Impedance Analysis of Thin Films of Organic-Inorganic Perovskites CH(3)NH(3)PbI(3) with Control of Microstructure

The effect of starting reagents (PbI2:{CH(3)NH(3)I + CH(3)NH(3)Cl}) with different ratios in raw solutions on the microstructure of films of organic-inorganic perovskites CH(3)NH(3)PbI(3-x)Cl(x), 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.