JP6857868B2 - Light absorbing material and solar cells using it - Google Patents

Description

The present disclosure relates to a light absorbing material and a solar cell using the same.

In recent years, _{perovskite-type crystals represented by ABX 3} (A is a monovalent cation, B is a divalent cation, and X is a halogen anion) and similar structures thereof (hereinafter referred to as "perovskite-type compounds") have been exposed to light. Research and development of perovskite solar cells used as an absorbent material is underway.

Non-Patent Document 1 discloses that a perovskite-type compound represented by _{CH 3} NH ₃ PbI ₃ (hereinafter, _{may be abbreviated as "MAPbI 3} ") is used as a light absorbing material for a perovskite solar cell. .. Further, a perovskite-type compound represented by (NH ₂ ) ₂ CHPbI ₃ (hereinafter, _{may be abbreviated as “FAPbI 3”) is also disclosed.}

Jeong-Hyeek Im, 4 others, "Nature Nanotechnology" (USA), November 2014, Volume 9, p. 927-932

It is required to further improve the conversion efficiency of perovskite solar cells.

An exemplary, but not limited, embodiment of the present disclosure provides a light absorbing material capable of increasing the conversion efficiency of a perovskite solar cell. Further, a solar cell using such a light absorbing material is provided.

One embodiment of the present disclosure has a perovskite-type crystal structure _{represented by ABX 3 , in which (NH 2} ) ₂ CH ⁺ is arranged at the A ^{site, Pb 2+} is arranged at the B site, and I ^{− is arranged at the X site.} It contains a light absorbing material mainly containing a compound in which the element ratio of I to Pb in the composition analysis by X-ray photoelectron spectroscopy is 1.8 or more and 2.7 or less.

According to one embodiment of the present disclosure, there is provided a light absorbing material capable of increasing the conversion efficiency of a perovskite solar cell. Further, a solar cell using such a light absorbing material is provided.

It is a figure which shows the relationship between the fluorescence lifetime and conversion efficiency in a perovskite solar cell. It is a schematic process sectional view for demonstrating an example of the manufacturing method of the perovskite type compound in this disclosure. It is a schematic process sectional view for demonstrating an example of the manufacturing method of the perovskite type compound in this disclosure. It is a schematic process sectional view for demonstrating an example of the manufacturing method of the perovskite type compound in this disclosure. It is an enlarged photograph which shows an example of the perovskite type compound in this disclosure. It is an enlarged photograph which shows another example of the perovskite type compound in this disclosure. It is a figure which shows the XPS spectrum of the perovskite type compound of Example 2 and Comparative Example 2, and shows the spectrum near the binding energy corresponding to C1s. It is a figure which shows the XPS spectrum of the perovskite type compound of Example 2 and Comparative Example 2, and shows the spectrum near the binding energy corresponding to N1s. It is a figure which shows the XPS spectrum of the perovskite type compound of Example 2 and Comparative Example 2, and shows the spectrum near the binding energy corresponding to Pb4f. It is a figure which shows the XPS spectrum of the perovskite type compound of Example 2 and Comparative Example 2, and shows the spectrum near the binding energy corresponding to I3d5. It is a figure which shows the X-ray diffraction pattern of the perovskite type compound of Example 1. It is a figure which shows the X-ray diffraction pattern of the perovskite type compound of the comparative example 1. FIG. It is a figure which shows the fluorescence spectrum of the perovskite type compound of Example 1 and Comparative Example 1. It is a figure which shows the fluorescence attenuation curve of the perovskite type compound of Example 1 and Comparative Example 1. It is a figure which shows the absorption spectrum of the perovskite type compound of Example 1 and Comparative Example 1. It is a schematic cross-sectional view which shows an example of the solar cell by this disclosure. FIG. 5 is a schematic cross-sectional view showing another example of the solar cell according to the present disclosure. FIG. 5 is a schematic cross-sectional view showing still another example of the solar cell according to the present disclosure. FIG. 5 is a schematic cross-sectional view showing still another example of the solar cell according to the present disclosure. It is a figure which shows the XRD pattern of the compound of Example 1 and Comparative Example 1. It is a figure which shows the XRD pattern of the compound of Example 1 and Comparative Example 1. It is a figure which shows the IPCE efficiency measurement result of the solar cell of Example 11 and Comparative Example 4.

(Embodiment)
The findings on which the present invention is based are as follows.

It is known that the performance as a light absorbing material for a solar cell is determined by its band gap. For details, see William Shockley, and one other person, "Journal of Applied Physics" (USA), March 1961, Vol. 32, No. 3, p. It is described in 510-519. This conversion efficiency limit is known as the Shockley-Queisserlimit limit, and the theoretical efficiency is maximized when the bandgap is 1.4 eV. When the band gap is larger than 1.4 eV, a high voltage can be obtained, but the current value becomes small due to the shortened wavelength of light absorption. On the contrary, when it is smaller than 1.4 eV, the current value increases due to the lengthening of the wavelength of light absorption, but the open circuit voltage becomes small.

However, the bandgap of conventional perovskite-type compounds is far from the maximum theoretical efficiency of 1.4 eV. For example, the bandgap of the above-mentioned MAPbI ₃ perovskite type compound is 1.59 eV, and the bandgap of the FAPbI ₃ perovskite type compound is 1.49 eV. Therefore, there is a demand for a perovskite-type compound having a bandgap closer to 1.4 eV or 1.4 eV. When such a perovskite-type compound is used as a light absorbing material for a solar cell, it becomes possible to realize a solar cell having a higher conversion efficiency than the conventional one.

FAPbI ₃ generally has a trigonal structure. Giles E Eperon, 5 others, "Energy & Environmental Science" (UK), 2014, Vol. 7, No. 3, p. As reported in 982-988, the _{bandgap of FAPbI 3} is, for example, 1.48 eV. In FAPbI ₃ , in the perovskite-type crystal structure represented by _{ABX 3} , the A site is occupied by ^{FA +} (formamidinium cation), the B site ^{is occupied by Pb 2+} , and the X site ^{is occupied by I −.} Some of the X sites bromine - also be substituted with such ^(Br).

Also, for example, Shopping Pang, 9 others, "Chemistry of Materials" (USA), January 2014, Vol. 26, p. On pages 1487 to 1488 of 1485-1491, it is explained that _{the crystal of FAPbI 3} ^{having FA +} cannot have a cubic structure, and the proximity structure of ^{FA + is distorted.}

In addition, Marina R.M. Filip, 3 others, "Nature Communications" (USA), December 2014, Volume 5, 5757, show systematic calculation results for perovskite-type compounds in which the A site in _{FAPbI 3 is replaced with various cations.} ing. They focused on the angle bond angle between PbI ₆ octahedra, PbI ₆ is ideally positioned, that is, a narrow band gap as arranged without distortion obtained, as contrary to PbI ₆ octahedra are arranged in a zigzag , Reports that a wide bandgap can be obtained. It has also been shown that FAPbI ₃ has a somewhat distorted structure and is not a completely symmetrical structure.

The above Marina R.M. As reported by Filip et al. And Shipping Pang et al., FAPbI ₃ basically has a trigonal structure, and its PbI ₆ octahedral structure has strain. The strain of the PbI _{6 octahedral structure is considered to be a factor in which FAPbI 3} shows a wide bandgap of about 1.49 eV.

