and 1.50 or more and 4.00 or less. Further preferred. Within the above range, the power generation performance can be further improved.

  The molecular diameter of the heterocyclic compound (A) is preferably 1.5 nm or less. A molecule of this size can be uniformly dispersed in the P-type semiconductor layer, and the power generation performance can be further improved. Here, if the distance between all atoms constituting the heterocyclic compound (A) is 1.5 nm or less, it can be said that the molecular diameter of the heterocyclic compound (A) is 1.5 nm or less.

  The distance between the atoms can be accurately obtained by calculating the distance between the centers of the atoms based on the atomic coordinates by the X-ray crystal structure analysis of the heterocyclic compound (A). However, for simplicity, the distance or molecular diameter can be determined using molecular model analysis software. For example, commercially available software such as trade name: MOPAC7 (published by James J. P. Stewart) can be applied.

As a suitable heterocyclic compound (A), the following can be illustrated, for example.
(Hereinafter, compound names: pKa: molecular diameter are described in this order.)
-3,5-dimethylpyrazole: pKa = 4.05: molecular diameter = 1.5 nm or less-2,5-dimethylpyrazine: pKa = 2.1: molecular diameter = 1.5 nm or less-1,2,4-triazole , PKa = 2.39, molecular diameter = 1.5 nm or less, pyrazole, pKa = 2.58, molecular diameter = 1.5 nm or less, 2,6-dimethylpyrazine, pKa = 2.5, molecular diameter = 1.5 nm・ Pyrazine, pKa = 0.6, molecular diameter = 1.5 nm or less

The content of the heterocyclic compound (A) in the P-type semiconductor layer 5 is estimated with respect to 100 parts by mass of the P-type semiconductor, assuming that the weight ratio of the mixed solution used for film formation is transferred directly into the film. 1-100 mass parts is preferable, 3-50 mass parts is more preferable, and 8-30 mass parts is further more preferable.
When it is at least the lower limit of the above range, hole transportation can be promoted and the power generation performance can be further improved.
If it is not more than the upper limit of the above range, the hole density (carrier density) can be prevented from decreasing, and the power generation performance can be further improved.

When the P-type semiconductor layer is formed of an organic semiconductor (semiconductor composed of an organic compound) that can be defined by the number of moles, the molar ratio represented by the organic semiconductor / heterocyclic compound (A) is 1/10 to 10 / 1 is preferable, 1/5 to 10/1 is more preferable, and 1/5 to 10/3 is more preferable.
When it is at least the lower limit of the above range, hole transportation can be promoted and the power generation performance can be further improved.
If it is not more than the upper limit of the above range, the hole density (carrier density) can be prevented from decreasing, and the power generation performance can be further improved.

<Counter electrode 6>
The second conductive layer laminated on the surface of the P-type semiconductor layer 5 constitutes the counter electrode 6.
The material of the second conductive layer is not particularly limited, and for example, any one or more metals selected from the group consisting of gold, silver, copper, aluminum, tungsten, nickel, and chromium are suitable.
The thickness of the counter electrode 6 which consists of a 2nd conductive layer is not specifically limited, For example, 10-100 nm is preferable.

<< Power generation of solid solar cell 10 >>
In the solid solar cell 10, the light absorption layer 7 contains a perovskite compound. When the crystal of the perovskite compound absorbs light, photoelectrons and holes are generated in the crystal. Photoelectrons are received by the underlayer 3 or the block layer 2 and move to the working electrode (positive electrode) formed by the conductive substrate 1. Holes move to the counter electrode (negative electrode) formed by the second conductive layer via the P-type semiconductor layer 5.
The current generated by the solid solar cell 10 is taken out to an external circuit through an extraction electrode connected to the positive electrode and the negative electrode.

