Abnormal Dynamic Reverse Bias Behavior and Variable Reverse Breakdown Voltage of ETL-free Perovskite Solar Cells

Perovskite solar cells (PSCs) have shown an impressive power conversion efficiency of 26.1%, while their upcoming commercialization urgently needs to solve the stability problem. Among numerous stability issues of PSCs, little attention is paid to reverse bias stability. When some cells of the module are shaded by irresistible factors, this will cause the current of the illuminated part to flow through the shaded cells as a reverse current and force them to be under reverse bias. Herein, the breakdown mechanism dominated by different reverse bias regions of a prototype electron transport layer free PSCs is distinguished. And, it is confirmed that PSCs present a thought-provoking dynamic reverse bias (DRB) behavior and variable reverse breakdown voltage (V_RB), which is essentially distinct from classic solar cells. Specifically, V_RB is significantly affected by voltage scan rate, range and direction, and illumination. The underlying mechanism is explained by drift-diffusion modeling taking into account the electric field generated by directional ion migration. The latter can hinder the movement of charge carriers and cause the observed variable V_RB and DRB behavior. Predictably, the understanding of the dynamic process is crucial to establish a standard V_RB measurement procedure and further promote the commercialization of PSCs.