PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT

The organic-inorganic perovskite films CH3NH3PbI3 were synthesized from solutions with different ratios (1:1, 1:2 and 1:3) of initial reagents (PbI2 and CH3NH3I) in a DMF solvent. XRD and Raman spectroscopy shows that the perovskites are formed according to different schemes depending on the ratio of PbI2 and CH3NH3I. At the ratio 1:1 of initial reagents, three intermediate compounds are formed: (CH3NH3)2(DMF)xPbI4, (CH3NH3)2(DMF)2Pb3I8, (CH3NH3)3(DMF)PbI5. At the ratio 1:2 of initial reagents four intermediate compounds are formed: in addition to the above phases, the phase (CH3NH3)2(DMF)2Pb2I6 is found. And at the ratio 1:3 of initial reagents, only two intermediate phases, (CH3NH3)2(DMF)xPbI4 and (CH3NH3)3(DMF)PbI5, are observed. The morphology of the perovskite films was established to depend primarily on the ratio of the initial reagents. The temperature of heat treatment changes only the grain size of films.