Solar cells based on metal halide perovskites have reached a power conversion efficiency as high as 25%. Their booming efficiency, feasible processability, and good compatibility with large‐scale deposition techniques make perovskite solar cells (PSCs) desirable candidates for next‐generation photovoltaic devices. Despite these advantages, the lifespans of solar cells are far below the industry‐needed 25 years. In fact, numerous PSCs throughout the literature show severely hampered stability under illumination. Herein, several photoinduced degradation mechanisms are discussed. With light radiation, the organic–inorgainc perovskites are prone to phase segregation or chemical decomposition; the oxide electron transport layers (ETLs) tend to introduce new defects at the interface; the commonly used small molecules‐based hole transport layers (HTLs) typically suffer from poor photostability and dopant diffusion during device operation. It has been demonstrated the photoinduced degradation can take place in every functional layer, including the active layer, ETL, HTL, and their interfaces. An overview of these degradation categories is provided in this review, in the hope of encouraging further research and optimization of relevant devices.

The rise of perovskite solar cell performance lies in the increase of fill factor and open-circuit voltage, which depend on high film quality (shunt resistance) and efficient charge transportation (series resistance). Polymer passivation could suppress the film defects, while its poor conductivity leads to a trade-off between passivation quality and series resistance. Here we introduce a polymer network modified mesoporous SnO2 layer to reconcile this contradiction, in which the mesoporous SnO2 was partially coated by the passivation polymer. Electrons can be extracted through the exposed surface of the mesoporous layer, thus realizing high passivation quality and efficient charge transport simultaneously.

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