Crystallization Modulation and Halide Segregation Suppression in Wide‐Bandgap Perovskite for Efficient All‐Perovskite Tandem Solar Cells

Wide bandgap (WBG) perovskite solar cells (PSCs) play an essential role in tandem solar cell architectures. These architectures represent a promising approach for surpassing the efficiency limits associated with single-junction solar cells. Nevertheless, WBG subcells encounter substantial challenges, particularly those related to inhomogeneous crystallization processes and pronounced non-radiative recombination losses. Additionally, the oxidation of iodide ions during device operation can induce halide segregation, which significantly undermines the operational stability of the devices. In the present study, an effective strategy is introduced through the incorporation of phenylhydrazine derivatives into the perovskite solution. This method simultaneously modulates the crystallization behavior and inhibits iodide oxidation in WBG perovskite. The implementation of this strategy yields high-quality perovskite films and leads to a marked enhancement in the photostability of WBG PSCs. Specifically, inverted single-junction WBG PSCs with a bandgap of 1.77 eV obtained a power conversion efficiency (PCE) of 20.75%, accompanied by exceptional operational stability. Furthermore, by integrating the WBG perovskite subcell with mixed Sn-Pb perovskite subcells, two-terminal all-perovskite tandem solar cells were fabricated, which demonstrated an impressive PCE of 28.63%.