Inorganic lead (Pb)-free Cs2AgBiBr6 double perovskite is one of the most promising light absorbers in perovskite solar cells (PSCs) to solve the instability and Pb toxicity problems of organic–inorganic perovskites. However, the intrinsic and extrinsic defects of Cs2AgBiBr6 films strongly limit the power conversion efficiencies (PCEs) of Cs2AgBiBr6-based PSCs. Herein, the first investigation of additive engineering in Cs2AgBiBr6-based PSCs is reported to achieve an outstanding efficiency. The introduction of guanidinium thiocyanate (GuaSCN) additive effectively controls the nucleation of Cs2AgBiBr6 crystals during the film formation process, improves the perovskite film quality, suppresses the charge carrier recombination, and accelerates the charge extraction simultaneously. Consequently, after optimizing the GuaSCN amount, the device shows a stable PCE of 3.02% under maximum power point tracking (MPPT) condition. Furthermore, the introduction of GuaSCN additive remarkably improves the ambient stability of the devices. This work provides insights on additive engineering for enhancing the efficiency and stability of inorganic Pb-free Cs2AgBiBr6-based PSCs toward future industrialization of this technology.

Organic–inorganic perovskite solar cells (PSCs) have delivered the highest power conversion efficiency (PCE) of 25.7% currently, but they are unfortunately limited by several key issues, such as inferior humid and thermal stability, significantly retarding their widespread application. To tackle the instability issue, all-inorganic PSCs have attracted increasing interest due to superior structural, humid and high-temperature stability to their organic–inorganic counterparts. Nevertheless, all-inorganic PSCs with typical CsPbIBr2 perovskite as light absorbers suffer from much inferior PCEs to those of organic–inorganic PSCs. Functional doping is regarded as a simple and useful strategy to improve the PCEs of CsPbIBr2-based all-inorganic PSCs. Herein, we report a monovalent copper cation (Cu+)-doping strategy to boost the performance of CsPbIBr2-based PSCs by increasing the grain sizes and improving the CsPbIBr2 film quality, reducing the defect density, inhibiting the carrier recombination and constructing proper energy level alignment. Consequently, the device with optimized Cu+-doping concentration generates a much better PCE of 9.11% than the pristine cell (7.24%). Moreover, the Cu+ doping also remarkably enhances the humid and thermal durability of CsPbIBr2-based PSCs with suppressed hysteresis. The current study provides a simple and useful strategy to enhance the PCE and the durability of CsPbIBr2-based PSCs, which can promote the practical application of perovskite photovoltaics.