to be connected in series to output larger voltage. Like any classical solar cell, when PSCs are connected in series for largearea modules and panels applications, special attention should be paid to the reverse bias electrical stress of the subcells, because excessive reverse bias due to shading effect (Figure 1a,b) is detrimental to the whole module. In the real environment, external factors such as trees, vegetation, dead leaves, wildlife, snow, and dark clouds will shade some units of the modules from the sun light, leading to the shading effect. For PSCs in modules, the shaded cells can be under reverse bias supplied by the other solar light irradiated cells, [2] as the photocurrent of the illuminated cells can flow to the shaded cells as a reverse current (Figure 1c,d), resulting in power dissipation and subcells thermal degradation that deteriorates the power output of the whole panel. [4][5][6] Joule heat generated in this process will even lead to the local irreversible thermal breakdown of the subcells in the shadow. [7][8][9] At present, however, the reverse bias stability issues of PSCs have not been systematically studied yet. Thus, investigating the phenomenon and mechanism of reverse bias behavior of PSCs, as well as the mechanism of reverse bias breakdown, with anticipating to improve the reverse stability of PSCs, is urgently necessary to promote the commercial application of PSCs.Generally, the overall performance of a solar module and panel depends on the beneficial performance of each individual subcell. Four essential parameters measuring the photovoltaic performance of a solar cell are PCE, FF, V oc , and J sc . In actual testing, these parameters are obtained under forward bias scan, which leads to more attention focusing on the forward bias portion of J-V curve than the reverse bias region. It is worth noting that the investigation of the reverse bias region of J-V curve is equally important, as the p-n junction characteristics of the PSCs is also reflected in their reverse bias behavior. [13][14][15][16][17][18] It has been reported that the reverse current density of classical solar cells (such as Si and CIGS) starts to increase abruptly when the reverse bias voltage is large In recent years, the power conversion efficiencies of halide perovskite solar cells (PSCs) have reached 25.7%. Further commercialization puts forward higher requirements for the stability of PSCs under different stresses. Current research on the stability of PSCs predominantly focuses on investigating the effects of temperature, humidity, oxygen, ultraviolet light, and electrical bias stress, while stability under reverse bias has been poorly studied among the many factors. When large-area application of PSCs panels occurs, the shading effect and local hot spots of PSCs modules in real scenarios all indicate that the research on reverse bias stability of PSCs is urgently needed. Within this review, a bird's-eye view of the recent advances on the reverse bias stability issue and reverse bias behavior of PSCs is obtai...

Perovskite solar cells (PSCs) have shown an impressive power conversion efficiency (PCE) of 26.1%, while their upcoming commercialization urgently needs to solve the stability problem. Among numerous stability issues of PSCs, little attention has been 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. Here, we distinguish the breakdown mechanism dominated by different reverse bias regions of a prototype ETL‐free p‐n junction PSCs. And it is confirmed that PSCs present a thought‐provoking dynamic reverse bias (DRB) behavior and variable reverse breakdown voltage (VRB), which is essentially distinct from classic solar cells. Specifically, VRB is significantly affected by voltage scan rate, range and direction, and illumination. The underlying mechanism was explained by drift‐diffusion modelling 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 VRB and DRB behavior. Predictably, additional obstacles and challenges in the practical application of PSCs will be brought by variable VRB. The module design and bypass diode connection method of PSCs will need to be improved. Moreover, such a newfound DRB behavior can increase the complexity for establishing reliable and non‐destructive VRB measurement procedures of PSCs. So, the understanding of the dynamic process is crucial to establish a standard VRB measurement procedure and further promote the commercialization of PSCs.This article is protected by copyright. All rights reserved.

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