In view of these considerations, the present inventor _{has found a novel FAPbI 3} perovskite-type compound in which _{the strain between PbI 6} octahedrons is small and the bandgap is narrower than before, as a result of repeated studies.

The outline of one embodiment of the present disclosure is as follows.

Light-absorbing material in an embodiment of the present disclosure includes a perovskite-type crystal structure represented by ABX _3, in the A site ^{_{(NH 2) 2 CH +,}} Pb 2+ at the B site, I to X site ^- position However, it mainly contains compounds in which the element ratio of I to Pb in the composition analysis by X-ray photoelectron spectroscopy is 1.8 or more and 2.7 or less.

The element ratio of I to Pb in the composition analysis by X-ray photoelectron spectroscopy may be 2.1 or more and 2.7 or less.

Light-absorbing material in other embodiments of the present disclosure includes a perovskite-type crystal structure represented by ABX _3, in the A site ^{_{(NH 2) 2 CH +,}} Pb 2+ at the B site, the X site I ^- is It mainly contains a compound that is located and has an elemental ratio of I to Pb of less than 3, which has a peak in the fluorescence spectrum at 880 nm or more and 905 nm or less.

Light-absorbing material in still another embodiment of the present disclosure includes a perovskite-type crystal structure represented by ABX _3, in the A site ^{_{(NH 2) 2 CH +,}} Pb 2+ at the B site, the X site I ^- The X-ray diffraction pattern of the compound mainly contains a compound in which the element ratio of I to Pb is less than 3, and the X-ray diffraction pattern of the compound is the first peak located at 13.9 ° ≤ 2θ ≤ 14.1 ° and 23. It has a second peak located at 5 ° ≤ 2θ ≤ 24.5 ° and a third peak located at 27 ° ≤ 2θ ≤ 29 °, and the intensity of the second peak is the intensity of the first peak. It is 40% or less, and the intensity of the third peak is larger than the intensity of the first peak.

In certain embodiments, the X-ray diffraction pattern of the compound may further have a fourth peak located at 19.65 ° ≤ 2θ ≤ 19.71 °.

In certain embodiments, the X-ray diffraction pattern of the compound may further have a fifth peak located at 39.98 ° ≤ 2θ ≤ 40.10 °.

Light-absorbing material in still another embodiment of the present disclosure includes a perovskite-type crystal structure represented by ABX _3, in the A site ^{_{(NH 2) 2 CH +,}} Pb 2+ at the B site, the X site I ^- Is located and mainly contains compounds in which the element ratio of I to Pb in the composition analysis by Rutherford backscattering spectroscopy is 2.9 or less.

The solar cell of one embodiment of the present disclosure is located on a first electrode having conductivity, a light absorption layer that is located on the first electrode and converts incident light into electric charges, and a light absorption layer. The light absorbing layer includes any of the above light absorbing materials, including a second electrode having conductivity.

(Composition and crystal structure of perovskite-type compound)
<Composition>
The light absorbing material of one embodiment of the present disclosure has a perovskite-type crystal structure _{represented by ABX 3 , in which (NH 2} ) ₂ CH ⁺ is arranged at the A site, Pb ^{2+ is arranged at the B site, and I −} is arranged at the X site. Mainly contains perovskite-type compounds. The elemental ratio of I to Pb in the perovskite compound is less than 3. In other words, if the element ratio of Pb is 1 and the element ratio of I is 3 × (1-x), x> 0. In the present specification, this value of x is referred to as an iodine deficiency rate with respect to Pb (hereinafter, abbreviated as "iodine deficiency rate").

The iodine deficiency rate x can be determined by analyzing the composition of the perovskite-type compound. For example, the content ratio of each element may be obtained by composition analysis, and the iodine deficiency rate x may be calculated from the content ratio of I to Pb. As the composition analysis, XPS (X-ray photoelectron spectroscopy) measurement, RBS (Rutherford backscattering spectroscopy), NRA (nuclear reaction analysis) and the like may be performed. The analysis result (ratio of elements) may differ depending on the composition analysis method. This is because the sensitivity ratio may differ depending on the composition analysis method depending on the sample measurement area, measurement depth, and elemental state of the analysis. As an example, in the composition analysis by XPS measurement, the element ratio of I to Pb 3 × (1-x) is, for example, 1.8 or more and 2.7 or less, and the iodine deficiency rate x is, for example, 0.1 or more and 0.4 or less. Is.

The light absorbing material of the present embodiment may mainly contain the above-mentioned perovskite-type compound and may contain impurities. The proportion of the perovskite-type compound in the light absorbing material may be, for example, 90 wt% or more. The light absorbing material of the present embodiment may further contain another compound different from the above-mentioned perovskite type compound.

Next, an example of the analysis result of the perovskite type compound of the present disclosure will be described.

<X-ray diffraction pattern>
The X-ray diffraction (XRD) pattern of the perovskite-type compound in the present embodiment using CuKα rays as X-rays is, for example, 13.9 to 14.1 °, 19 to 21 °, 23.5 to 24.5 °. , 27-29 °, 30.5-32.5 °, 33.5-35.5 °, 39-41 °. If the light absorbing material of the present disclosure is not a mixture, these peaks will appear as a single peak and there will be no multiple peaks within the above range. Further, when it is not a mixture, there is no peak other than the above at a diffraction angle of 40 ° or less.

In the present specification, among the above-mentioned X-ray diffraction pattern peaks, the peak located at 13.9 ° ≤ 2θ ≤ 14.1 ° is located at the "first peak", 23.5 ° ≤ 2θ ≤ 24.5 °. The peak that forms the peak is called the “second peak”, and the peak located at 27 ° ≦ 2θ ≦ 29 ° is called the “third peak”. The first peak is assigned to the (100) plane, the second peak is assigned to the (111) plane, and the third peak is assigned to the (200) plane. Further, the peaks located at 19 to 21 ° and attributed to the (110) plane are referred to as "fourth peak", and the peaks located at 39 to 41 ° and attributed to the (220) plane are referred to as "fifth peak". Call. The fourth peak may be located, for example, 19.65 ° ≤ 2θ ≤ 19.71 °, and the fifth peak may be located, for example, 39.98 ° ≤ 2θ ≤ 40.10 °.

The X-ray diffraction pattern of the perovskite-type compound in the present embodiment is different from the _{conventional FAPbI 3 in the following points. First, the intensity ratio I (111)} / I ₍₁₀₀₎ of the second peak to the first peak is, for example, more than 0% and 40% or less, and the intensity ratio of the _{conventional FAPbI 3 is I (111)} / I _{(100). )} (For example, 49%). Second, in the conventional FAPbI ₃ , the intensity of the third peak is smaller than the intensity of the first peak, whereas in the perovskite type compound in the present embodiment, the intensity of the third peak is larger than the intensity of the first peak. large.

