The dissertation is dedicated to the synthesis of films of organic-inorganic compounds CH3NH3PbI3 with the structure of perovskite, the study of their properties depending on the ratio of starting reagents, and solvent, searching ways to increase the stability of organic-inorganic perovskites films, which can be used in the creation of elements for the conversion of solar energy into electricity.
In the dissertation, organic-inorganic perovskites films CH3NH3PbI3 were synthesized by one-step deposition from solutions and films were obtained by spin-coating method. Different ratios of starting reagents PbI2 and CH3NH3I (1:1, 1:2, 1:3) and solvents dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were used for the synthesis of organo-inorganic perovskite films. The peculiarities of the formation of the perovskite structure depending on the ratio of the starting reagents PbI2 and CH3NH3I and the solvent DMF, DMSO has been studied. It was found that when using DMF solvent and different ratio of PbI2:CH3NH3I, organic-inorganic perovskite CH3NH3PbI3 begins to form when processing the film at a temperature of 20-25 °C. When using DMSO perovskite CH3NH3PbI3 begins to form at T = 60 °C for a ratio of 1:1, 1:2 and at T = 70 °C for a ratio of 1:3.
Single-phase perovskite film is not formed at a ratio of starting reagents 1:1, the impurity compound is always present in the film. In all other cases (solvents DMF and DMSO) a single-phase structure of organic-inorganic perovskite of the same chemical composition, but with different morphology, is formed. The temperatures of formation of a single-phase film of organic-inorganic perovskite depend on the ratio of PbI2: CH3NH3I and solvent. It was found that single-phase perovskite films are formed at
115 °C, 170 °C, 175 °C for the ratio of starting reagents 1:1, 1:2, 1:3 in DMF solvent. When using the solvent DMSO single-phase films are formed at 190 °C, 205 °C at a ratio of 1:2, 1:3, respectively.
Depending on the ratio of the starting reagents dissolved in DMF and the heat treatment temperature of the films, the formation of organic-inorganic perovskite occurs through the formation of 3 intermediate compounds (1:1), through the formation of 4 intermediate compounds (1:2), and through the formation of 2 intermediate compounds (1:3). In addition to CH3NH3PbI3 perovskite, other intermediate compounds may be present in the films: (CH3NH3)2(DMF)xPbI4, (CH3NH3)3(DMF)PbI5, (CH3NH3)2(DMF)2Pb2I6 та (CH3NH3)2(DMF)2Pb3I8.
Depending on the ratio of PbI2 and CH3NH3I dissolved in DMSO and the heat treatment temperature, the formation of perovskite CH3NH3PbI3 occurs through the formation of 4 intermediate compounds (CH3NH3)2(DMSO)xPbI4, (CH3NH3)2(DMSO)2Pb3I8, PbI2•2DMSO, PbI2•DMSO.
The structural parameters of organic-inorganic perovskites (unit cell parameters, unit cell volume) are determined. It has been found that as the ratio of starting reagents increases, the unit cell volume for perovskite films increases, which is due to an increase in the amount of solvent included in the structure of perovskite. The unit cell volume for perovskite CH3NH3PbI3 films obtained in the DMSO solvent is smaller than when using DMF. The crystallinity of the films depends on the ratio of the starting reagents, the solvent, and the processing temperature of the film. There are two maxima of crystallinity on the temperature dependence of the crystallinity of the film: the first - due to the contribution of crystalline intermediate compounds and perovskite, the second - due to the contribution of the crystalline phase of perovskite.
