ORGANIC-INORGANIC PEROVSKITE CH3NH3PbI3: MORPHOLOGICAL, STRUCTURAL AND PHOTOELECTROPHYSICAL PROPERTIES

Abstract

The organic-inorganic perovskite films CH3N-H3PbI3 were synthesized from solutions with different ratios of initial reagents (PbI2 to CH3NH3I were taken in the ratio 1:1, 1:2 and 1:3). To deposit films of organic-inorganic perovskite, solutions with different ratio of initial reagents were applied to the substrates by the spin-coating method. The organic-inorganic perovskites synthesized were of one chemical composition in spite of the fact that different chemical reactions proceeded during the synthesis. It was found that the formation of perovskite occurs according to different schemes depending on the ra-tio of PbI2 and CH3NH3I: without the formation of intermediate compounds (at ratio 1:1) and with the formation of one (CH3NH3)2PbI4 (1:2) and two intermediate compounds (CH3NH3)3PbI5, (CH3NH3)2PbI4 (1:3).It was established that regardless of the ratio of the initial reagents, organic-inorganic perovskites with different morphology are formed. At the ratio of the initial reagents 1:1, needle particles formed, and at the ratio of 1:2 and 1:3, particles have the form of a maple leaf and round shape, respectively.To improve the film stability, polyvinyl butyral polymer was used. It is an amorphous colorless pol-ymer which is characterized by high optical properties, environmental (in particular, H2O, O2 and O3) and light resistance. The stability of films of organic-inorganic perovskite without and with a polymer were investigated by XRD, fluorescence spectroscopy and non-contact optical methods. The stability of the films was evaluated by the content of the additional phase of PbI2, which is formed due to the degradation of the organic-inorganic perovskite film CH3NH3PbI3. It was established that the presence of a polymer layer results in improved stability of samples and decrease the rate of surface recombination velocity compared to samples without a polymer layer.The diffusion length of minority charge carriers of the organic-inorganic perovskite films with the polymeric layer was estimated by the method of spectral dependences of the surface photovoltage. The spectra of surface photovoltage and the diffusion length of minority charge carriers of organic-inorganic perovskites with a polymer layer were compared with the literature data for samples without a polymer layer. This comparison shown that the characteristics of the samples with polymer layer are somewhat worse. It is determined that the organic-inorganic perovskite with the polymer layer is characterized by a smaller diffusion length (by 10%) of the minority charge carriers. The prepared perovskite films CH3NH3PbI3 are promising for the development of effective solar cells.