JP6709443B2 - Compound having a layered perovskite structure - Google Patents

Description

The present invention relates to a compound having a layered perovskite structure, a method for producing the same, and its use.

In recent years, metal halides having a perovskite structure have attracted attention for various applications. The compound having a perovskite structure is composed of cations of A site and B site and anion of X site. An example of such a compound is CH ₃ NH ₃ PbI _{3, in} which the cation at the A site is CH ₃ NH ₃ ⁺ , the cation at the B site is Pb ²⁺ and the anion at the X site. is I ^-, the corresponding. The cation at the B site is bound to the anion at the X site in hexacoordinate, forming a symmetric or asymmetric octahedron. The perovskite structure consisting of only a three-dimensional structure is represented by ABX ₃ or the like as a general formula. It is known that having a perovskite structure is advantageous in moving charges in a material and extending the life of excited carriers (such as electrons and holes) due to light.

Non-Patent Document 1 describes that CH ₃ NH ₃ PbI ₃ can be produced at a low temperature of about 100° C. and is a useful material for applications such as solar cells. A compound having a perovskite structure at a low temperature is selected from the viewpoint that production can be performed with low energy, the device can be simplified, and the heat resistance of the substrate on which the thin film is deposited can be relaxed when the film is formed into a thin film. Being able to manufacture is important.

In Non-Patent Document 2, a compound composed of a formamidinium cation (CHNHNH ₃ ⁺ ), a lead cation (Pb ²⁺ ), and an iodine anion produced at a heating temperature of about 100° C. has a hexagonal crystal structure. Is described.

In Non-Patent Document 3, a compound CsPbI ₃ composed of a cesium cation (Cs ⁺ ), a lead cation (Pb ²⁺ ) and an iodine anion produced at a heating temperature of about 100° C. has an orthorhombic crystal structure. Is described.

In Non-Patent Document 4, a layer structure (two-dimensional structure) can be introduced into a perovskite structure by including an organic molecular cation having a long carbon chain (for example, having 4 carbon atoms) at the A site, and a three-dimensional structure can be introduced. It is described that a 2D-3D structure can also be formed, which periodically includes a 2D structure and a 2D structure. For example, (C ₄ H ₉ NH ₃ ) ₂ (where the A site cation is C ₄ H ₉ NH ₃ ⁺ and CH ₃ NH ₃ ⁺ , the B site cation is Pb ²⁺ , and the X site anion is I ^−. _{CH 3 NH 3) Pb 2 I} 7 is disclosed. Further, it is described that the inclusion of the layered structure increases the binding energy of excitons and the band gap. In particular, it is described that the band gap increases as the interlayer distance increases.

Science 2012, 338, 644. J. Phys. Chem. Lett. 2015, 6, 1249. Nat. Chem. 2014, 5, 5757. J. Am. Soc. 2015, 137, 7843.

However, the heat resistance of CH ₃ NH ₃ PbI ₃ described in Non-Patent Document 1 is not sufficient. Therefore, development of a compound having more excellent heat resistance is required. Further, CH ₃ NH ₃ PbI ₃ described in Non-Patent Document 1 has a small exciton binding energy. Therefore, development of a compound having a large binding energy is desired from the viewpoint of being advantageous for highly efficient light emission.

The compounds described in Non-Patent Documents 3 and 4 cannot form a perovskite structure at low temperatures. Therefore, materials that can form a perovskite structure at a lower temperature have been demanded from the viewpoint that manufacturing can be performed with low energy, the device can be simplified, and the heat resistance of the substrate can be relaxed when forming a thin film.

The (C ₄ H ₉ NH ₃ ) ₂ (CH ₃ NH ₃ )Pb ₂ I ₇ described in Non-Patent Document 2 has insufficient thermal stability and operational stability. Therefore, the development of more stable materials is needed.

The present invention has been made in view of at least some of the problems that the above-mentioned conventional techniques have, a compound that can be manufactured at low temperature, has a large binding energy of excitons, and is excellent in thermal stability, a manufacturing method thereof, and the same. Intended to provide use.

The present inventors have conducted extensive studies and experiments in order to solve the above-mentioned problems of the prior art, as a result, produced by a predetermined method, containing a predetermined cation and a predetermined anion, a compound having a predetermined crystal structure The inventors have found that the above problems can be solved and completed the present invention.