<< Method for Manufacturing Solid Solar Cell >>
In the first embodiment of the method for producing a solid solar cell according to the present invention, a P-type semiconductor and a heterocyclic compound (A) having a pKa of less than 5.99 are formed on a light absorption layer 7 containing a perovskite compound. It is a manufacturing method of the solid solar cell 10 illustrated in FIG. 1 which has the process of forming the P-type semiconductor layer 5 containing a P-type semiconductor and a heterocyclic compound (A) by apply | coating the solution containing and drying. .
Hereinafter, the formation method of each layer is demonstrated in order.

<Preparation of conductive substrate 1>
The conductive substrate 1 can be produced by a conventional method, and a commercially available product may be used.

<Formation of block layer 2>
The formation method of the block layer 2 is not specifically limited, The well-known method which can form the dense layer which consists of N type semiconductor by desired thickness on the surface of the transparent conductive layer of the electroconductive base material 1 is applicable. Examples thereof include a sputtering method, a vapor deposition method, and a sol-gel method in which a dispersion liquid containing an N-type semiconductor precursor is applied.

Examples of N-type semiconductor precursors include titanium tetrachloride (TiCl ₄ ), peroxotitanic acid (PTA), titanium alkoxide such as titanium ethoxide and titanium isopropoxide (TTIP), zinc alkoxide, alkoxysilane, and zirconium. Examples thereof include metal alkoxides such as alkoxides.

<Formation of underlayer 3>
The method for forming the underlayer 3 is not particularly limited, and for example, a method for forming a semiconductor layer carrying a sensitizing dye of a conventional dye-sensitized solar cell can be applied.

  As a specific example, for example, a porous base layer 3 made of fine particles is prepared by applying a paste containing fine particles made of an N-type semiconductor or insulator and a binder to the surface of the substrate 8 by a doctor blade method, drying, and firing. Can be formed. Further, by spraying fine particles onto the substrate 8, a porous or non-porous underlayer 3 made of the fine particles can be formed.

  The method for spraying the fine particles is not particularly limited, and a known method can be applied, for example, an aerosol deposition method (AD method), an electrostatic fine particle coating method (electrostatic spray method) in which fine particles are accelerated by electrostatic force, The cold spray method etc. are mentioned. Among these methods, the AD method is preferable because the speed of the fine particles to be sprayed can be easily adjusted and the film quality and thickness of the underlying layer 3 to be formed can be easily adjusted.

  The AD method is a method in which fine particles are accelerated to a subsonic to supersonic speed by a carrier gas such as nitrogen and sprayed onto a substrate to form a film made of fine particles on the substrate surface. The fine particles that have been sprayed collide with the fine particles that have been bonded to the surface of the substrate, thereby forming a film in which the fine particles are bonded. In the collision between the fine particles, a temperature rise that causes the fine particles to melt hardly occurs. Moreover, since the formed porous film has sufficient strength and electronic conductivity as an electrode of a solar cell, a baking step after film formation is not essential. However, you may perform baking (sintering) as needed.

  Since the AD method can form the underlayer 3 at room temperature, a synthetic resin film or the like having a glass transition temperature of less than 200 ° C. can be applied as a substrate. Therefore, since various types of base materials can be used as compared with a method requiring a high-temperature firing process, it is possible to manufacture various types of solid solar cells according to a wide range of purposes and applications.

  By appropriately adjusting the speed of the fine particles to be sprayed, the film forming rate and the porosity of the film can be adjusted. Usually, the higher the spray rate, the higher the film-forming rate and the lower the membrane porosity. Accordingly, when the underlayer 3 is formed, the underlayer 3 can be formed by arbitrarily selecting the film structure of the porous film or the dense film by adjusting the spraying speed of the fine particles.

  As a material for forming the underlayer 3, one or more types of N-type semiconductor fine particles and one or more types of insulating fine particles may be used in combination.

