ИСТИНА

Perovskite solar cells (PSC) demonstrated impressive power conversion efficiencies going beyond 22%. However, very poor operational stability of these devices hampers significantly their practical application. In particular, perovskites represent solid-state redox active ionic conductors, which might undergo electrochemical degradation if electric bias is applied to the films. Obviously, the active layer of the operating solar cells has to sustain the electric fields induced by the built-in and light-induced potentials. Otherwise, the electrochemical degradation of the active layer material under the solar cell operation conditions would ruin the device performance. In this work, we report a systematic comparative study of the electrochemical stability of a series of hybrid and all-inorganic lead halide based perovskite materials - MAPbI3, MAPbBr3, FAPbI3, FAPbBr3, CsPbBr3, CsPbI2Br. Thin films of these materials were exposed to the potentiostatic polarization under anoxic conditions using the lateral and vertical two-electrode device architectures (electric fields of ~0.1 to 1 mV/nm). We have shown that polarization leads to the appearance of the field-induced gradients in the chemical composition of the films. Additionally, significant changes of the film morphology and the surface potential have been revealed using Kelvin probe force microscopy (KPFM). The analysis of the obtained data allowed us to draw some important correlations between the chemical composition of the perovskite materials and their electrochemical stability, which might guide further design of stable light absorbers for future generation photovoltaics.