That is, the present invention is as follows.
[1] A compound containing a cation and an anion, wherein the cation contains three or more kinds of cations, and 5 mol% to 90 mol% of the cation is a Group 14 element cation, and 5 the mole% to 90 mole% or less 3 or more carbon atoms and 20 or less of the organic molecules cation a, 90 mole% 5 mole% or more of the cationic following is a alkali metal Kachio emissions, or 30 mole% of the anions 100 mol% or less is a Group 17 element anion, the compound is a crystal, the crystal has a layered perovskite structure, the number of layers of an octahedral network of the Group 14 element cation and anion in the layered perovskite structure A compound having a structure in which is 2 to 8 layers.
[2] The compound according to any one of [1], wherein the organic molecule cation A contains an ammonium cation.
[3] The compound according to [1] or [2], wherein 10 mol% or more and 70 mol% or less of the cation is the Group 1 element cation.
[4] The compound according to any one of [1] to [3], wherein the Group 1 element cation is a cesium cation.
[5] A compound containing a cation and an anion, wherein the cation contains three or more kinds of cations, and 5 mol% or more and 90 mol% or less of the cation is a Group 14 element cation, and 5 Mol% to 90 mol% is an organic molecule cation A, 5 mol% to 90 mol% of the cation is an organic molecule cation B, and 30 mol% to 100 mol% of the anion is a Group 17 element. An anion, the compound is a crystal, the crystal has a layered perovskite structure, and the number of layers of an octahedral network of the group 14 element cation and anion in the layered perovskite structure is 2 or more and 8 or less. The organic molecule cation A has a structure, the organic molecule cation A is an organic molecule ammonium cation having 3 or more and 20 or less carbon atoms, and has one ammonium cation, and the organic molecule cation B is a formamidinium cation or acetamimine. A compound which is at least one cation selected from the group consisting of dinium cations.
[ 6 ] The compound according to [ 5] , wherein 10 mol% or more and 70 mol% or less of the cation is the organic molecule cation B.
[ 7 ] The compound according to any one of [ 1] to [6] , wherein 10 mol% or more and 70 mol% or less of the cation is the organic molecule cation A.
[ 8 ] The compound according to any one of [1] to [7], wherein the organic molecule cation A has 4 or more and 10 or less carbon atoms.
[ 9 ] The compound according to any one of [1] to [ 8 ], wherein the organic molecule cation A has only a straight carbon chain.
[ 10 ] The compound according to any one of [1] to [ 8 ], wherein the carbon chain of the organic molecule cation A contains an aromatic ring.
[ 11 ] The compound according to any one of [1] to [ 10 ], wherein 10 mol% or more and 70 mol% or less of the cation is the Group 14 element cation.
[ 12 ] The compound according to any one of [1] to [ 11 ], wherein the Group 14 element cation is a tin cation or a lead cation.
[ 13 ] The compound according to any one of [1] to [ 12 ], wherein 55 mol% or more and 100 mol% or less of the anion is the Group 17 element anion.
[ 14 ] The compound according to any one of [1] to [ 13 ], including a structure in which the number of layers of the octahedral network of the layered perovskite structure is 2 or more and 3 or less.
[ 15 ] The method for producing the compound according to any one of [1] to [ 14 ], wherein the step of preparing a compound precursor containing the cation and the anion, and the compound precursor at 0° C. And a step of heating at a temperature of 150° C. or lower. In the compound precursor, the cation includes three or more kinds of cations, and 5 mol% to 90 mol% of the cation is a Group 14 element. 5 mol% to 90 mol% of the cation is an organic molecular cation A having 3 to 20 carbon atoms, and 5 mol% to 90 mol% of the cation is a Group 1 element cation, and/ Alternatively, the organic molecular cation B is at least one kind of cation selected from the group consisting of formamidinium cations and acetamidinium cations, and 30 mol% or more and 100 mol% or less of the anions are Group 17 element anions. In the heating step, the compound precursor is a crystal having a layered perovskite structure, and the number of layers of the octahedral network of the group 14 element cations and anions in the layered perovskite structure is 2 or more and 8 layers. A method of manufacturing, wherein the following structure is formed.
[ 16 ] Use of the compound according to any one of [1] to [ 14 ] as a semiconductor material.
[ 17 ] Use of the compound according to any one of [1] to [ 14 ] as a light emitting material.
[ 18 ] Use of the compound according to any one of [1] to [ 14 ] as a solar cell material.
[ 19 ] Use of the compound according to any one of [1] to [ 14 ] as a light absorbing layer of a solar cell.

ADVANTAGE OF THE INVENTION According to this invention, the compound which can be manufactured at low temperature, the binding energy of an exciton is large, and it is excellent in thermal stability, its manufacturing method, and its use can be provided.

Hereinafter, modes for carrying out the present invention (hereinafter, simply referred to as “this embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be variously modified and implemented within the scope of the gist.

The compound of the present embodiment is a compound containing a cation and an anion, wherein the cation contains three or more kinds of cations, and 5 mol% or more and 90 mol% or less of the cation is a Group 14 element cation, 5 mol% to 90 mol% of the cation is an organic molecular cation A having 3 to 20 carbon atoms, and 5 mol% to 90 mol% of the cation is a Group 1 element cation and/or carbon An organic molecular cation B having a number of 2 or less and a sum of carbon number and nitrogen number of 3 or more and 5 or less, 30 mol% or more and 100 mol% or less of the anion is a Group 17 element anion, and the compound is a crystal. The crystal has a layered perovskite structure, and the layered perovskite structure includes a perovskite structure in which the number of octahedral network of cations and anions of the Group 14 element is 2 or more and 8 or less. With this structure, the compound of this embodiment can be produced at a low temperature, has a large exciton binding energy, and is excellent in thermal stability. In addition, in this embodiment, "excellent in thermal stability" means that the thermal decomposition temperature and/or the thermal decomposition start temperature is higher. Moreover, "the binding energy of excitons is large" can be determined by whether or not exciton absorption is observed at room temperature for the compound.

(Compound)
The compound of the present embodiment is a compound containing a cation and an anion, wherein the cation contains three or more kinds of cations, and 5 mol% or more and 90 mol% or less of the cation is a Group 14 element cation, 5 mol% to 90 mol% of the cation is an organic molecular cation A having 3 to 20 carbon atoms, and 5 mol% to 90 mol% of the cation is a Group 1 element cation and/or carbon It is an organic molecular cation B having a number of 2 or less and a sum of carbon number and nitrogen number of 3 or more and 5 or less. As described above, when the compound contains three or more kinds of cations, it is possible to form a layered perovskite structure including both the layered structure and the structure in which the octahedral network has a plurality of layers. The layered perovskite structure means a crystal structure that is a perovskite structure including at least the layers described below.