The average particle diameter r of the fine particles is preferably 1 nm ≦ r <200 nm, more preferably 10 nm ≦ r ≦ 70 nm, and further preferably 10 nm ≦ r ≦ 30 nm.
The larger the value is above the lower limit of the above range, the easier it is to insert the perovskite compound sufficiently into the pores constituting the porous structure of the underlayer 3. The smaller the value is below the upper limit of the above range, the more the interface between the perovskite compound and the N-type semiconductor fine particles increases, the photoelectrons can be easily taken out, and the underlying layer 3 and the P-type semiconductor layer 5 come into contact with each other to thereby lose the electromotive force. Can be prevented.

  The average particle diameter r of the fine particles can be obtained as an average value of particle diameters measured by observing a plurality of fine particles with an electron microscope. In this case, the larger the number of fine particles to be measured, the better. For example, 10 to 50 particles may be measured and the arithmetic average thereof may be obtained. Or it can also determine as a peak value of the particle diameter (volume average diameter) distribution obtained by the measurement of the laser diffraction type particle size distribution measuring apparatus. If the measurement sample of the same fine particles is measured by the above two methods and the measured values are different from each other, whether or not they are included in the above average particle diameter range based on the values obtained by observation with an electron microscope. judge.

  The method for incorporating the perovskite compound in the underlayer 3 is not particularly limited. For example, a method in which the formed underlayer 3 is impregnated with a solution containing the perovskite compound or a precursor thereof, or a material to which the perovskite compound is previously attached is used. And a method of forming the base layer 3. The above two methods may be used in combination.

  When the underlayer 3 is formed by a spraying method such as the AD method, the underlayer 3 containing the perovskite compound inside is formed by spraying fine particles of an N-type semiconductor or insulator, to which the perovskite compound is adhered, onto the surface of the substrate 8. Can be formed.

  As a method for attaching the perovskite compound to the fine particles, a raw material to which the perovskite compound crystallized is adhered by immersing the fine particles in a raw material solution in which a perovskite compound or a precursor of the perovskite compound is dissolved and further drying the solvent. The method of obtaining particle | grains is mentioned.

<Formation of the light absorption layer 7>
When the base layer 3 is formed, if a material to which a perovskite compound is previously attached is used, the light absorption layer 7 composed of the base layer 3 containing the perovskite compound is obtained. By further inserting or laminating a perovskite compound inside or on the surface of the underlayer 3, a light absorbing layer 7 containing a larger amount of perovskite compound is obtained.
On the other hand, when the underlayer 3 not containing the perovskite compound is formed, a light absorbing layer 7 containing a sufficient amount of the perovskite compound is obtained by inserting or laminating the perovskite compound inside and on the surface of the underlayer 3. It is done.

  The method of inserting the perovskite compound into the underlayer 3 and forming the upper layer 4 made of the perovskite compound on the surface of the underlayer 3 is not particularly limited, and examples thereof include the following methods. That is, a raw material solution in which a perovskite compound or a perovskite compound precursor is dissolved is applied to the surface of the underlayer 3 and impregnated inside, and the solvent is dried in a state where a solution layer made of a solution having a desired thickness is present on the surface It is a method to do.

  At least a part of the raw material solution applied to the underlayer 3 penetrates into the porous film of the underlayer 3, and crystallization proceeds with the drying of the solvent, and the perovskite compound adheres and deposits in the porous film. Further, by applying a sufficient amount of the raw material solution, the raw material solution that has not penetrated into the porous film forms an upper layer 4 made of a perovskite compound on the surface of the underlayer 3 together with the drying of the solvent. The perovskite compound constituting the upper layer 4 and the perovskite compound in the underlayer 3 are integrally formed, and the light absorption layer 7 is integrally formed.

  The reaction for generating the perovskite compound from the precursor can take place at room temperature, but may be heated to promote this reaction. Moreover, you may anneal a perovskite compound at about 40-150 degreeC from a viewpoint of improving photoelectric conversion efficiency. Furthermore, you may heat or sinter at the temperature exceeding 150 degreeC as needed.

