Method for producing a film of light-absorbing material with a perovskite-like structure

Abstract

The invention relates to a method for synthesis of films made of light-absorbing material with perovskite-like structure which can be used for fabrication of perovskite solar cells. The method for synthesis of films made of light-absorbing material with perovskite-like structure with a structural formula ACB.sub.3 is characterized by sequential deposition of a layer of a reagent C onto a layer of a reagent AB with a thickness determined by stoichiometry of the reaction followed by the immersion of the layers in a liquid or gaseous medium containing reagent B.sub.2 where component A states for CH.sub.3NH.sub.3.sup.+, (NH.sub.2).sub.2CH.sup.+, C(NH.sub.2).sub.3.sup.+, Cs.sup.+ or a mixture thereof, component B states for Cl.sup.−, Br.sup.−, I.sup.− or a mixture thereof, component C states for metals Sn, Pb, Bi, or their melts, oxides, salts. The technical result achieved using the claimed invention is a simple and fast method for fabrication of a layer of light-absorbing organic-inorganic material with a perovskite-like structure which is homogeneous due to the formation of a film of the intermediate phase AB-B.sub.2 with improved morphology on the surfaces of a large area due to rapid crystallization, which allows the obtained material to be used in solar cells of large area.

Claims

1. A method for synthesis of films made of light-absorbing material with perovskite-like structure with a structural formula ACB.sub.3, the method comprising: sequentially applying to a substrate a layer of a reagent C and a layer of a reagent AB, and placing the substrate with the applied layers in a liquid or gaseous medium containing reagent B.sub.2 for a period necessary and sufficient for the reaction to complete (C+AB+B.sub.2=ACB.sub.3+X), wherein A is selected from the group consisting of CH.sub.3NH.sub.3.sup.+, (NH.sub.2).sub.2CH.sup.+, C(NH.sub.2).sub.3.sup.+, Cs.sup.+ and a mixture thereof, B is selected from the group consisting of Cl.sup.−, BR.sup.−, I.sup.− and a mixture thereof, C is a metal selected from the group consisting of Sn, Pb, Bi, and a melt, oxide or salt thereof, and X is an optional decomposition product of C if C is in a form of an oxide or a salt.

2. The method as claimed in claim 1, wherein the reagent AB is insoluble in the liquid or gaseous medium and reagent B.sub.2 is soluble in the liquid or gaseous medium.

3. The method as claimed in claim 1 wherein the reagents C and AB are applied per unit area in a stoichiometric amount providing a film with a given thickness.

4. The method as claimed in claim 1 wherein the reagents C and AB are applied by deposition, vacuum deposition, rotating substrate or spraying the solution onto a substrate.

5. The method as claimed in claim 1 wherein C is an oxide or salt and X is removed from the reaction.

6. The method as claimed in claim 1 wherein an excess of B, upon completion of the reaction, is removed by: washing in a solvent, dropping the solvent on the surface, annealing at an elevated temperature, or evaporation under reduced pressure.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The claimed invention is explained with the following drawings and pictures, in particular representing the results of the embodiment of the claimed method for specific compositions.

(2) FIG. 1 shows a scheme of the claimed method for the synthesis of films of light absorbing materials with the composition ACB3.

(3) FIG. 2 shows microphotographs of a film of light-absorbing organic-inorganic perovskite CH.sub.3NH.sub.3PbI.sub.3, obtained according to the claimed method.

(4) The positions on the figures are denoted as following:

(5) 1—substrate

(6) 2—the reagent C deposition

(7) 3—the reagent AB deposition

(8) 4—gaseous medium or a solution containing B.sub.2.

DETAILED DESCRIPTION OF THE INVENTION

(9) The claimed invention can be embodied using known means and methods, including in conditions of industrial production.

(10) Any conductive or non-conductive material or a combination thereof can be used as the substrate. The area and choice of the substrate material can be limited by the requirements of further specific technological steps of the light-absorbing layer formation, however can potentially be arbitrary. Based on the area of the substrate and particular thickness of the film, the required amount of reagents C and AB is determined. To implement the method, a reagent C is deposited onto the selected substrate by known methods. The most optimal is the use of metallic lead, tin or bismuth as C, which are deposited, for example, by vacuum deposition or by electrochemical deposition. In the case of using oxides or salts of the component C, it is also possible to use other methods for forming films in addition to the abovementioned ones, for example, spin-coating, spraying the solution onto a substrate, spray pyrolysis, chemical vapor deposition (CVD), etc. A layer of the component AB is deposited onto a layer of C by means of methods such as sputtering (including vacuum deposition), spin-coating, spraying the solution onto the substrate. Thus, a bilayer film with two sequentially deposited layers C and AB is formed. In order to carry out the reaction of the formation of the film made of the light-absorbing material with a perovskite-like structure, the obtained substrate with deposited layers is immersed in a liquid or gaseous medium, which contains B.sub.2. Dry air, argon, or nitrogen containing iodine vapors (halogens or mixtures thereof) or iodine vapors (halogens or mixtures thereof) without a carrier gas can be used as a gaseous phase; CCl.sub.4, toluene, diethyl ether and other organic solvents containing iodine (halogens or mixtures thereof) can be used as a liquid phase. As a result of the experiments it was established that the optimal characteristics for carrying out the described reaction are performed by iodine vapors with any of the carrier gases or in their absence, as well as solutions of iodine in toluene and CCl.sub.4. The recommended reaction temperature is 0-150° C.