From the viewpoint of being more advantageous for forming the octahedral network, the content of Group 14 element cations relative to the total amount of cations contained in the compound (100 mol%; the same applies hereinafter) is 10 mol% or more. It is more preferably 15 mol% or more, still more preferably 30 mol% or more, and particularly preferably 40 mol% or more. In addition, from the viewpoint of further facilitating the formation of the layered structure, the content of the Group 14 element cation with respect to the total amount of cations contained in the compound is preferably 80 mol% or less, and more preferably 75 mol% or less. It is preferably 70% or less, more preferably 65 mol% or less.

The Group 14 element cation is not particularly limited, and examples thereof include Si ⁴⁺ , Ge ²⁺ , Ge ⁴⁺ , Sn ²⁺ , Sn ⁴⁺ , and Pb ²⁺ . From the viewpoint of being more advantageous in forming an octahedral structure of the group 14 element cation and the group 17 element anion, the group 14 element cation is preferably a divalent cation, specifically, Ge ²⁺ , Sn ²⁺ or Pb ²⁺ is preferred. Further, from the viewpoint of being relatively stable against oxidation, the Group 14 element cation is more preferably Sn ²⁺ or Pb ²⁺ , further preferably Pb ²⁺ . In this embodiment, the Group 14 element cation particularly preferably contains at least one of a tin cation and a lead cation, and a tin cation or a lead cation is particularly preferable. The Group 14 element cations may be used alone or in combination of two or more.

In the compound of the present embodiment, the cation includes an organic molecular cation A having 3 to 20 carbon atoms. When the organic molecule cation A has 3 or more and 20 or less carbon atoms, the compound can form a layered structure more effectively and surely. The carbon chain of the organic molecular cation A may include one or more of a straight chain, a branched chain and a cyclic structure. Here, the term “straight chain” includes a carbon chain having no branched chain, and does not include an aromatic ring. From the viewpoint that the organic molecule cation A can be more densely included in the compound, the carbon chain of the organic molecule cation A is preferably only a straight chain. Further, from the viewpoint of being more advantageous to the thermal stability of the organic molecule cation A, the carbon chain of the organic molecule cation A preferably contains an aromatic ring. From the viewpoint of being more advantageous in forming a layered perovskite structure including a structure in which the octahedral network has a plurality of layers, the organic molecule cation A preferably has 4 or more carbon atoms, and more preferably 6 or more carbon atoms. .. On the other hand, the carbon number of the organic molecule cation A is preferably 10 or less, more preferably 8 or less, and further preferably 6 or less, from the viewpoint of being more advantageous in forming the perovskite structure. The organic molecule cation A preferably contains an ammonium cation from the viewpoint of being more advantageous for crystal formation. Further, from the viewpoint of being more advantageous for crystal formation, the number of ammonium cations contained in the organic molecule cation A is preferably 1 or more and 4 or less, more preferably 1 or more and 2 or less, and preferably 1. Most preferred. Specific examples of the organic molecular cation A include, for example, propylammonium, butylammonium, pentylammonium, hexylammonium, heptylammonium, octylammonium, nonanammonium, decanammonium, aniline, propyldiammonium, butyldiammonium, pentyldiammonium. Ammonium, hexyl diammonium, heptyl diammonium, octyl diammonium, nonanediammonium, and decane diammonium, from the viewpoint of being more advantageous for the formation of perovskite structure, propylammonium, butylammonium, pentylammonium, hexylammonium, Butyl diammonium, pentyl diammonium, hexyl diammonium, heptyl diammonium, octyl diammonium, nonanediammonium, and decane diammonium are preferred, and propylammonium, butylammonium, pentylammonium, and hexylammonium are more preferred. The organic molecule cation A may be used alone or in combination of two or more.

The content of the organic molecule cation A with respect to the total amount of cations contained in the compound is preferably 10 mol% or more, more preferably 20 mol% or more, from the viewpoint of being advantageous in forming the layered perovskite structure. It is more preferably 25 mol% or more. The content of the organic molecule cation A is preferably 70 mol% or less, more preferably 60 mol% or less, and 50 mol% or less from the viewpoint of being advantageous in forming more octahedral network structure. Is more preferable.

In the present embodiment, 5 mol% or more and 90 mol% or less of the cations of the compound are group 1 element cations and/or have a carbon number of 2 or less and a sum of carbon number and nitrogen number of 3 or more and 5 or less. It is an organic molecular cation B. The fact that the cation of the compound contains a predetermined amount of Group 1 element cation means that the layered perovskite structure has a structure in which the octahedral network has a plurality of layers, the thermal stability is improved, and the operation stability is improved. Is important from the perspective of improving. In the present embodiment, “excellent in operational stability” means that the phase transition temperature is higher in the range of 0° C. or higher. The excellent operational stability can be evaluated by a differential scanning calorimeter or the like. In addition, the fact that the cation of the compound contains a predetermined amount of the organic molecular cation B having a carbon number of 2 or less and the sum of the carbon number and the nitrogen number of 3 or more and 5 or less means that the compound has a layered perovskite structure to form a multilayer octahedral network. It is important from the viewpoint of including a structure, improving thermal stability, improving crystallinity, and improving c-axis orientation. The cation of the compound may include any one or both of a Group 1 element cation and an organic molecular cation B having a carbon number of 2 or less and a sum of the carbon number and the nitrogen number of 3 or more and 5 or less. From the same viewpoint as described above, the total content thereof is 5 mol% or more, preferably 10 mol% or more, and preferably 14 mol% or more with respect to the total amount of cations contained in the compound. More preferably, it is more preferably 18 mol% or more. The total content thereof is 90 mol% or less, preferably 80 mol% or less, with respect to the total amount of cations contained in the compound, from the viewpoint of being more advantageous for forming the layered improvement of the compound, 70 It is more preferably at most mol%, and even more preferably at most 60 mol%.
The organic molecular cation A and the organic molecular cation B in the present embodiment have different structures.