The perovskite compound used in the present embodiment is not particularly limited as long as it can generate an electromotive force by light absorption, and a known perovskite compound is applicable. Among these, perovskite-type crystals can be formed, and the following composition formula (1) having an organic component and an inorganic component in a single compound:
ABX ₃ (1)
The perovskite compound represented by these is preferable.

  In the composition formula (1), A represents an organic cation, B represents a metal cation, and X represents a halogen ion. In the perovskite crystal structure, the B site can take octahedral coordination with the X site. It is considered that the metal cation at the B site and the atomic orbital of the halogen ion at the X site are mixed to form a valence band and a conduction band related to photoelectric conversion.

The metal constituting the metal cation represented by B in the composition formula (1) is not particularly limited, and examples thereof include Cu, Ni, Mn, Fe, Co, Pd, Ge, Sn, Pb, and Eu. Among these, Pb and Sn are preferable because they can easily form a highly conductive band by hybridization with the atomic orbitals of halogen ions at the X site.
The metal cation constituting the B site may be one type or two or more types.

The halogen constituting the halogen ion represented by X in the composition formula (1) is not particularly limited, and examples thereof include F, Cl, Br, and I. Among these, Cl, Br, and I are preferable because they can easily form a highly conductive band by a hybrid orbital with a metal cation at the B site.
There may be one kind of halogen ion constituting the X site, or two or more kinds.

The organic group constituting the organic cation represented by A in the composition formula (1) is not particularly limited, and examples thereof include alkylammonium derivatives and formamidinium derivatives.
The organic cation constituting the A site may be one type or two or more types.

  Examples of the organic cation formed by the alkyl ammonium derivative include carbon such as methyl ammonium, dimethyl ammonium, trimethyl ammonium, ethyl ammonium, propyl ammonium, isopropyl ammonium, tert-butyl ammonium, pentyl ammonium, hexyl ammonium, octyl ammonium, and phenyl ammonium. Examples include primary or secondary ammonium having an alkyl group of 1 to 6. Of these, methylammonium, which can easily obtain perovskite crystals, is preferred.

  Examples of the organic cation formed by the formamidinium derivative include formamidinium, methylformamidinium, dimethylformamidinium, trimethylformamidinium, and tetramethylformamidinium. Of these, formamidinium is preferred because it can easily obtain a perovskite crystal.

As a suitable perovskite compound represented by the composition formula (1), for example, CH ₃ NH ₃ PbI ₃ , CH ₃ NH ₃ PbI _3-h Cl _h (h represents 0 to ₃ ), CH ₃ NH ₃ PbI _{The following} composition formula (2) such as _3-j Br _j (j represents 0 to 3):
RNH ₃ PbX ₃ (2)
The alkylamino lead halide represented by these is mentioned. In the composition formula (2), R represents an alkyl group, and X represents a halogen ion. Since the perovskite compound having this composition formula has a wide absorption wavelength range and can absorb a wide wavelength range of sunlight, excellent photoelectric conversion efficiency can be obtained.

  The alkyl group represented by R in the composition formula (2) is preferably a linear, branched or cyclic saturated or unsaturated alkyl group having 1 to 6 carbon atoms. It is more preferably a chain saturated alkyl group, and further preferably a methyl group, an ethyl group, or an n-propyl group. With these preferable alkyl groups, perovskite crystals can be easily obtained.

In the formation of the light absorption layer 7, examples of the precursor contained in the raw material solution include a halide (BX) containing the metal ions at the B site and the halogen ions at the X site, and the A site described above. A halide (AX) containing an organic cation and a halogen ion at the X site.
A single raw material solution containing halide (AX) and halide (BX) may be applied to the underlayer 3, or two raw material solutions each containing halide individually may be applied in turn to the underlayer 3. You may apply to.

  The solvent of the raw material solution is not particularly limited as long as it dissolves the raw material and does not impair the underlayer 3. For example, ester, ketone, ether, alcohol, glycol ether, amide, nitrile, carbonate, halogenated hydrocarbon , Hydrocarbons, sulfones, sulfoxides, formamides and the like.

