RESUMO
The properties of films of organic-inorganic perovskites CH3NH3PbI2.98Cl0.02 depending on the ratio of starting reagents in solutions (PbI2:{CH3NH3I + CH3NH3Cl}) has been investigated. It was found that the formation of the perovskite structure with the ratio of the initial reagents PbI2: CH3NH3I = 1:1 occurs at 70-80 °C, and with the increase of the temperature of thermal treatment to 120 °C, the thermal destruction of the perovskite begins. When the ratio of the starting reagents PbI2: CH3NH3I = 1:2, the formation of the perovskite structure occurs through the intermediate compound (CH3NH3)2PbI4, and when the ratio is 1:3-(CH3NH3)3PbI5 and (CH3NH3)2PbI4. Independent on the ratio of the initial components (CH3NH3I:PbI2), the ratio between the content of lead and iodine in the films remains unchanged, that is why a significant difference in the film properties could be explained by the anisotropy of the particle shape, which is consistent with the data of electron microscopy and X-ray diffractometry.
RESUMO
The effect of starting reagents (PbI2:{CH3NH3I + CH3NH3Cl}) with different ratios in raw solutions on the microstructure of films of organic-inorganic perovskites CH3NH3PbI3-xClx, as well as on the electrical properties, has been investigated. It was found that the crystallinity is increased sharply when the ratio of the starting reagents increases from 1:1 to 1:2 and is changed slightly with a further increase of ratio to 1:3. It is shown that when the ratio of starting reagents varies, the morphology of the films changes; at a ratio of 1:1, the films consist of needle-like particles, and when the ratio is increased, particles become roundish and then faceted. Additionally, the average grain size is decreased. Complex impedance curves and I-V curves have been investigated for samples with different ratios of the starting reagents. With increasing this ratio, the concentration of charge carriers remains unchanged, the mobility of charge carriers decreases, and conductivity passes through a maximum at a ratio of 1:2. The electrical properties of film are the highest at the ratio of starting reagents 1:2 due to the effect of two competing factors: the growth of crystallinity and the decrease of grain size.
