Surface Reconstruction Through Synergetic PEACl‐Modification and Solvent Etching for High‐Efficiency and Stable Perovskite/Silicon Tandem Solar Cells

ABSTRACT Wide‐bandgap perovskite absorbers are essential for constructing efficient perovskite/silicon tandem solar cells, but their device performance is limited by non‐radiative recombination losses, unstable surface phases, and inadequate energy level alignment. In this study, a surface phase regulation strategy is presented that combines PEACl modification with chlorobenzene (CB)/ dimethylsulfoxide (DMSO) mixed solution etching (CDSE) to precisely remove residual PbI 2 and suppress the metastable 2D perovskite phase. The elimination of these parasitic phases enables the remaining PEA + cations to form a 2D phase at grain boundaries (GBs), thereby modulating the electronic environment and aligning the energy levels between the perovskite absorber and the electron transport layer (ETL). This synergistic mechanism substantially reduces interfacial trap states and carrier recombination, resulting in wide‐bandgap perovskite solar cells with a power conversion efficiency (PCE) of 21.77% and excellent operational stability, maintaining 85% of the initial efficiency after 1600 h in an inert atmosphere. Furthermore, when integrated into two‐terminal (2T) mechanically stacked and monolithic perovskite/silicon tandem architectures, the optimized devices achieved efficiencies of 31.85% and 30.17% with enhanced stability. This work, therefore, provides a novel route toward the commercialization of high‐efficiency, stable perovskite/silicon tandem solar cells.