  As an example, a halogenated alkylamine and a lead halide are dissolved in a mixed solvent of γ-butyrolactone (GBL) and dimethyl sulfoxide (DMSO), and the solution is applied to the underlayer 3 and dried, whereby the composition formula (2 A perovskite crystal composed of a perovskite compound represented by Furthermore, as described in Non-Patent Document 2, after applying a solvent miscible with GBL or DMSO, such as toluene or chloroform, on the perovskite crystal, annealing is performed at about 100 ° C. You may add the process to do. This additional treatment may improve crystal stability and increase photoelectric conversion efficiency.

  The concentration of the raw material in the raw material solution is not particularly limited, and is preferably a concentration that is sufficiently dissolved and exhibits a viscosity that allows the raw material solution to penetrate into the porous membrane.

  The amount of the raw material solution applied to the underlayer 3 is not particularly limited. For example, the raw material solution penetrates all or at least a part of the porous film and has an upper layer having a thickness of about 1 nm to 1 μm on the surface of the porous film. A coating amount such that 4 is formed is preferable.

The method for applying the raw material solution to the underlayer 3 is not particularly limited, and known methods such as a gravure coating method, a bar coating method, a printing method, a spray method, a spin coating method, a dip method, and a die coating method can be applied.
Application | coating of the said raw material solution with respect to the base layer 3 may be completed by 1 time, and you may repeat application | coating after the 2nd time after drying. The application amount after the second time may be the same as or different from the first application amount.

The method for drying the raw material solution applied to the underlayer 3 is not particularly limited, and known methods such as natural drying, reduced pressure drying, and hot air drying can be applied.
The drying temperature of the raw material solution applied to the underlayer 3 may be a temperature at which the crystallization of the perovskite compound proceeds sufficiently, and examples include a range of 40 to 150 ° C.

<Formation of P-type semiconductor layer 5>
The method for forming the P-type semiconductor layer 5 is not particularly limited. For example, a solution in which the P-type semiconductor and the heterocyclic compound (A) are dissolved or dispersed in a solvent in which the perovskite compound constituting the light absorption layer 7 is difficult to dissolve. A method of obtaining the P-type semiconductor layer 5 by preparing, applying this solution to the surface of the light absorption layer 7 and drying it is mentioned.

The concentration of the P-type semiconductor and the heterocyclic compound (A) in the solution is not particularly limited, and is appropriately determined depending on the content ratio of the P-type semiconductor and the heterocyclic compound (A) in the P-type semiconductor layer 5 to be formed. Adjust it.
The amount of the solution applied to the light absorption layer 7 is not particularly limited, and the amount of application may be adjusted as appropriate according to the thickness of the P-type semiconductor layer 5 to be formed.
The method of applying the solution to the light absorbing layer 7 and the method of drying are not particularly limited, and examples thereof include the same method as the method of applying the perovskite compound raw material solution to the underlayer 3 and drying.

<Formation of counter electrode 6>
The method for forming the counter electrode 6 made of the second conductive layer on the surface of the P-type semiconductor layer 5 is not particularly limited. For example, a known method such as sputtering or vapor deposition for forming a counter electrode of a conventional solar cell is used. A film forming method can be applied.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited by these examples.

[Example 1]
A conductive glass substrate having an FTO film made of fluorine-doped SnO ₂ formed on the surface of the glass substrate was used. A solution of titanium diisopropoxide bis (acetylacetonate) dissolved in isopropanol (manufactured by Sigma-Aldrich) was sprayed on the surface of the FTO film by a known spray pyrolysis method to form a block layer made of titania having a thickness of 30 nm. Formed.

