Perovskite solar cells (PSCs) have made unprecedented progress in improving power conversion efficiency in the past decade, and they are considered as one of the most promising photovoltaic technologies. However, the commercialization of PSCs still faces significant challenges, such as the stability issue and toxicity of lead. Recently, pursuing ways to alleviate the toxicity of lead has emerged as an attractive research direction in the community of PSCs. In this review, the discussion is on the toxicity of lead and the impact of lead leakage from perovskites to the environment, the recent progress made to reduce the leakage of lead is presented with an emphasis on the lead sequestration materials applied in encapsulation layers and functional layers of PSCs, and the recovery of lead from damaged or decommissioned PSC devices is concisely summarized. This review may serve as a guide for researchers interested in promoting PSCs from exploitation to application.

PCE of PSCs has not yet reached its limit (30.5%), implying there is still much room for further improve the performance of PSCs.To obtain PSCs with higher photoelectric performance and higher stability, various strategies have been developed to optimize the perovskite layer and charge carrier transport layers. [10][11][12] Exploring appropriate materials as efficient electron transport layers (ETLs) is also vital to promote the rapid development of PSCs. Titanium dioxide (TiO 2 ) was initially used as ETL material in PSCs, owing to the advantages of low cost, high stability, and superior ability able to effectively transferring of electrons from the perovskite layer to the bottom electrode. However, the energy levels of TiO 2 and perovskite are not matched well. Meanwhile and the annealing temperature of TiO 2 is high (above 450 °C), which is energy consuming and incompatible with flexible devices. [13][14][15] Alternatively, tin dioxide (SnO 2 ), has become the most commonly used ETL material, due to its advantages of low-temperature manufacturing, good energy level matching, and high electron mobility. However, using SnO 2 as ETL is inevitable to encounter defects (oxygen vacancy defects) pinholes at the film surface. These defects have a significantly negative impact on the photovoltaic performance and stability performance of perovskite solar cells. [16,17] Based on this, interfacial modification and doping strategies were applied to PSCs. Ogomi et al. introduced a monolayer HOCO-R-NH 3

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SnO2-based planar perovskite solar cells (PSCs) are considered as potential photovoltaic candidates due to their simple structures and cost-effective preparation processes. However, the extensive defects accumulated at the buried interface...