(11) For each specific case, the duration of the process is determined by the rate of the chemical reaction until it is completed. Completeness of the process can be controlled by X-ray phase analysis, etc. At the end of the reaction, the resulting film on the substrate is withdrawn from the chamber containing the medium with the component B.sub.2. The quality of the resulting film is examined by means of electron microscopy used for evaluation of the parameters such as the continuity of the film (the absence of pinholes) and the average size of the crystallites. It was established that the film of the light-absorbing compound CH.sub.3NH.sub.3PbI.sub.3 obtained by the described method has a uniform structure, as seen in FIG. 2, is characterized by the absence of pinholes and an average crystallite size of about 800 nm.

EXAMPLES

(12) Information on the embodiment of the claimed method and the fabrication of a film of a light absorbing compound CH.sub.3NH.sub.3PbI.sub.3 using various components as reagents is provided as examples of particular embodiments.

Example 1

(13) A 60 nm thick layer of lead was deposited by vacuum thermal evaporation on the substrate, consisting of a blocking layer of TiO.sub.2, deposited on a conductive substrate of FTO (fluorinated tin oxide) or ITO (indium doped tin oxide). A MAI layer was then deposited onto the lead layer by vacuum thermal evaporation in the amount corresponding to an equimolar ratio of the amounts of metallic lead and MAI per unit area of the substrate. After that, the substrate with deposited layers was immersed into saturated iodine vapors in argon and held at 40° C. for 10 to 30 minutes. As a result, a layer of perovskite-like structure MAPbI.sub.3 was formed on the substrate. The morphology and phase composition of the film were examined by scanning electron microscopy (FIG. 2) and X-ray phase analysis.

Example 2

(14) A 250 nm thick layer of lead was deposited by vacuum thermal evaporation on the substrate, consisting of a blocking layer of TiO.sub.2, deposited on a conductive substrate of FTO (fluorinated tin oxide) or ITO (indium doped tin oxide). A MAI layer was then deposited onto the lead layer by vacuum thermal evaporation in the amount corresponding to an equimolar ratio of the amounts of metallic lead and MAI per unit area of the substrate. After that, the substrate with deposited layers was immersed in a solution of iodine in CCl.sub.4 with an I.sub.2 content of 10 mg/ml and kept at room temperature for 90 seconds. As a result, a layer of perovskite-like structure MAPbI.sub.3 was formed on the substrate. The morphology and phase composition of the film were examined by scanning electron microscopy and X-ray phase analysis.

Example 3

(15) A 250 nm thick layer of lead was deposited by vacuum thermal evaporation on the substrate, consisting of a blocking layer of TiO.sub.2, deposited on a conductive substrate of FTO (fluorinated tin oxide) or ITO (indium doped tin oxide). A layer consisting of a mixture of MAI and FAI in a molar ratio of 1:1 was then deposited onto the lead layer by vacuum thermal evaporation in the amount corresponding to a molar ratio of 2:1 of the amounts of metallic lead and MAI per unit area of the substrate. After that, the substrate with deposited layers was immersed in a solution of iodine in CCl.sub.4 with an I.sub.2 content of 10 mg/ml and kept at room temperature for 90 seconds. As a result, a layer of perovskite-like structure MA.sub.0.5FA.sub.0.5PbI.sub.3 was formed on the substrate. The morphology and phase composition of the film were examined by scanning electron microscopy and X-ray phase analysis.

(16) Examples of the embodiment of the method with various compounds as reagents are given below.

(17) TABLE-US-00001 TABLE 1 Reaction Average size of C AB B.sub.2 medium Reaction time Phase composition crystallites Uniformity Pb MAI I.sub.2 I.sub.2/argon 3 min MAPbI.sub.3 800 nm No pinholes Pb MAI I.sub.2 I.sub.2/apron 10 min  MAPbI.sub.3 800 nm No pinholes Pb MAI I.sub.2 I.sub.2/CCl.sub.4 1 min MAPbI.sub.3 750 nm No pinholes PbI.sub.2 MAI I.sub.2 I.sub.2/CCl.sub.4 1 min MAPbI.sub.3 900 nm No pinholes Pb MABr I.sub.2 I.sub.2/argon 5 min MAPbBr.sub.xI.sub.3-x 300 nm No pinholes Pb FAI I.sub.2 I.sub.2/CCl.sub.4 1 min FAPbI.sub.3 450 nm No pinholes Pb/Sn MAI I.sub.2 I.sub.2/argon 3 min MAPb.sub.0.9 800 nm No pinholes (9/1) Sn.sub.0.1I.sub.3 PbO.sub.2 MAI I.sub.2 I.sub.2/argon 1 min MAPbI.sub.3 450 nm No pinholes

(18) In the examples described above (Table 1) of the embodiment of the method, highly homogeneous films of a light-absorbing material ACB.sub.3 with a perovskite-like structure were obtained by a method ensuing the possibility of fabrication of the corresponding films of large area.