A raw material solution of N, N-dimethylformamide (DMF) containing 0.9 M concentration of lead iodide (PbI ₂ ) and 0.4 M concentration of methylammonium iodide (CH ₃ NH ₃ I) was prepared. In this raw material solution, anatase-type TiO ₂ particles having an average particle diameter of about 15 nm (manufactured by Nippon Aerosil Co., Ltd .; trade name: P15) were immersed, stirred gently for 15 minutes, and then taken out and dried to obtain a composition formula ( Raw material fine particles in which perovskite crystals of an organic-inorganic hybrid composed of a perovskite compound represented by CH ₃ NH ₃ PbI ₃ ) adhered to the surface were obtained.

  By the aerosol deposition method (AD method), the above-mentioned raw material fine particles were sprayed on the surface of the block layer to form a porous light absorption layer having a thickness of 300 nm made of titania fine particles with perovskite crystals adhering to the surface in one minute. .

  Contains 6.9 wt% (100 parts by mass) spiro-OMeTAD as an organic semiconductor and 0.71 wt% (10.2 parts by mass) 3,5-dimethylpyrazole (3,5-DMPzo) as an additive A chlorobenzene solution was applied to the surface of the light absorption layer by a spin coating method to form a P-type semiconductor layer having a thickness of 200 nm composed of spiro-OMeTAD and 3,5-DMPzo.

  A counter electrode having a thickness of 50 nm made of gold (Au) was formed on the surface of the P-type semiconductor layer by a known vapor deposition method.

  The structure shown in FIG. 1 in which the conductive substrate 1 / blocking layer 2 / light-absorbing layer 7 / P-type semiconductor layer 5 / counter electrode 6 comprising the conductive substrate 1 / block layer 2 / underlayer 3 are laminated in this order (except the upper layer 4). ) Was obtained.

[Examples 2 to 9, Comparative Examples 1 to 4]
A solid solar cell was produced in the same manner as in Example 1 except that the type, concentration, and type of P-type semiconductor were changed as shown in Table 1.

The compound names and structural formulas of the additives listed in the table are as follows.
3,5-DMPzo: 3,5-dimethylpyrazole
2,5-DMPzi: 2,5-dimethylpyrazine
tBP: t-butylpyridine
1,2,4-Taz: 1,2,4-triazole

  In order to evaluate the current-voltage characteristics of the produced solar cell, the internal resistance and photoelectric conversion efficiency were measured using a solar simulator (AM1.5). The results are shown in Table 2.

  From the above results, the solar cell of the example provided with the P-type semiconductor layer containing an additive having a pKa of less than 5.99 has an internal resistance as compared with the comparative example to which tBP (pKa = 5.99) is added. It is clear that the photoelectric conversion efficiency was improved.

  The configurations and combinations thereof in the embodiments described above are examples, and the addition, omission, replacement, and other modifications of the configurations can be made without departing from the spirit of the present invention. Further, the present invention is not limited by each embodiment, and is limited only by the scope of the claims.

DESCRIPTION OF SYMBOLS 1 ... Conductive base material, 2 ... Block layer, 3 ... Underlayer, 4 ... Upper layer, 5 ... P-type semiconductor layer, 6 ... Counter electrode (2nd conductive layer), 7 ... Light absorption layer, 8 ... Base | substrate, 9 ... Photoelectrode, 10 ... Solid junction photoelectric conversion element (solid solar cell)

Claims (4)

A substrate, a first conductive layer, a light absorption layer containing an organic / inorganic perovskite compound, a P-type semiconductor layer, and a second conductive layer are solid junction photoelectric conversion elements provided in this order,
A solid junction photoelectric conversion element, wherein the P-type semiconductor layer includes a heterocyclic compound having a pKa of less than 5.99.   The solid junction photoelectric conversion element according to claim 1, wherein the distance between all atoms constituting the heterocyclic compound is 1.5 nm or less.   The solid junction photoelectric conversion element according to claim 1 or 2, wherein the P-type semiconductor layer is formed of an organic semiconductor.   A P-type semiconductor layer for a solid junction photoelectric conversion element, comprising a heterocyclic compound having a pKa of less than 5.99.

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