LAUSR

Nickel oxide (NiOx) is an attractive hole‐transport material for efficient and stable p–i–n metal‐halide perovskite solar cells (PSCs). However, an undesirable redox reaction occurs at the NiOx/perovskite interface, which results in a low open‐circuit voltage (VOC), instability, and phase separation of the NiOx‐based wide‐bandgap perovskite (Br > 20%). In order to simultaneously address the abovementioned phase separation problem and redox chemistry at the perovskite/NiOx interface, the bandgap is widened from 1.64 to 1.67 eV by adding inorganic CsPbCl3‐clusters (3 mol%) to the Cs22Br15 perovskite precursor solution. Moreover, adding extra 2 mol% CsCl enriches the NiOx/perovskite interface with Cl, thereby preventing the redox reaction at the interface, while controlling the Br content to within 15% improves the photostability of the wide‐bandgap perovskite. Consequently, the power conversion efficiency (PCE) of a single‐junction p–i–n PSC increases from 17.82% to 19.76%, which leads to the fabrication of highly efficient monolithic p–i–n‐type NiOx‐based perovskite/silicon tandem solar cells with PCEs of up to 27.26% (certified PCE: 27.15%). The perovskite to an n–i–p‐type perovskite/silicon tandem solar cell is also applied to deliver a VOC of 1.93 V and a final efficiency of 25.5%. These findings provide critical insight into the fabrication of highly efficient and stable wide‐bandgap perovskites.