The content of Group 1 element cations with respect to the total amount of cations contained in the compound is such that the compound contains a multi-layered octahedral network, the thermal stability is improved, the operation stability is improved, and a thin film with small irregularities is formed. From the viewpoint of being more advantageous, it is preferably 10 mol% or more, more preferably 14 mol% or more, and further preferably 18 mol% or more. The content of the Group 1 element cation is preferably 70 mol% or less, more preferably 60 mol% or less, and 50 mol% or less from the viewpoint of being more advantageous in forming the layered structure of the compound. Is more preferable. Specific examples of the Group 1 element cations include sodium cations, potassium cations, rubidium cations, and cesium cations. From the viewpoint that the compound is advantageous in that it includes a structure in which the number of layers of the octahedral network is plural, thermal stability is improved, operation stability is improved, and crystallinity is improved, the Group 1 element cation is , A rubidium cation, or a cesium cation is preferable, and a cesium cation is more preferable. The Group 1 element cations may be used alone or in combination of two or more.

The content of the organic molecule cation B with respect to the total amount of cations contained in the compound is such that the compound contains a multi-layered octahedral network structure, the thermal stability is improved, the operation stability is improved, the crystallinity is improved, and the c-axis direction is increased. From the viewpoint of being advantageous in the formation of the orientation of the solar cells and the improvement of the solar energy conversion of the solar cell light absorption layer, it is preferably 10 mol% or more, more preferably 14 mol% or more, and 18 mol%. It is more preferable that the above is satisfied. The content of the organic molecular cation B is preferably 70 mol% or less, more preferably 60 mol% or less, and 50 mol% or less from the viewpoint of being more advantageous in forming the layered structure of the compound. It is more preferable that there is. In the organic molecule cation B, the sum of the number of carbon atoms and the number of nitrogen atoms is 3 or more and 5 or less, so that thermal stability is improved, operation stability is improved, crystallinity is improved, and orientation in the c-axis direction is formed. It is important from the viewpoint of becoming more advantageous. The sum of the carbon number and the nitrogen number of the organic molecule cation B is 3 or more from the viewpoint of being advantageous due to the improvement of thermal stability, the improvement of operation stability, the improvement of crystallinity, and the formation of orientation in the c-axis direction. It is preferably 4 or less, and more preferably 3. The carbon number of the organic molecular cation B is advantageous for inclusion of a multi-layered octahedral network structure depending on the compound, improvement of thermal stability, improvement of operation stability, improvement of crystallinity, and formation of orientation in the c-axis direction. From a certain viewpoint, 1 is more preferable. The nitrogen number of the organic molecular cation B is preferably 1 or more and 4 or less, more preferably 2 or more and 3 or less, and 2 from the viewpoint of including a multilayer octahedral network structure with a compound. Is more preferable. The organic molecular cation B includes the compound having a structure in which the number of layers of the octahedral network is plural, the thermal stability is improved, the operation stability is improved, the crystallinity is improved, and the orientation in the c-axis direction is performed. From the viewpoint of being more advantageous for formation, it is preferable to include an ammonium cation. Specific examples of the organic molecule cation B include formamidinium cation, acetamidinium cation, and guanidinium cation, and formamidinium cation is particularly preferable. The organic molecular cation B is used alone or in combination of two or more.

The compound contains the group 17 element anion in an amount of 30 mol% or more and 100 mol% or less based on the total amount (100 mol%) of anions contained therein. It is important for the compound to contain the group 17 element anion in an amount of 30 mol% or more and 100 mol% or less to form crystals at low temperatures and improve semiconductor characteristics. When the compound contains different kinds of Group 17 element anions, the content of the Group 17 element anions with respect to the total amount of anions contained in the compound is the sum of their molar ratios. From the viewpoint of being more advantageous in forming crystals at low temperatures and improving semiconductor properties, the content of the Group 17 element anion relative to the total amount of anions contained in the compound is preferably 55 mol% or more, and 65% or more. Is more preferable and 80 mol% or more is further preferable. The specific Group 17 element is not particularly limited, but examples thereof include iodine, bromine, and chlorine. From the viewpoint of being advantageous for crystallization, the Group 17 element preferably contains iodine or bromine. From the viewpoint of further reducing the hand gap, the Group 17 element more preferably contains iodine. From the viewpoint of improving crystallinity, the Group 17 element more preferably contains bromine. The Group 17 elements may be used alone or in combination of two or more.

