The degradation of perovskite solar cells due to reverse bias (RB) is one of the remaining challenges hindering the commercialization of the technology. To overcome this challenge, a thorough understanding of and control over the breakdown (BD) voltage are crucial. A prerequisite for this is that the community “speaks the same language,” that is, that the reported BD voltages are comparable. A review of literature data shows that the impact of measurement parameters is often unknown and seems to depend strongly on sample properties. It follows that standardization is the only way to reach comparability. Here, a set of measurement parameters to fill this gap is proposed. Additionally, various definitions of a “BD voltage” are used in parallel without any way of relating them to each other; this metric and its determination need to be considered as well. After a thorough discussion of the available definitions, the use of the point of maximum curvature is introduced. Its main advantage is the possible connection to an analytical description of the BD mechanism. In this way, a starting point for scientists new to the field of RB stability is provided, and the ground for a broader discussion in the community is prepared.

Among reliability studies on perovskite photovoltaics (PV) cells and modules, partial shading degradation is a crucial and under-investigated topic. In the present work, we use a combination of mapping electroluminescence (EL), photoluminescence (PL), and illuminated lock-in thermography (ILIT) to gain insight into the reverse bias degradation mechanisms induced by partial shading on a monolithically interconnected module. Spatial inhomogeneities across the cell length are shown to play an important role in the degradation. A perovskite module was subjected to partial shading, causing, in the lower region of the shaded cells, a PL signal intensity increase and EL decrease. We suggest the formation of a barrier at one of the perovskite/transport layer interfaces, preventing both carrier extraction in PL and carrier injection in EL. A simple model for the current flow in the presence of the barrier can satisfactorily explain the EL, PL, and ILIT behavior and point to some possible propagation mechanisms. In summary, we show that studying partial shading degradation at module level draws a more complex and realistic picture of the interplay between material and electrical parameters than cell-level studies. We also demonstrate that luminescent and thermal imaging techniques can be combined to draw meaningful conclusions on the degradation mechanisms, their formation, and propagation.

Nonequal current generation in the cells of a photovoltaic module, e.g., due to partial shading, leads to operation in reverse bias. This quickly causes a significant efficiency loss in perovskite solar cells. We report a more quantitative investigation of the reverse bias degradation. Various small reverse biases (negative voltages) were applied for different durations. After normalizing the applied voltages with the breakdown voltages, we found similar dependences of the reverse bias current and the degradation rate. We draw conclusions regarding possible degradation mechanisms and propose a way to increase the comparability of degradation rates for comparing different perovskite solar cells.