Perovskite solar cells (PSCs) represent a promising next‐generation photovoltaic technology considering their high efficiency and low cost. At the current stage, resolving the stability bottleneck is extremely urgent to realize PSCs’ commercialization since the efficiencies of these cells are improved to a level comparable to that of crystalline silicon solar cells. Similar to other functional layers, a proper choice of the rear electrode atop the perovskite layer is equally important for achieving the device's long‐term stability. This topic has not been comprehensively reviewed before. Here, recent progress in the development of rear electrodes based on metals, carbon‐based materials, transparent conductive oxides, and conductive polymers is summarized, especially focusing on their different impacts on the device's long‐term stability and associated degradation mechanisms. In the context of practical applications, the impacts of rear electrode materials on the device's overall efficiency and cost‐effectiveness are also discussed.

Organic ammonium salts have been widely used for defect passivation to suppress nonradiative charge recombination in perovskite solar cells (PSCs). However, they are prone to form undesirable in-plane favored 2D perovskites with poor charge transport capability that hamper device performance. Herein, the defects passivation role of alkyldiammonium including 1.6-hexamethylenediamine dihydriodide (HDAI 2 ), 1,3-propanediamine dihydriodide (PDAI 2 ), and 1.4-butanediamine dihydriodide (BDAI 2 ) for formamidiniumcesium perovskite is systematically investigated. With help of density functional theory (DFT) calculations, BDA with suitable size can synergistically passivate two defect sites on perovskite surfaces, showing the best defect passivation effect among the above three alkyldiammonium salts. Perovskite films based on BDAI 2 modification are found to keep the 3D perovskite phase with considerably reduced trap-state density, and enhanced carrier extraction. As a result, the BDAI 2 -modified devices deliver impressive efficiencies of 23.1% and 20.9% for inverted PSCs on the rigid and flexible substrates, respectively. Moreover, the corresponding encapsulated rigid devices maintain 92% of the initial efficiency after operating under continuous 1-sun illumination with the maximum power point tracking for 1000 h. Furthermore, the mechanical flexibility of the BDAI 2 -modified flexible device is also improved due to the release of residual stress.

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