In this embodiment, the compound has a layered perovskite structure including an octahedral network structure in which a plurality of layers are connected as a crystal structure. Since the compound has such a perovskite structure, it is more advantageous in charge transfer than hexagonal crystals and orthorhombic crystals. The compound having a perovskite structure in the present embodiment is represented by, for example, a general formula of A ^a ₂ A ^b B ₂ X ₇ , and the cations of the A site (A ^a site and A ^b site) and the B site, and the X site Composed of anions. Examples of such a compound include (C ₆ H ₁₃ NH ₃ ) ₂ (CHNHNH ₃ )Pb ₂ I ₇ . In this compound, the cation at the A ^a site is C ₆ H ₁₃ NH ₃ ⁺ , the cation at the A ^b site is CHNHNH ₃ ⁺ , the cation at the B site is Pb ²⁺ , and the cation at the X site is I ⁻ . Correspond. The cation at the B site is bound to the anion at the X site in hexacoordinate, forming an octahedron. At least a part of the octahedron structure shares the vertex with the adjacent octahedron structure. The layered structure in the present embodiment means a structure having an interlayer, and the interlayer means a structure having a face in which an octahedral structure formed by a cation at the B site and an anion at the X site does not share a vertex. The layered perovskite structure means a structure having the layered structure and a planar structure in which the octahedrons are connected (hereinafter, referred to as “octahedral planar structure”). Further, the octahedral network composed of cations and anions of the Group 14 element means a structure in which two or more layers of the octahedral planar structure are overlapped, and for example, five or more of each octahedron share a vertex. .. This crystal structure can be evaluated by various known methods such as X-ray crystal structure analysis and a lattice image of a transmission electron microscope image.

In the perovskite structure of the compound of the present embodiment, A ^a site is an organic molecular cation A, A ^b site is a Group 1 element cation and/or organic molecular cation B, B site is a Group 14 element cation, and X site is a 17th group. It is preferably a group element anion. The interlayer distance of the layered perovskite structure in the compound is preferably 8 Å or more and 40 Å or less from the viewpoint of being advantageous in forming the layered perovskite structure. In the present embodiment, it is preferable that the structure in which the octahedral network included in the layered perovskite structure has a plurality of layers includes a structure in which the octahedral planar structure is overlapped by two or more layers and five or less layers. In order that the binding energy of excitons is larger, the band gap is smaller, and carrier movement is more advantageous, it is preferable that the octahedral planar structure has two or more layers and five or less layers. From the viewpoint of further increasing the binding energy of excitons, in the structure in which the octahedral network included in the layered perovskite structure has a plurality of layers, it is preferable that the octahedral planar structure has four or less overlapping layers, and three or less overlapping layers. It is more preferable that the two layers are overlapped.

A large amount of visible light (>400 nm) is included in sunlight, and it is advantageous that the compound has a small band gap for effective use of sunlight. From such a viewpoint, the band gap of the compound is preferably 3.00 eV or less, and more preferably 2.80 eV or less. On the other hand, from the viewpoint that the photovoltaic power can be made larger, the transmitted light can be used more effectively, and the energy loss due to the emission wavelength when the excitation light having the same wavelength is irradiated is smaller, the band gap of the compound is It is preferably 1.80 eV or higher, more preferably 2.00 eV or higher.

In this embodiment, the higher thermal decomposition temperature and/or higher thermal decomposition start temperature can be evaluated by various known methods, for example, the weight reduction. Further, the thermal decomposition temperature and the thermal decomposition start temperature can be determined as a temperature at which the weight loss is 5% by mass and a temperature at which the weight loss is 1% by mass, respectively.

The compound of this embodiment may take various forms, but it is preferably in the form of a solid powder or a thin film from the viewpoint of easier handling, and in the form of a thin film from the viewpoint of being more advantageous in the laminated structure. Is more preferable.

The crystallite size of the compound is preferably 1 nm or more and 500 nm or less. From the viewpoint of being more advantageous for improving the crystallinity, the crystallite size is more preferably 5 nm or more, further preferably 10 nm or more. The crystallite diameter is preferably 200 nm or less, and more preferably 100 nm or less, from the viewpoint of being more advantageous for forming a thin film having small irregularities.

(Method for producing compound)
The method for producing the compound of the present embodiment is not particularly limited, and for example, it may be carried out by using a predetermined raw material described below and passing through predetermined steps. In particular, from the viewpoint that a structure in which the number of layers of the octahedral network is a plurality of layers under low temperature conditions and a layered perovskite can be produced, the production method is a method for producing a compound, and a compound precursor containing a cation and an anion. And a step of heating the compound precursor at a temperature of 0° C. or higher and 150° C. or lower, wherein the compound precursor has 3 or more kinds of cations and 5 mol% or more of the cations. 90 mol% or less is a Group 14 element cation, 5 mol% or more and 90 mol% or less of the cation is an organic molecular cation A having 3 to 20 carbon atoms, and 5 mol% or more and 90 mol% or less of the cation is A group 1 element cation and/or an organic molecular cation B having a carbon number of 2 or less and a sum of the carbon number and the nitrogen number of 3 or more and 5 or less, and 30 mol% or more and 100 mol% or less of the anion is Group 17 It is an element anion and is a crystal having a layered perovskite structure from the compound precursor by the heating step, and the number of layers of the octahedral network of the group 14 element cation and anion in the layered perovskite structure is 2 or more and 8 layers. The manufacturing method for forming the following structure is preferable. That is, the manufacturing method is a compound containing a cation and an anion, wherein the cation contains three or more kinds of cations, and 5 mol% or more and 90 mol% or less of the cation is a Group 14 element cation, 5 mol% to 90 mol% of the cation is an organic molecular cation A having 3 to 20 carbon atoms, and 5 mol% to 90 mol% of the cation is a group 1 element cation and/or a carbon number. Is an organic molecular cation B having a sum of carbon number and nitrogen number of 2 or less and 3 or more and 5 or less, and 30 mol% or more and 100 mol% or less of the anion is a compound precursor of the Group 17 element, By heating at a temperature of 0° C. or higher and 150° C. or lower, a crystal having a layered perovskite structure and having a layered perovskite structure having two or more layers and eight or less layers of the octahedral network is formed. It is preferable to include the step of It is important for the compound precursor to contain predetermined cations and anions in order to form a layered perovskite structure. In the compound precursor of this embodiment, cations other than the group 14 element cations correspond to so-called counter cations.