_{When the present inventor theoretically calculated the X-ray diffraction pattern of FAPbI 3} while changing the ratio of elements such as iodine and lead, the above-mentioned characteristics found in the perovskite-type compound in the present embodiment have iodine deficiency. It was found to be a feature of the diffraction peaks that appear in some cases. Therefore, this XRD measurement result indicates that the perovskite-type compound of the present embodiment has more iodine deficiency than _{the conventional FAPBI 3 perovskite-type compound.}

<Fluorescence spectrum>
In the perovskite-type compound of the present embodiment, the peak of the fluorescence spectrum is located on the longer wavelength side than _{the conventional FAPbI 3.} The conventional FAPbI ₃ shows a fluorescence spectrum having a peak top at 830 nm by excitation with visible light (for example, 532 nm), whereas the perovskite-type compound of the present embodiment has a fluorescence spectrum having a peak top at 880 nm or more and 905 nm or less, for example. The spectrum is shown. This is because the long wavelength absorption by the perovskite type compound in this embodiment is not due to the impurity level, but has a high electron density distribution in the conduction band and the valence band like a so-called direct transition type semiconductor. It is shown that.

(Physical characteristics of perovskite-type compounds)
The perovskite-type compound in the present embodiment can exhibit the following physical properties useful as a light absorbing material for a solar cell.

<Band gap>
The perovskite-type compound in the present embodiment may have a bandgap closer to 1.4 eV than _{the conventional FAPBI 3 (bandgap 1.49 eV).} The bandgap of the perovskite-type compound of the present embodiment is preferably about 1.4 eV, for example, 1.35 eV or more and less than 1.45 eV.

The bandgap of the perovskite-type compound is calculated, for example, by measuring the absorbance of the perovskite-type compound.

The reason why the perovskite-type compound in the present embodiment has a narrower bandgap than before is considered as follows.

As described above, in the conventional FAPbI _{3 perovskite type crystal, it is difficult to arrange a plurality of PbI 6} octahedrons in a zigzag pattern and linearly due to the size of each of the constituent ions. On the other hand, in the perovskite-type compound of the present embodiment, a part of the iodine sites constituting the _{PbI 6 octahedron is deleted in the perovskite crystal structure.} There are more such iodine-deficient sites than _{conventional FAPbI 3.} It is considered that the iodine-deficient site relaxes the structural strain due ^{to the large FA + and} _{enhances the symmetry, and the arrangement of the PbI 6} octahedron is more linear than before. As a result, it is considered that the band gap is narrowed and it is possible to realize the best efficiency as a light absorbing material for a solar cell of 1.4 eV.

<Fluorescence life>
The "fluorescence lifetime" refers to the lifetime of fluorescence (decay rate constant) generated when electrons in the conduction band and holes in the valence band are recombined after charge separation. FIG. 1 is a diagram showing the relationship between the fluorescence lifetime and conversion efficiency of a perovskite-type compound in a perovskite solar cell, which was obtained by the study of the present inventor. As can be seen from FIG. 1, in a solar cell, the longer the fluorescence lifetime, the lower the rate of recombination. As a result, the number of electrons and holes that can be taken out increases, so that the conversion efficiency becomes high.

The fluorescence lifetime is measured at a wavelength of 532 nm, which is excited and has the highest fluorescence intensity. The measurement temperature is 25 ° C. Here, a quadratic linear approximation is performed from the time with the highest intensity count, and the decay rate constant of the component having a long lifetime is calculated as the "fluorescence lifetime".

Conventionally _{, the fluorescence lifetime of the FAPbI 3} perovskite type compound has been about 5 ns to 10 ns, for example. On the other hand, the fluorescence lifetime of the perovskite-type compound in the present embodiment is longer than before, for example, more than 10 ns, preferably 15 ns or more. Therefore, it is possible to further improve the conversion efficiency of the solar cell.

(Manufacturing method of light absorbing material)
Next, an example of a method for producing a perovskite-type compound in the present embodiment will be described with reference to the drawings. Here, the crystal growth method in the liquid phase will be described as an example, but the production method of the present embodiment is not limited to this.

First, as shown in FIG. 2A, the γ- butyrolactone (γ-BL), is added and PbI _2, and FAI of PbI ₂ the same molar amount. Then, for example, it is dissolved in an oil bath 41 heated to 40 ° C. or higher and 80 ° C. or lower (here, 80 ° C.) to obtain a yellow solution (first solution) 51.

After cooling the first solution 51 to room temperature once, as shown in FIG. 2B, pure water is mixed with the first solution 51 with good stirring to obtain a second solution 52. The amount of pure water added may be, for example, 0.1 vol% or more and 1.0 vol% or less (0.7 vol% in this case) in terms of the volume ratio with respect to the first solution 51. Subsequently, the obtained second solution 52 is left (preserved) at room temperature.

After that, as shown in FIG. 2C, the second solution 52 is placed in a test tube and allowed to stand in an oil bath 41 heated to 90 ° C. or higher and 130 ° C. or lower (110 ° C. in this case). As a result, black crystals 54 are deposited inside the liquid. The time (precipitation time) Td to be allowed to stand in the oil bath 41 may be set to, for example, 0.5 hours or more and 5 hours or less, preferably 1 hour or more and 3 hours or less. After this, the crystals 54 are thoroughly washed with acetone. In this way, a perovskite-type compound (FAPBI ₃ crystal) can be obtained.

The obtained FAPBI ₃ crystal has an iodine deficiency. Iodine deficiency can be adjusted by process conditions. For example, the amount of iodine deficiency may change depending on the time Ts at which the second solution 52 is stored. The longer the storage time Ts, the longer the time for the second solution 52 to be exposed to air (oxygen). Therefore, the iodine ions (I ⁻ ) in the second solution 52 react with oxygen to produce iodine (I ₂ ). Is easy to release (see the formula below). Therefore, it is possible to increase the amount of iodine deficiency.
2I ^- → I ₂ + 2e ^{-
_{O 2 + 4e - + 4H 2}} O → 4OH -
The storage time Ts cannot be unequivocally determined because it varies depending on other process conditions, but may be, for example, 1 hour or more and 30 days or less.

The iodine deficiency can also be adjusted by the amount of water added to the first solution 51. As the amount of water added increases, the amount of iodine deficiency tends to increase. However, as described above, the amount of water added to the first solution 51 is adjusted within the range of, for example, 0.1 vol% or more and 1.0 vol% or less. If the amount of water added is too large (for example, more than 1.0 wt%), crystal precipitation may not occur. Further, if the amount of water added is too small (for example, less than 0.1 vol%), iodine deficiency may not occur, or the iodine deficiency amount may be less than a predetermined amount.

FIG. 3A is an enlarged photograph of a perovskite-type compound prepared with a precipitation time Td of 1 hour. FIG. 3B is an enlarged photograph of a perovskite-type compound prepared with a precipitation time Td of 3 hours. As the precipitation time Td becomes longer, the crystal size becomes larger, and it can be seen that the crystal size can be adjusted by the precipitation time Td.

Of the three HSPs (Hansen solubility parameters) in the first solution and the solvent used in the second solution, σ _h (energy due to intermolecular hydrogen bonds) and σ _p (energy due to intermolecular dipole interaction) are , May be in the following range.
4 <σ _h <14 (1)
10 <σ _p <22 (2)
Alternatively, σ _h and σ _p may be in the following range.
5 <σ _h <8 (3)
13 <σ _p <18 (4)

In a solvent in which HSP satisfies the above range, the intensity of interaction between lead halide or alkylammonium halide, which is a precursor of a perovskite-type compound, and a solvent molecule is within an appropriate range. Therefore, it is possible to achieve both dissolution of the precursor molecule in a solvent and precipitation of a perovskite-type compound by ITC (reverse temperature-dependent crystallization). ITC refers to a phenomenon in which the solubility of a solute in a solvent decreases as the temperature rises, and crystals precipitate.

