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Perovskite solar cells (PSCs) have become a promising candidate for the next‐generation photovoltaic technologies. As an essential element for high‐efficiency PSCs however, the heavy metal Pb is soluble in water, causing a serious threat to the environment and human health. Due to the weak ionic bonding in three‐dimensional (3D) perovskites, drastic structure decomposition occurs when immersing the perovskite film in water, which accelerates the Pb leakage. By introducing the chemically stable Dion‐Jacobson (DJ) 2D perovskite at the 3D perovskite surface, the film dissolution is significantly slowed down, which retards lead leakage. As a result, the Pb contamination is dramatically reduced under various extreme conditions. In addition, the PSCs device deliver a power conversion efficiency (PCE) of 23.6 % and retain over 95 % of their initial PCE after the maximum power point tracking for over 1100 h. [ABSTRACT FROM AUTHOR]

Defects formed at the surface, buried interface and grain boundaries (GB) of CsPbI 3 perovskite films considerably limit photovoltaic performance. Such defects could be passivated effectively by the most prevalent post modification strategy without compromising the photoelectric properties of perovskite films, but it is still a great challenge to make this strategy comprehensive to different defects spatially distributed throughout the films. Herein, a spatially selective defect management (SSDM) strategy is developed to roundly passivate various defects at different locations within the perovskite film by a facile one-step treatment procedure using a piperazine-1,4-diium tetrafluoroborate (PZD(BF 4) 2) solution. The small-size PZD2+ cations could penetrate into the film interior and even make it all the way to the buried interface of CsPbI 3 perovskite films, while the BF 4 − anions, with largely different properties from I− anions, mainly anchor on the film surface. Consequently, virtually all the defects at the surface, buried interface and grain boundaries of CsPbI 3 perovskite films are effectively healed, leading to significantly improved film quality, enhanced phase stability, optimized energy level alignment and promoted carrier transport. With these films, the fabricated CsPbI 3 PSCs based on carbon electrode (C-PSCs) achieve an efficiency of 18.27%, which is among the highest-reported values for inorganic C-PSCs, and stability of 500 h at 85 °C with 65% efficiency maintenance. [ABSTRACT FROM AUTHOR]

• The drop-casting method was for the first time developed to deposit CsPbI 3 films. • A vacuum process was exploited to greatly suppress coffee ring effect (CRE). • The carbon-based CsPbI 3 PSCs achieves a new record efficiency of 16.33 %. • A large-area perovskite film with excellent uniformity is prepared by VA. Inorganic CsPbI 3 perovskite has shown much promise as a light absorber in perovskite solar cells (PSCs) due to its appropriate optical bandgap and high chemical stability. However, it is still a great challenge to deposit large-area CsPbI 3 perovskite films by existing methods (e.g. spin coating). Herein, a facile and scalable strategy based on a drop-casting process is developed. To mitigate the coffee ring effect (CRE) that commonly occurs during drop casting, a vacuum-assisted (VA) process is exploited to boost solvent extraction, which significantly reduces the difference in solvent evaporation rates at the edge and middle regions of droplets. As a result, uniform CsPbI 3 perovskite films with higher crystallinity and lower defect density are deposited by drop casting. By using the CsPbI 3 perovskite film as a light absorber, the carbon-based CsPbI 3 PSCs without hole transport layer achieves an efficiency of 16.33 %, a new record for inorganic C-PSCs. After finely controlling deposition processes, a large-area CsPbI 3 perovskite film (5 × 5 cm2) with excellent uniformity can be easily prepared by the drop casting method. [ABSTRACT FROM AUTHOR]