As a raw material of the compound of the present embodiment, a substance containing a cation element constituting the compound and a substance containing an anion element constituting the compound are preferable. In particular, in the method for producing the compound of the present embodiment, the step of preparing the compound precursor is a solution containing an aprotic polar solvent, the counter cation, a Group 14 element cation, and a Group 17 element anion. And a step of preparing a solution in which the molar ratio of the group 17 element anion and the group 14 element cation (group 17 element anion/group 14 cation) is 0.1 or more and 10 or less. And removing the solvent from the solution.

Specifically, it is preferable to use a metal halide, a salt of a base and hydrogen halide, or the like as a raw material for the above compound. The halogen species constituting the metal halide is preferably a Group 17 element in the new IUPAC periodic table, and specific Group 17 elements are not particularly limited, and examples thereof include iodine, bromine and chlorine. From the viewpoint of being advantageous for crystallization of the compound, iodine and bromine are preferable. From the viewpoint of reducing the hand gap of the compound, the Group 17 element is more preferably iodine. From the viewpoint of improving crystallinity, the Group 17 element is more preferably bromine. The Group 17 elements may be used alone or in combination of two or more.

Specific examples of the salt of the above base and hydrogen halide include, but are not limited to, formamidine hydrogen chloride, formamidine hydrogen iodide, formamidine hydrogen bromide, acetamidine hydrogen chloride. , Acetamidine/hydrogen iodide, acetamidine/hydrobromide, guanidine/hydrogen chloride, guanidine/hydrogen iodide, guanidine/hydrobromide, etc., formamidine/hydrochloric acid salt, form Amidine/hydrogen iodide salts and formamidine/hydrobromide salts are mentioned, and these are more preferable. The said salt is used individually by 1 type or in combination of 2 or more types.

The compound of the present embodiment can also be produced by a method using no solvent or a method using a solvent. Methods that do not use solvents include, but are not limited to, vapor deposition and solid phase methods. From the viewpoint of producing a compound having a uniform composition, the compound of the present embodiment is produced by a method using a solvent, that is, a method of crystallizing by removing the solvent from a solution in which the above raw materials are dissolved in the solvent. Is preferred. That is, the method for producing a compound according to the present embodiment, a substance containing the above-mentioned predetermined cation and anion, a step of dissolving a solution in an aprotic organic solvent to obtain a solution, and a step of removing the solvent from the solution It is preferable to include. In the above, it is preferable to use an aprotic organic solvent as the solvent from the viewpoint of being advantageous in dissolving the Group 14 element halide, which is a suitable raw material for the compound. Among the aprotic organic solvents, specifically, dimethylformamide (hereinafter referred to as DMF), dimethylsulfoxide, and γ-butyrolactone are preferable, and DMF is more preferable from the viewpoint of being advantageous in forming a compound.

The solution preferably contains a counter cation contained in the compound, a Group 14 element cation, and a Group 17 element anion. The molar ratio of the group 17 element anion and the group 14 element cation (group 17 element cation/group 14 element cation) is preferably 0.1 or more and 10 or less, and 0.5 or more and 8 or less. It is more preferable that it is 1 or more and 5 or less. Particularly preferred is a method for producing a compound, which further comprises a step of removing the solvent from the solution prepared as described above. The step of removing the solvent from the solution is not particularly limited, and examples thereof include a step of removing the solvent by evaporation by heating, and a step of removing the solvent which is a good solvent by contacting or mixing with the poor solvent.

Methods for immobilizing raw materials for producing the compound, for example, a method for producing a compound in a thin film form include, but are not limited to, a spin coating method, a spray method and a liquid phase reaction method using a solution. The spin coating method is preferable from the viewpoint that there is little risk of ignition of the solution and/or the adjustment of the preparation method is easy. From the viewpoint of removing excess solvent and promoting nucleation, it is preferable to use a poor solvent for crystal formation. Examples of the poor solvent include diethyl ether, acetonitrile and toluene.

The atmosphere for producing the compound is not particularly limited and can be prepared, for example, in the air or an inert atmosphere. From the viewpoint of easier preparation, it is preferably prepared in the atmosphere. In addition, it is preferable to prepare the compound in an inert atmosphere from the viewpoint of increasing the purity of the compound.

(Use)
The compound of this embodiment can be used as a semiconductor material. Examples of the semiconductor material in the present embodiment include materials having a band gap of 2 eV or less.

The compound of this embodiment can also be used for other purposes. Specifically, a material that conducts electrons, holes, or ions, a material that utilizes generation of photoexcited carriers by light absorption, and a material that utilizes light emission by recombination thereof can be given. More specifically, examples thereof include a light emitting material, a solar cell material, a solar cell light absorption layer, an optical sensor, a photocatalyst, an ion conductive material, a conductive material, a piezoelectric element, and a power device. The ion in this embodiment refers to a cation or an anion that constitutes the material. From the viewpoint that the binding energy of excitons is larger, the compound is preferably used as a light emitting material. The compound is preferably a compound for the light absorption layer of a solar cell from the viewpoint of being able to absorb light having a wavelength contained in sunlight. Further, the compound is preferably used as an optical sensor from the viewpoint of being able to use light of a specific wavelength.