Specific examples of such a solvent include lactone-based solvents. Examples of lactone-based solvents include γ-butyl lactone, caprolactone, γ-valerolactone, γ-hexanolactone, γ-nononalactone and derivatives thereof. A plurality of lactone solvents may be mixed and used so that the HSP satisfies the above range.

A lactone-based solvent having an alkyl group in the side chain may be used. Examples of lactone-based solvents having an alkyl group include γ-valerolactone (side chain: -CH ₃ ), γ-hexanolactone (side chain: -CH ₂ CH ₃ ), and γ-nononalactone (side chain:-(side chain:-(). CH ₂ ) ₄ CH ₃ ) can be mentioned. According to the study by the present inventor, it was confirmed that the precipitation temperature of the perovskite-type compound decreases as the alkyl group in the side chain of the lactone-based solvent becomes longer. Specifically, the precipitation temperature of γ-butyl lactone having no side chain was 120 ° C, but that of γ-valerolactone was 80 ° C, that of γ-hexanolactone was 70 ° C, and that of γ-nononalactone was 30 ° C. It was. When the crystal precipitation temperature is low, the energy consumed during production can be reduced, which is industrially useful.

(Examples and Comparative Examples)
Since the perovskite-type compounds of Examples and Comparative Examples (hereinafter, simply abbreviated as "compounds") were prepared and their physical properties were evaluated, the methods and results will be described.

<Preparation of compounds of Examples and Comparative Examples>
[Examples 1 to 10]
The compounds of Examples were prepared by the methods described above with reference to FIGS. 2A to 2C. _{Specifically, an oil bath in which 1 mol / L PbI 2} (manufactured by Tokyo Kasei) and 1 mol / L FAI (manufactured by Tokyo Kasei) are added to γ-butyl lactone (γ-BL) and heated to 80 ° C. It was dissolved in the solution to obtain a yellow solution (first solution). Next, the first solution was once cooled to room temperature, and then 0.7 vol% pure water by volume was mixed with good stirring. The obtained liquid (second solution) was stored at room temperature for a predetermined time (storage time Ts).

After this, the second solution was placed in a test tube and allowed to stand in an oil bath heated to 110 ° C. The standing time (precipitation time Td) was set to 1 hour. As a result, black crystals were precipitated inside the liquid. Then, the crystals were thoroughly washed with acetone _{to obtain the compound of Example (FAPbI 3} crystals). Here, the compounds of Examples 1 to 10 were prepared by different storage times Ts of the second solution. Table 1 shows the storage time Ts of each example.

[Comparative Examples 1 to 3]
First, _{a DMSO (dimethyl sulfoxide) solution containing PbI 2} at a concentration of 1 mol / L and FAI at a concentration of 1 mol / L was prepared. Next, this solution was applied onto the substrate by a spin coating method. As the substrate, a conductive glass substrate (manufactured by Nippon Sheet Glass) having a thickness of 1 mm on which _{two fluorine-doped SnO layers were formed was used.} Then, the substrate was heat-treated on a hot plate at 150 ° C. _{to obtain compounds of Comparative Examples 1 to 3 (FAPbI 3} membrane).

<Composition analysis>
The composition of the compounds of each example and comparative example was analyzed. Here, RBS and NRA measurements were carried out on the compounds of Example 1 and Comparative Example 1, and XPS measurements were carried out on the compounds of Examples 2 to 5 and Comparative Example 2. In addition, EPMA (electron probe microanalyzer) measurement was performed on the compounds of Examples 6 and 7 and Comparative Example 3.

The measurement results are shown in Table 1. Table 1 shows the elemental ratio (atomic%) of the composition of each material obtained by XPS, RBS, NRA measurement or EPMA measurement, and the elemental ratio standardized with the elemental ratio of Pb as 1 (elemental ratio to Pb). Is shown. Further, the iodine deficiency rate x was calculated assuming that the element ratio of I to Pb was 3 × (1-x), which is shown in Table 1.

From the results shown in Table 1, it was confirmed that the compound of the example showed a higher iodine deficiency rate x than the compound of the comparative example, although the measurement result of the element ratio differed depending on the analysis method.

According to XPS measurement, the element ratio of I to Pb of the compound in the example was 1.8 or more and 2.7 or less (iodine deficiency rate x: 0.1 or more and 0.4 or less), and in this example, 2.1 or more and 2. It was 7 or less (iodine deficiency rate x: 0.1 or more and 0.3 or less).

According to the RBS / NRA measurement, for example, the element ratio of I to Pb was 2.9 or less (iodine deficiency rate x: 0.03 or more). According to the RBS measurement, the composition ratio can be calculated with high accuracy. For example, even when other compounds are deposited on the perovskite membrane, the composition of the perovskite membrane can be analyzed with high accuracy.

Next, the measurement result of the XPS spectrum will be described. 4A to 4D are diagrams showing XPS spectra of the compounds of Example 2 and Comparative Example 2, respectively, showing spectra near the binding energy corresponding to the C1s orbit, N1s orbit, Pb4f orbit and I3d5 orbit, respectively.

As can be seen from the results shown in FIGS. 4A to 4D, the spectra corresponding to the N1s orbit, the Pb4f orbit and the I3d5 orbit are substantially the same in Example 2 and Comparative Example 2. On the other hand, the spectra corresponding to the C1s orbitals are different from each other. Specifically, in Example 2, the ratio of the intensity of the peak of C1s located at 285 to 288 eV to the intensity of the peak of C1s located at 288 to 292 eV is 30% or more, which is higher than the above ratio of Comparative Example 2. Is also big. This indicates that the electronic state close to ^{FA +} is changed between the compound of Example 2 and the compound of Comparative Example 2. Although not shown, XPS spectra in other examples show the same tendency as in Example 1.

<Crystal structure analysis>
XRD measurements were performed on the compounds of Examples 1 to 5 and Comparative Example 1.

FIG. 5A is a diagram showing the XRD measurement results of the material of Example 1, in which the horizontal axis represents 2θ and the vertical axis represents the X-ray diffraction intensity. FIG. 5B is a diagram showing an XRD pattern of the compound of Comparative Example 1. Here, CuKα rays are used as X-rays. The X-ray diffraction patterns of the other examples also show the same tendency as that of the first embodiment, and thus the illustration is omitted.

As can be seen from FIGS. 5A and 5B, the X-ray diffraction patterns of the materials of Examples and Comparative Examples belong to the (100) plane, and the first peak located at 13.9 ° ≤ 2θ ≤ 14.1 °. , The second peak attributed to the (111) plane and located at 23.5 ° ≤ 2θ ≤ 24.5 °, and the third peak attributed to the (200) plane and located at 27 ° ≤ 2θ ≤ 29 °. have.

