Defect engineering for highly efficient and stable perovskite top cells for Si tandems

Abstract Tandem solar cells have emerged as a promising next‐generation photovoltaic technology capable of surpassing the Shockley–Queisser limit of single‐junction devices. In particular, perovskite/Si tandem architectures employing wide‐bandgap perovskites as top absorbers have demonstrated certified power conversion efficiencies approaching 35%, owing to their exceptional bandgap tunability and high achievable open‐circuit voltages. These remarkable advances have been enabled by passivation of various defects in wide‐bandgap perovskites, thereby reducing non‐radiative recombination losses and halide segregation‐related stability issues. This review focuses on recent progress in defect passivation strategies for wide‐bandgap perovskites, as well as earlier studies that established key milestones for state‐of‐the‐art tandem devices. Defect passivation strategies are systematically discussed according to defect location: (i) bulk passivation using additives that enlarge grain sizes, coordinate with detrimental point defects via functional groups, and passivate grain boundaries; (ii) surface passivation by inorganic insulators (e.g., LiF) and molecular passivators; (iii) buried interface passivation via functional self‐assembled monolayers and modulated inorganic interlayers. Particular emphasis is placed on elucidating the relationships between defect‐induced recombination losses, ion migration, and device performance and stability. By critically summarizing recent advances in defect engineering approaches, this review highlights current research trends and key considerations for realizing highly efficient and stable perovskite/Si tandem solar cells.