Since the compound of this embodiment has excellent light emitting characteristics, it is preferably applied to a light emitting device or the like containing the compound. The compound of the present embodiment can be preferably used as a light emitting material in combination with the features that the Stokes shift of light emission can be reduced and the light emission quantum yield can be increased.

The compound of the present embodiment has excellent light absorption properties, and thus is preferably contained in the solar battery cell, and particularly preferably, the light absorption layer provided in the solar battery cell contains the compound. The use of such a compound further improves at least one of photocurrent density, open circuit voltage, and fill factor, thereby improving the solar conversion efficiency in combination with the light absorption property of the compound. be able to.

Hereinafter, the present embodiment will be described more specifically with reference to specific examples and comparative examples. However, the present embodiment is not limited to these examples and comparative examples unless the gist of the present embodiment is exceeded. Absent. Various physical properties and reaction conditions in Examples and Comparative Examples described later were measured and set by the following methods.

(Crystal structure)
The crystal structure of the compound was evaluated from the X-ray diffraction (XRD) pattern by Cu α-ray measured using an X-ray diffractometer (product name “SmartLab”, manufactured by Rigaku Corporation). In particular, whether the structure is a perovskite structure is a diffraction peak at 2θ=14 to 15°, which is derived from the inter-plane diffraction by the Pb cation and the iodine anion in the structure in which the octahedron by the Pb cation and the I anion share a vertex. It was judged by. Further, it is determined whether or not the compound has a layered structure, when the XRD pattern of the compound has a diffraction peak at an angle lower than 2θ=11° (d=8Å), it is determined that the compound has a layered structure. When it did not have a diffraction peak, it was determined that there was no layered structure. The number of octahedral networks formed by group 14 cations and anions was determined to be two layers when the d value of the diffraction peak at the lowest angle was 21 to 25°. The crystallite size was calculated by the Scherrer formula from the half width of the diffraction peak.

(Exciton absorption)
The exciton absorption is evaluated by measuring the absorption spectrum of the compound at room temperature using an ultraviolet-visible near-infrared spectrometer (product name “UV-PC3100”, manufactured by SHIMADZU), and the absorption spectrum has exciton absorption. It was judged whether or not. When it has exciton absorption at room temperature, it means that the binding energy of excitons is large, and when it does not have it, the binding energy of excitons is small.

(Pyrolysis start temperature)
The thermal decomposition start temperature of the compound was determined by thermogravimetric measurement using a differential thermogravimetric simultaneous measurement device (product name “TG-DTA7200”, manufactured by SII Nanotechnology Inc.) at a heating rate of 10 (C/min). The measurement was carried out, and the temperature at which the weight loss was 1% by mass was taken as the thermal decomposition start temperature and the temperature at which the weight loss was 5% by mass was taken as the thermal decomposition temperature.

(Phase transition temperature)
The phase transition temperature of the compound was evaluated by a differential scanning calorimeter (product name “DSC7020”, manufactured by SII Nanotechnology Inc.). The temperature raising rate and the temperature lowering rate were set to 10 (C/min. The lowest phase transition temperature observed at 0° C. or higher was defined as the phase transition temperature.

(Perovskite formation temperature)
The perovskite formation temperature of the compound was the temperature at which the compound having the perovskite structure was formed.

As shown below, the thin films according to Examples 1 to 4 and Comparative Example 1 were prepared and their physical properties were evaluated.

(Example 1)
Using DMF as a solvent, 0.5M hexylamine hydrogen iodide salt, 0.25M formamidine hydrogen iodide salt, and 0.5M lead iodide were dissolved to prepare solution 1. Obtained. A quartz plate was used as a substrate, and 200 μL of the solution 1 was dropped on the substrate. Then, a thin film sample was obtained on the substrate by spin coating at 3000 rpm for 30 seconds and drying. The crystal structure and absorption spectrum of the sample were evaluated. In addition, the sample on the substrate was collected as powder, and thermogravimetric measurement and differential scanning calorimetry were performed. The evaluation results are shown in Table 1.

(Example 2)
Using DMF as a solvent, 0.5M hexylamine/hydrogen iodide salt, 0.25M cesium iodide, and 0.5M lead iodide were dissolved to obtain solution 2. The same operation as in Example 1 was carried out except that Solution 2 was used instead of Solution 1. The evaluation results are shown in Table 1.

(Comparative Example 1)
DMF was used as a solvent, 0.5M hexylamine hydrogen iodide salt, 0.25M methylammonium hydrogen iodide salt, and 0.5M lead iodide were dissolved therein to prepare solution 3. Obtained. The same operation as in Example 1 was performed except that Solution 3 was used instead of Solution 1. The evaluation results are shown in Table 1.

Comparing Examples 1 and 2 with Comparative Example 1, it is understood that all of them are compounds that form a perovskite structure at a low temperature of about 20° C. and are advantageous for charge transfer and the like. The octahedral network formed by the cations and anions of the Group 14 element was two layers in each of Examples 1 and 2 and Comparative Example 1. In addition, since exciton absorption was also observed at room temperature, it can be seen that the compound according to this embodiment can be used as a material having a large binding energy for excitons, which is advantageous as a light emitting material.