Table 2 shows _{the intensities I (100)} , I ₍₁₁₁₎ , and I ₍₂₀₀₎ of the first peak, the second peak, and the third peak in each Example and Comparative Example. Further, since the intensity ratio I ₍₁₁₁₎ / I ₍₁₀₀₎ of the second peak to the first peak and the intensity ratio I ₍₂₀₀₎ / I ₍₁₀₀₎ of the second peak to the first peak were calculated, Table 2 Shown in.

From the results shown in Table 2, the first peak intensity ratio I to the second peak in the compound of Example 5 from Example _{1 (111) / I (100} ) , the intensity ratio of the Comparative Example I ₍₁₁₁₎ / I _{( 100)} Found to be smaller than (49%). The intensity ratio I ₍₁₁₁₎ / I ₍₁₀₀₎ in the examples was, for example, more than 0% and 40% or less. Further, in Comparative Example 1, the intensity of the third peak is smaller than the intensity of the first peak, whereas in Examples 1 to 5, the intensity of the third peak is larger than the intensity of the first peak. _{That is, the intensity ratio I (200)} / I ₍₁₀₀₎ of the third peak to the first peak in Examples 1 to 5 was more than 100%. From such a characteristic of the intensity ratio, it was confirmed that the compounds of Examples 1 to 5 had more iodine deficiency than the compounds of Comparative Example 1.

Further, the compounds of Example 1 and Comparative Example 1 were subjected to XRD measurement using a more accurate XRD apparatus, and the fourth peak attributed to the (110) plane and the fifth peak attributed to the (220) plane. The position of was investigated in detail.

13A and 13B are diagrams showing XRD patterns of the compounds of Example 1 and Comparative Example 1. The solid line is the XRD pattern of the compound of Example 1, and the broken line is the XRD pattern of the compound of Comparative Example 1. Further, FIG. 13A shows the diffraction intensity at the diffraction angle 2θ: 19.2 ° to 20.2 °, and FIG. 13B shows the diffraction intensity at the diffraction angle 2θ: 39.4 ° to 40.8.

As can be seen from FIGS. 13A and 13B, the XRD pattern of Example 1 is located at the fourth peak located at 19.65 ° ≤ 2θ ≤ 19.71 ° and at 39.98 ° ≤ 2θ ≤ 40.10 °. It has a fifth peak.

The fourth peak in Example 1 is located at 2θ = 19.68 °, which is about 0.1 ° lower than the peak (2θ = 19.72 °) attributed to the (110) plane in Comparative Example 1. It's shifting. Similarly, the fifth peak of Example 1 is located at 2θ = 40.04 °, which is about 0.1 ° lower than the peak (2θ = 40.11 °) attributed to the (220) plane in Comparative Example 1. It is shifting to the angle side. This indicates that _{the unit cell of the FAPbI 3} crystal in the compound of Example 1 is larger than that of the compound of Comparative Example 1. Generally, in the FAPbI ₃ crystal, the larger the unit cell, the smaller the bandgap. Therefore, it is confirmed that the compound of Example 1 has a smaller bandgap than the compound of Comparative Example 1.

<Fluorescence measurement / fluorescence life>
Fluorescence measurement and fluorescence lifetime measurement were performed on the compounds of Examples 1 to 5 and Comparative Example 1 using a laser of 532 nm as a light source.

FIG. 6 is a diagram showing measurement results of fluorescence spectra obtained by fluorescence measurement using a laser at 532 nm as a light source in the compounds of Example 1 and Comparative Example 1. The horizontal axis is the wavelength and the vertical axis is the fluorescence intensity. Since the measurement results of the other examples show the same tendency as that of the first embodiment, the illustration is omitted.

As shown in FIG. 6, the fluorescence spectrum of the compound of Comparative Example 1 has a peak at 830 nm, whereas the fluorescence spectrum of the compound of Example 1 has a peak at 890 nm. That is, it can be seen that the peak of the fluorescence spectrum of the compound of Example 1 is located on the longer wavelength side than that of Comparative Example 1.

Table 3 shows the wavelength at which the fluorescence intensity is highest in each Example and Comparative Example (hereinafter referred to as peak wavelength). From the results shown in Table 3, it was found that the peak wavelengths in Examples 1 to 5 were 880 nm or more and 905 nm or less.

Next, the fluorescence lifetime was measured at the wavelength at which the fluorescence intensity was highest (peak wavelength). The measurement temperature was 25 ° C.

FIG. 7 shows the fluorescence attenuation curves of the compounds of Example 1 and Comparative Example 1. The horizontal axis of FIG. 7 represents time, and the vertical axis represents the number of counts. For each curve, a quadratic linear approximation was performed from the time with the highest intensity count, and the decay rate constant of the long-lived component was calculated as the fluorescence lifetime. The fluorescence lifetime was calculated in the same manner for Examples 2 to 5. The results are shown in Table 3.

From the results shown in Table 3, it was confirmed that the compounds of Examples 1 to 5 had a longer fluorescence lifetime than the compounds of Comparative Example 1.

<Absorbance measurement>
The absorbance of the compounds of Examples 1 to 5 and Comparative Example 1 was measured, and the wavelengths of the band gap and the absorption edge were calculated.

FIG. 8 is a diagram showing absorption spectra of the compounds of Example 1 and Comparative Example 1, in which the horizontal axis represents wavelength and the vertical axis represents absorbance. In the compound of Comparative Example 1, the wavelength of the absorption edge corresponding to the band gap was around 830 nm, and the band gap was 1.49 eV. On the other hand, in the compound of Example 1, the wavelength of the absorption edge was around 885 nm, and the band gap was about 1.4 eV. Similarly, the wavelengths and band gaps of the absorption edges of Examples 2 to 5 were determined, and the results are shown in Table 4.

The band gap was calculated as follows. Assuming that the absorbance is α and the bandgap is Eg, α ² is proportional to (hν-Eg). Here, h is Planck's constant, ν is frequency, and hν is about 1240 / λ. Here, λ is the absorption wavelength. ^{Based on this relationship, α 2} was set on the vertical axis (y-axis) and 1240 / λ was set on the horizontal axis (x-axis), a linear approximation was performed near the absorption edge, and the x-axis intercept was defined as the bandgap Eg.

From this result, it was found that the wavelength of the absorption edge in the compounds of Examples 1 to 5 was located on the longer wavelength side than that of the compound of Comparative Example 1. Further, it was confirmed that the compounds of Examples 1 to 5 have a band gap of 1.4 eV or a vicinity of 1.4 eV and can contribute to high conversion efficiency.

It should be noted that the results of the plurality of types of analysis performed on each of the compounds of Examples and Comparative Examples do not necessarily target the same position and the same depth of the compound. For example, in the RBS measurement, a region having a width of 1 mm and a depth of 1 μm was analyzed, and in the XPS measurement, a region having a width of 100 μm and a depth of several nm was analyzed. Further, the fluorescence wavelength and the fluorescence lifetime were measured in the region of the compound having a width of 100 μm and a depth of 0.5 μm.

(Structure and manufacturing method of solar cells)
Hereinafter, the structure and manufacturing method of the solar cell using the light absorbing material of the present embodiment will be described with reference to the drawings.

FIG. 9 is a schematic cross-sectional view showing an example of the solar cell of the present embodiment.

