Activating Halogen Circulation Enables Efficient and Stable Wide‐Bandgap Mixed‐Halide Perovskite Solar Cells

Developing strategies to manage ion-migration-induced phase segregation in wide-bandgap (WBG) perovskites is crucial for achieving high-performance perovskite-silicon tandem solar cells (TSCs). However, maintaining continuous suppression of phase segregation from the film crystallization process to device operation remains a significant challenge. The present study demonstrates an efficient strategy of activating halogen circulation in WBG perovskite by using halogen circulation agents (HCA) of N-halosuccinimide molecules as the sustainable stabilizers, in order to achieve dynamic halogen equilibrium within the precursor solution and perovskite film, which blocks the migration path of Br-/I- ions both in crystallization and aging of WBG perovskites. Attempts on in situ dynamic monitoring of halide migration visually verified the enhanced stability by activated halogen circulation in both WBG films and devices. Consequently, present work achieves a champion efficiency up to 23.25% with a low Voc loss of 0.39 V in the 1.67-eV-bandgap device, and the HCA-based devices can maintain 88% and 93% of their initial efficiencies over 1000 h under continuous illumination and 2500 h at 85 °C in N2 atmosphere, respectively. As a proof of concept, the perovskite/silicon monolithic TSCs are fabricated to demonstrate a high Voc of 1.99 V and a high power conversion efficiency of 33.2%.