Wide‐band gap (1.68 eV) perovskite solar cells (PSCs) are important components of perovskite/Si tandem devices. However, the efficiency of wide band gap PSCs has been limited by their huge open‐circuit voltage (Voc) deficit due to non‐radiative recombination. Deep‐level acceptor defects are identified as the major killers of Voc, and they can be effectively improved by passivation with ammonium salts. Theoretical calculation predicts that increasing the distance between F and −NH3+ of fluorinated ammonium can dramatically enhance the electropositivity of −NH3+ terminals, thus providing strong adsorption onto the negatively charged IA and IPb anti‐site defects. Characterizations further confirm that surface gradient passivation employing p‐FPEAI demonstrates the most efficient passivation effect. Consequently, a record‐efficiency of 21.63 % with the smallest Voc deficit of 441 mV is achieved for 1.68 eV‐band gap inverted PSCs. Additionally, a flexible PSC and 1 cm2 opaque device also deliver the highest PCEs of 21.02 % and 19.31 %, respectively.

Due to their excellent thermal stability and ideal bandgap, metal halide inorganic perovskite based solar cells (PSCs) with inverted structure are considered as an excellent choice for perovskite/silicon tandem solar cells. However, the power conversion efficiency (PCE) of inverted inorganic perovskite solar cells (PSCs) still lags far behind that of conventional n–i–p PSCs due to interfacial energy level mismatch and high nonradiative charge recombination. Herein, the performance of inverted PSCs is significantly improved by interfacial engineering of CsPbI3−xBrx films with 2‐mercapto‐1‐methylimidazole (MMI). It is found that the mercapto group can preferably react with the undercoordinated Pb2+ from perovskite by forming Pb–S bonds, which appreciably reduces the surface trap density. Moreover, MMI modification results in a better energy level alignment with the electron‐transporting material, promoting carrier transfer and reducing voltage deficit. The above combination results in an open‐circuit voltage enhancement by 120 mV, yielding a champion PCE of 20.6% for 0.09 cm2 area and 17.3% for 1 cm2 area. Furthermore, the ambient, operational and heat stabilities of inorganic PSCs with MMI modification are also greatly improved. The work demonstrates a simple but effective approach for fabricating highly efficient and stable inverted inorganic PSCs.

The orientation of antimony sulfide (Sb2S3) significantly affects the performance of the Sb2S3 thin film solar cells owing to its intrinsic quasi one-dimensional crystal structure. Producing Sb2S3 film with [hk1]...