In the solar cell 100, the first electrode 22, the light absorption layer 5, and the second electrode 6 are laminated in this order on the substrate 1. The light absorbing material of the light absorbing layer 5 contains the _{FAPbI type 3 compound in the present embodiment.} The solar cell 100 does not have to have the substrate 1.

Next, the basic effects of the solar cell 100 will be described. When the solar cell 100 is irradiated with light, the light absorption layer 5 absorbs the light and generates excited electrons and holes. The excited electrons move to the first electrode 2. On the other hand, the holes generated in the light absorption layer 5 move to the second electrode 6. As a result, the solar cell 100 can draw current from the first electrode 2 as the negative electrode and the second electrode 6 as the positive electrode.

The solar cell 100 can be manufactured, for example, by the following method. First, the first electrode 2 is formed on the surface of the substrate 1 by a chemical vapor deposition method, a sputtering method, or the like. Next, the light absorption layer 5 is formed on the first electrode 2. _{For example, a perovskite-type compound (FAPbI 3} crystal) produced by the above-mentioned method with reference to FIGS. 2A to 2C may be cut out to a predetermined thickness to form a light absorption layer 5 and installed on the first electrode. .. Subsequently, the solar cell 100 can be obtained by forming the second electrode 6 on the light absorption layer 5.

Hereinafter, each component of the solar cell 100 will be specifically described.

<Board 1>
The substrate 1 is an ancillary component. The substrate 1 serves to hold each layer of the solar cell 100. The substrate 1 can be formed from a transparent material. For example, a glass substrate or a plastic substrate (including a plastic film) can be used. Further, when the first electrode 2 has sufficient strength, each layer can be held by the first electrode 2, so that the substrate 1 does not necessarily have to be provided.

<First electrode 2>
The first electrode 2 has conductivity. Further, the first electrode 2 does not form ohmic contact with the light absorption layer 5. Further, the first electrode 2 has a blocking property for holes from the light absorption layer 5. The blocking property for holes from the light absorption layer 5 is a property that allows only electrons generated in the light absorption layer 5 to pass through and does not allow holes to pass through. The material having such a property is a material having a Fermi level lower than the energy level at the lower end of the valence band of the light absorption layer 5. Specific examples include aluminum.

Further, the first electrode 2 has translucency. For example, it transmits light from the visible region to the near infrared region. The first electrode 2 can be formed, for example, by using a transparent and conductive metal oxide. Examples of such metal oxides include indium-tin composite oxides, antimony-doped tin oxide, fluorine-doped tin oxide, boron, aluminum, gallium, zinc oxide doped with at least one of indium, or these. Complex of.

Further, the first electrode 2 can be formed by using a non-transparent material and providing a pattern through which light is transmitted. The pattern through which light is transmitted includes, for example, a linear, wavy, lattice pattern, a punching metal pattern in which a large number of fine through holes are regularly or irregularly arranged, or a negative / positive pattern. An inverted pattern can be mentioned. When the first electrode 2 has these patterns, light can be transmitted through a portion where the electrode material does not exist. Non-transparent electrode materials include, for example, platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or alloys containing any of these. Moreover, a carbon material having conductivity can also be used.

The light transmittance of the first electrode 2 may be, for example, 50% or more, or 80% or more. The wavelength of light to be transmitted depends on the absorption wavelength of the light absorption layer 5. The thickness of the first electrode 2 is, for example, in the range of 1 nm or more and 1000 nm or less.

<Light absorption layer 5>
The light absorbing material of the light absorbing layer 5 contains the perovskite-type compound of the present embodiment. The thickness of the light absorption layer 5 depends on the magnitude of the light absorption, but is, for example, 100 nm or more and 1000 nm or less. The light absorption layer 5 may be formed by cutting out _{a FAPbI 3 crystal as described above.} The method of forming the light absorption layer 5 is not particularly limited. For example, it can also be formed by a coating method using a solution containing a perovskite-type compound.

<Second electrode 6>
The second electrode 6 has conductivity. Further, the second electrode 6 does not make ohmic contact with the light absorption layer 5. Further, it has a blocking property for electrons from the light absorption layer 5. The blocking property for electrons from the light absorption layer 5 is a property that allows only holes generated in the light absorption layer 5 to pass through and does not allow electrons to pass through. The material having such properties is a material having a Fermi level higher than the energy level at the upper end of the conduction band of the light absorption layer 5. Specific examples include carbon materials such as gold and graphene.

FIG. 10 is a schematic cross-sectional view showing another example of the solar cell of the present embodiment. The solar cell 200 is different from the solar cell 100 shown in FIG. 9 in that it includes an electron transport layer. Components having the same functions and configurations as the solar cell 100 are designated by the same reference numerals as those of the solar cell 100, and the description thereof will be omitted as appropriate.

In the solar cell 200, the first electrode 22, the electron transport layer 3, the light absorption layer 5, and the second electrode 6 are laminated in this order on the substrate 1. The solar cell 200 does not have to have the substrate 1.

Next, the basic effects of the solar cell 200 will be described. When the solar cell 100 is irradiated with light, the light absorption layer 5 absorbs the light and generates excited electrons and holes. The excited electrons move to the first electrode 22 via the electron transport layer 3. On the other hand, the holes generated in the light absorption layer 5 move to the second electrode 6. As a result, the solar cell 200 can draw current from the first electrode 22 as the negative electrode and the second electrode 6 as the positive electrode.

Further, in the present embodiment, the electron transport layer 3 is provided. Therefore, the first electrode 22 does not have to have a blocking property for holes from the light absorption layer 5. Therefore, the range of material selection for the first electrode 22 is widened.

The solar cell 200 of the present embodiment can be manufactured by the same method as the solar cell 100 shown in FIG. The electron transport layer 3 is formed on the first electrode 22 by a sputtering method or the like.

Hereinafter, each component of the solar cell 200 will be specifically described.

<First electrode 22>
The first electrode 22 has conductivity. The first electrode 22 may have the same configuration as the first electrode 2. In this embodiment, since the electron transport layer 3 is used, the first electrode 22 does not have to have a blocking property for holes from the light absorption layer. That is, the material of the first electrode 22 may be a material that makes ohmic contact with the light absorption layer.

The first electrode 22 has translucency. For example, it transmits light from the visible region to the near infrared region. The first electrode 22 can be formed by using a transparent and conductive metal oxide. Examples of such metal oxides include indium-tin composite oxides, antimony-doped tin oxide, fluorine-doped tin oxide, boron, aluminum, gallium, zinc oxide doped with at least one of indium, or zinc oxide. These composites can be mentioned.

Further, as the material of the first electrode 22, a non-transparent material can also be used. In that case, similarly to the first electrode 2, the first electrode 22 is formed in a pattern through which light is transmitted. Non-transparent electrode materials include, for example, platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or alloys containing any of these. Moreover, a carbon material having conductivity can also be used.

The light transmittance of the first electrode 22 may be, for example, 50% or more, or 80% or more. The wavelength of light to be transmitted depends on the absorption wavelength of the light absorption layer 5. The thickness of the first electrode 22 is, for example, 1 nm or more and 1000 nm or less.

<Electron transport layer 3>
The electron transport layer 3 includes a semiconductor. The electron transport layer 3 may be a semiconductor having a band gap of 3.0 eV or more. By forming the electron transport layer 3 with a semiconductor having a band gap of 3.0 eV or more, visible light and infrared light can be transmitted to the light absorption layer 5. Examples of semiconductors include organic or inorganic n-type semiconductors.

