ИСТИНА

Perovskite solar cells represent the most attractive emerging photovoltaic technology, but its practical implementation is limited by low device operational stability. The electric field represents one of the key stress factors leading to fast degradation of perovskite solar cells. To mitigate this issue, one has to gain a deep mechanistic understanding of the perovskite aging pathways associated with the action of electric field. Since degradation processes are spatially heterogeneous, the behavior of perovskite films under applied electric field should be visualized with nanoscale resolution. Herein, we have performed a systematic study of MAPbI3 field-induced degradation using a set of complementary methods including IR s-SNOM, PL-microscopy, confocal microscopy, SEM+EDX, and ToF-SIMS. For the first time, the IR s-SNOM technique was applied to study the nanoscale dynamics of organic cations in the course of the field-induced perovskite degradation process. The obtained results not only enabled high-resolution visualization of the dynamics of CH3NH3+ cations and I- anions in the perovskite film upon bias exposure, but also revealed associated structural and morphological changes originating from the loss of material involved in electrochemical reactions at both cathode an anode. A comparison of SEM+EDX and ToF-SIMS data allowed us to conclude that the final solid product of the field-induced degradation MAPbI3 is metallic lead, which could be formed as a result of further decay of the PbI2 intermediate in the near-cathode area. The obtained results demonstrate that IR s-SNOM represents a powerful technique for studying the spatially-resolved field-induced degradation dynamics of the hybrid perovskite absorbers and identification of more promising materials resistant to the electric field.