Comparing the thermal decomposition start temperature and the thermal decomposition temperature of Examples 1 and 2 and Comparative Example 1, the compounds of Examples 1 and 2 have a higher thermal decomposition temperature than the compound of Comparative Example 1, and the thermal stability is higher. It turns out that it will improve. The order of the thermal decomposition temperatures was (CHNHNH ₃ ) ⁺ :formamidinium>Cs ⁺ >(CH ₃ NH ₃ ) ⁺ :methylammonium. From this, the thermal stability does not depend only on the boiling point of the A ^b site cation having a structure in which the number of layers of the octahedral network is plural, but the steric stability of the formed crystal and the A ^b site cation It can be seen that it depends on the balance of electrostatic stability such as cationicity.

Comparing the phase transition temperatures of Example 2 and Comparative Example 1, it was found that Example 2 relating to the compound of the present embodiment has a high phase transition temperature and is excellent in operational stability.

Comparing Examples 1 and 2 with Comparative Example 1, in Example 1 in which the ^Ab site is an organic molecular cation B having a sum of carbon number and nitrogen number of 3 or more and 5 or less, the crystallite diameter of the perovskite is large. It was found that it was advantageous for improving the crystallinity. Further, it was found that Example 2 in which the ^Ab site is the cation of the first element has a small crystallite diameter, and is advantageous for forming a thin film having small unevenness.

According to the present invention, it is possible to provide a compound which can be produced at a low temperature, has a large exciton binding energy, and is excellent in thermal stability. Therefore, a semiconductor material, more specifically, a light emitting material, a solar cell such as a light absorbing layer of a solar cell, can be provided. It has industrial applicability in fields such as battery materials.

Claims (19)

A compound containing a cation and an anion, wherein the cation contains three or more kinds of cations,
5 mol% to 90 mol% of the cation is a Group 14 element cation,
5 mol% to 90 mol% of the cation is an organic molecular cation A having 3 to 20 carbon atoms,
Below 90 mole% 5 mole% or more of the cation is an alkali metal Kachio down,
30 mol% or more and 100 mol% or less of the anions are Group 17 element anions,
The compound is a crystal, and the crystal has a layered perovskite structure,
A compound comprising a structure in which the number of layers of an octahedral network formed by cations and anions of a Group 14 element in the layered perovskite structure is 2 or more and 8 or less. The compound of claim 1, wherein the organic molecular cation A comprises an ammonium cation. The compound according to claim 1 or 2 , wherein 10 mol% or more and 70 mol% or less of the cation is the Group 1 element cation. The alkali metal cation, a cesium cation, a compound according to any one of claims 1-3. A compound containing a cation and an anion, wherein the cation contains three or more kinds of cations,
5 mol% to 90 mol% of the cation is a Group 14 element cation,
5 mol% or more and 90 mol% or less of the cation is the organic molecule cation A,
5 mol% or more and 90 mol% or less of the cation is the organic molecular cation B,
30 mol% or more and 100 mol% or less of the anions are Group 17 element anions,
The compound is a crystal, and the crystal has a layered perovskite structure,
The layered perovskite structure includes a structure in which the number of layers of an octahedral network formed by group 14 element cations and anions is 2 or more and 8 or less,
The organic molecule cation A is an organic molecule ammonium cation having a carbon number of 3 or more and 20 or less and having one ammonium cation,
The compound, wherein the organic molecular cation B is at least one cation selected from the group consisting of formamidinium cation and acetamidinium cation. The compound according to claim 5 , wherein 10 mol% or more and 70 mol% or less of the cation is the organic molecule cation B. The compound according to any one of claims 1 to 6 , wherein 10 mol% or more and 70 mol% or less of the cation is the organic molecule cation A. The compound according to any one of claims 1 to 7, wherein the organic molecule cation A has 4 to 10 carbon atoms. The carbon chain of the organic molecules cation A is only linear compound according to any one of claims 1-8. The carbon chain of the organic molecules cation A is an aromatic ring, a compound according to any one of claims 1-8. To 70 mol% 10 mol% or more of the cations, the a Group 14 element cationic compound according to any one of claims 1 to 10. The Group 14 element cation, tin cation or lead cation, a compound according to any one of claims 1 to 11. The 100 mol% 55 mol% or more of anionic or less, the a group 17 element anionic compound according to any one of claims 1 to 12. Including the octahedral layer number of the network is three layers or less than the two-layer structure of the layered perovskite structure compound according to any one of claims 1 to 13. A process for the preparation of a compound according to any one of claims 1-14,
Preparing a compound precursor containing the cation and the anion,
Heating the compound precursor at a temperature of 0° C. or higher and 150° C. or lower,
In the compound precursor, the cation contains three or more kinds of cations, 5 mol% to 90 mol% of the cation is a Group 14 element cation, and 5 mol% to 90 mol% of the cation is An organic molecular cation A having 3 to 20 carbon atoms, 5 mol% to 90 mol% of said cation being a Group 1 element cation and/or a formamidinium cation and an acetamidinium cation An organic molecular cation B which is at least one kind of cation selected , and 30 mol% or more and 100 mol% or less of the anion is a Group 17 element anion,
By the heating step, the compound precursor is a crystal having a layered perovskite structure, and the number of layers of the octahedral network of the group 14 element cations and anions in the layered perovskite structure is 2 or more and 8 or less. A manufacturing method of forming a structure. Use as a semiconductor material of a compound according to any one of claims 1-14. Use as a light emitting material of a compound according to any one of claims 1-14. Use as a solar cell material of a compound according to any one of claims 1-14. Use as a light absorbing layer of a solar cell of a compound according to any one of claims 1-14.