Examples of the organic n-type semiconductor include imide compounds, quinone compounds, and fullerenes and derivatives thereof. Further, as the inorganic n-type semiconductor, for example, an oxide of a metal element or a perovskite-type oxide can be used. Examples of metal element oxides include Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, and Cr. Oxides can be used. A more specific example is TiO ₂ . Examples of perovskite-type oxides include SrTiO ₃ and CaTIO ₃ .

Further, the electron transport layer 3 may be formed of a substance having a band gap larger than 6 eV. Examples of the substance having a band gap larger than 6 eV include halides of alkali metals or alkaline earth metals such as lithium fluoride or calcium fluoride, alkali metal oxides such as magnesium oxide, and silicon dioxide. In this case, in order to ensure the electron transportability of the electron transport layer 3, the electron transport layer 3 is configured to have, for example, 10 nm or less.

The electron transport layer 3 may include a plurality of layers made of different materials.

FIG. 11 is a schematic cross-sectional view showing an example of the solar cell of the present embodiment. The solar cell 300 differs from the solar cell 200 shown in FIG. 10 in that it includes a porous layer. Components having the same functions and configurations as the solar cell 200 are designated by the same reference numerals as those of the solar cell 200, and the description thereof will be omitted as appropriate.

In the solar cell 300, the first electrode 22, the electron transport layer 3, the porous layer 4, the light absorption layer 5, and the second electrode 6 are laminated in this order on the substrate 1. The porous layer 4 contains a porous body. The porous body contains pores. The solar cell 300 does not have to have the substrate 1.

The pores in the porous layer 4 are connected from a portion in contact with the light absorption layer 5 to a portion in contact with the electron transport layer 3. As a result, the material of the light absorption layer 5 can fill the pores of the porous layer 4 and reach the surface of the electron transport layer 3. Therefore, since the light absorption layer 5 and the electron transport layer 3 are in contact with each other, electrons can be directly transferred.

Next, the basic effects of the solar cell 100 will be described. When the solar cell 100 is irradiated with light, the light absorption layer 5 absorbs the light and generates excited electrons and holes. The excited electrons move to the first electrode 22 via the electron transport layer 3. On the other hand, the holes generated in the light absorption layer 5 move to the second electrode 6. As a result, the solar cell 100 can draw current from the first electrode 22 as the negative electrode and the second electrode 6 as the positive electrode.

Further, by providing the porous layer 4 on the electron transport layer 3, the effect that the light absorption layer 5 can be easily formed can be obtained. That is, by providing the porous layer 4, the material of the light absorption layer 5 penetrates into the pores of the porous layer 4, and the porous layer 4 becomes a scaffold for the light absorption layer 5. Therefore, the material of the light absorption layer 5 is unlikely to be repelled or aggregated on the surface of the porous layer 4. Therefore, the light absorption layer 5 can be formed as a uniform film.

Further, it is expected that the light scattering caused by the porous layer 4 has the effect of increasing the optical path length of the light passing through the light absorption layer 5. As the optical path length increases, it is predicted that the amount of electrons and holes generated in the light absorption layer 5 will increase.

The solar cell 300 can be manufactured by the same method as the solar cell 200. The porous layer 4 is formed on the electron transport layer 3 by, for example, a coating method.

<Porous layer 4>
The porous layer 4 serves as a base for forming the light absorption layer 5. The porous layer 4 does not inhibit the light absorption of the light absorption layer 5 and the electron transfer from the light absorption layer 5 to the electron transport layer 3.

The porous layer 4 contains a porous body. Examples of the porous body include an insulating or porous body in which semiconductor particles are connected. As the insulating particles, for example, particles of aluminum oxide and silicon oxide can be used. Inorganic semiconductor particles can be used as the semiconductor particles. As the inorganic semiconductor, an oxide of a metal element, a perovskite oxide of a metal element, a sulfide of a metal element, and a metal chalcogenide can be used. Examples of metal element oxides include Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, Examples include Cr oxide. A more specific example is TiO ₂ . Examples of perovskite oxides, which are metal elements, include SrTIO ₃ and CaTIO ₃ . Examples of metal element sulfides include CdS, ZnS, In ₂ S ₃ , PbS, Mo ₂ S, WS ₂ , Sb ₂ S ₃ , Bi ₂ S ₃ , ZnCdS ₂ , and Cu ₂ S. Examples of metallic chalcogenides include CdSe, In ₂ Se ₃ , WSe ₂ , HgS, PbSe, and CdTe.

The layer of the porous layer 4 is preferably 0.01 μm or more and 10 μm or less, and more preferably 0.1 μm or more and 1 μm or less. Further, it is desirable that the surface roughness of the porous layer 4 is large. Specifically, the surface roughness coefficient given by the effective area / projected area is preferably 10 or more, and more preferably 100 or more. The projected area is the area of the shadow formed behind the object when it is illuminated with light from the front. The effective area is the actual surface area of an object. The effective area can be calculated from the volume obtained from the projected area and thickness of the object and the specific surface area and bulk density of the materials constituting the object.

FIG. 12 is a schematic cross-sectional view showing another example of the solar cell of the present embodiment.

The solar cell 400 differs from the solar cell 300 shown in FIG. 11 in that it includes a hole transport layer. Components having the same functions and configurations as the solar cell 100 are designated by the same reference numerals as those of the solar cell 100, and the description thereof will be omitted as appropriate.

In the solar cell 400, the first electrode 32, the electron transport layer 3, the porous layer 4, the light absorption layer 5, the hole transport layer 7, and the second electrode 36 are laminated in this order on the substrate 31. Has been done. The solar cell 200 does not have to have the substrate 31.

Next, the basic operation and effect of the solar cell 400 of the present embodiment will be described.

When the solar cell 400 is irradiated with light, the light absorption layer 5 absorbs the light and generates excited electrons and holes. The excited electrons move to the electron transport layer 3. On the other hand, the holes generated in the light absorption layer 5 move to the hole transport layer 7. The electron transport layer 3 is connected to the first electrode 32, and the hole transport layer 7 is connected to the second electrode 36. As a result, the solar cell 400 can draw current from the first electrode 32 as the negative electrode and the second electrode 36 as the positive electrode.

The solar cell 400 has a hole transport layer 7 between the light absorption layer 5 and the second electrode 36. Therefore, the second electrode 36 does not have to have a blocking property for electrons from the light absorption layer 5. Therefore, the range of material selection for the second electrode 36 is widened.

Hereinafter, each component of the solar cell 400 will be specifically described. The description of the elements common to the solar cell 300 will be omitted.

<First electrode 32 and second electrode 36>
As described above, the second electrode 36 does not have to have a blocking property for electrons from the light absorption layer 5. That is, the material of the second electrode 36 may be a material that makes ohmic contact with the light absorption layer 5. Therefore, the second electrode 36 can be formed so as to have translucency.

At least one of the first electrode 32 and the second electrode 36 has translucency and is configured in the same manner as the first electrode 2 of the solar cell 100.

One of the first electrode 32 and the second electrode 36 does not have to have translucency. That is, it is not always necessary to use a material having translucency, and it is not necessary to have a pattern including an opening portion for transmitting light.

<Board 31>
The configuration can be the same as that of the substrate 1 shown in FIG. Further, when the second electrode 36 has a translucent property, the material of the substrate 31 may be a material having no translucent property. For example, as the material of the substrate 31, a metal, ceramics, or a resin material having low permeability can be used.

<Hole transport layer 7>
The hole transport layer 7 is composed of an organic substance, an inorganic semiconductor, or the like. The hole transport layer 7 may include a plurality of layers made of different materials.

The thickness of the hole transport layer 7 is preferably 1 nm or more and 1000 nm or less, and more preferably 10 nm or more and 50 nm or less. Within this range, sufficient hole transportability can be exhibited. Moreover, since low resistance can be maintained, photovoltaic power generation can be performed with high efficiency.

As a method for forming the hole transport layer 7, a coating method or a printing method can be adopted. Examples of the coating method include a doctor blade method, a bar coating method, a spray method, a dip coating method, and a spin coating method. Examples of the printing method include a screen printing method. Further, if necessary, a plurality of materials may be mixed to prepare a hole transport layer 7, and the hole transport layer 7 may be pressurized or fired. When the material of the hole transport layer 7 is an organic low molecular weight substance or an inorganic semiconductor, it can be produced by a vacuum vapor deposition method or the like.

The hole transport layer 7 may contain a supporting electrolyte and a solvent. The supporting electrolyte and the solvent have the effect of stabilizing the holes in the hole transport layer 7.

Examples of the supporting electrolyte include ammonium salts and alkali metal salts. Examples of the ammonium salt include tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, imidazolium salt and pyridinium salt. Examples of the alkali metal salt include lithium perchlorate and potassium tetrafluoride.

The solvent contained in the hole transport layer 7 is preferably one having excellent ionic conductivity. Both an aqueous solvent and an organic solvent can be used, but an organic solvent is preferable because it stabilizes the solute more. Specific examples include heterocyclic compound solvents such as tert-butylpyridine, pyridine, and n-methylpyrrolidone.

Moreover, you may use an ionic liquid as a solvent alone or mixed with other kinds of solvents. Ionic liquids are desirable because they have low volatility and high flame retardancy.

Examples of the ionic liquid include imidazolium-based, pyridine-based, alicyclic amine-based, aliphatic amine-based, and azonium amine-based ionic liquids such as 1-ethyl-3-methylimidazolium tetracyanoborate. ..

(Examples and Comparative Examples)
Since the solar cells of Examples and Comparative Examples were produced and the element characteristics were evaluated, the method and results will be described.

<Preparation of solar cells of Examples and Comparative Examples>
[Example 11]
As Example 11, a solar cell having the configuration shown in FIG. 10 was produced. As the light absorption layer 5, the compound of Example 1 (FAPbI ₃ crystal) described above was used.

First, the compound of Example 1 was cut into a flat plate shape with a diamond cutter, and the surface was smoothed with sandpaper to obtain a flat plate shape (7 mm × 7 mm) sample having a thickness of 200 μm.

Next, a substrate 1 having an ITO film on its surface was prepared as the first electrode 22, and a SnO ₂ layer as an electron transport layer 3 was formed on the ITO film by a sputtering method. Subsequently, the above-mentioned flat sample was arranged as the light absorption layer 5 on _{the SnO 2 layer.} After that, the second electrode 6 was formed by depositing gold on the surface of the sample. In this way, the solar cell of Example 11 was obtained. The size (area) of the solar cell is 7 mm × 7 mm. Each component is as follows.
Substrate 1: Glass substrate 7 mm x 7 mm, thickness 0.7 mm
First electrode 22: ITO (surface resistance 10 Ω / □)
Electron transport layer 3: SnO ₂ thickness 20 nm
Light absorption layer 5: Compound of Example 1 Thickness 200 μm
Second electrode 6: Au thickness 80 nm

[Comparative Example 4]
A solar cell having the same configuration as that of Example 11 was prepared except that a _{FAPbI 3} film was formed as the light absorption layer 5 on the _{SnO 2} layer, which is the electron transport layer 3, by the same method as in Comparative Example 1. ..

<IPCE efficiency measurement>
In order to evaluate the characteristics of the solar cells of Example 11 and Comparative Example 4, IPCE efficiency measurement (incident photon to currant evaluation efficiency: quantum efficiency measurement for each wavelength) was performed. A solar simulator (OTENTO-SUNV manufactured by Spectrometer Co., Ltd.) was used for the measurement. The energy of the light source was set to 5 mW / cm ² for each wavelength.

The measurement result is shown in FIG. From the results shown in FIG. 14, in Example 11 in which a material having a high iodine deficiency rate was used for the light absorption layer 5, the absorption wavelength range of the solar cell was extended to the longer wavelength side as compared with Comparative Example 4. Do you get it. In the solar cell of Example 11 and Comparative Example 4, when calculating the current value of the reference sunlight (AM1.5G) from the data of the quantum efficiency, respectively, was ^{30mA / cm 2, 24mA / cm} 2. Therefore, it was found that the solar cell of Example 11 has a larger current value under sunlight than the solar cell of Comparative Example 4, and can realize high conversion efficiency.

The light absorbing material according to one embodiment of the present disclosure can be suitably used as a material for a light absorbing layer such as a solar cell. Further, the solar cell according to the embodiment of the present disclosure is useful as a photovoltaic element or an optical sensor.

1, 31 Substrate 2, 22, 32 First electrode 3 Electron transport layer 4 Porous layer 5 Light absorption layer 6, 36 Second electrode 7 Hole transport layer 41 Oil bath 51 First solution 52 Second solution 54 Crystal 100, 200, 300, 400 solar cells

Claims (6)

It has a perovskite type crystal structure, and _comprises mainly a compound represented by _{((NH 2) 2 CH)} PbI 3 (1-x),
I element ratio 3 for Pb in the composition analysis by X-ray photoelectron spectroscopy (1-x) is Ru der 2.37 or 2.63 or less, the light-absorbing material. Before the title compound, having a peak of the fluorescence spectrum inclusive 880 nm 905 nm, the light-absorbing material according to claim 1. X-ray diffraction pattern before the title compound has a first peak located at 13.9 ° ≦ 2θ ≦ 14.1 °, and a second peak located at 23.5 ° ≦ 2θ ≦ 24.5 °, 27 ° It has a third peak located at ≤2θ≤29 ° and has a third peak.
The intensity of the second peak is 40% or less of the intensity of the first peak.
The light absorbing material according to claim 1, wherein the intensity of the third peak is larger than the intensity of the first peak. The light absorbing material according to claim 3 , wherein the X-ray diffraction pattern of the compound further has a fourth peak located at 19.65 ° ≤ 2θ ≤ 19.71 °. The light absorbing material according to claim 3 or 4 , wherein the X-ray diffraction pattern of the compound further has a fifth peak located at 39.98 ° ≤ 2θ ≤ 40.10 °. The first electrode with conductivity and
A light absorption layer located on the first electrode and converting incident light into electric charges,
It is located on the light absorption layer and has a second electrode having conductivity.
The solar cell comprising the light absorbing material according to any one of claims 1 to 5.

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