Phase segregation mechanism and suppression in wide-bandgap perovskites toward efficient and stable perovskite/silicon tandem solar cells

Perovskite solar cells (PSCs) have attracted extensive attention as a new generation of high-efficiency photovoltaic devices owing to their excellent optoelectronic properties and simple fabrication processes. However, the efficiency of single-junction solar cells is constrained by the Shockley-Queisser (S-Q) limit, and further efficiency improvement is gradually approaching a bottleneck. To overcome this limitation, tandem solar cells (TSCs) have been proposed. Among them, perovskite/silicon tandem solar cells (PSTSCs) have emerged as one of the most promising candidates for commercialization by combining the high light-absorption capability of wide-bandgap (WBG) perovskites with the long-term stability of silicon solar cells. Despite these advantages, WBG perovskites remain vulnerable to halide phase segregation when subjected to typical operational stresses, including continuous illumination, elevated temperatures, and internal electric fields. Such compositional instability gives rise to localized bandgap variations and a higher density of defect states, which, taken together, undermine both the power conversion efficiency (PCE) and the operational stability of tandem devices. As a consequence, the ability to effectively regulate and suppress phase segregation in WBG perovskites has become a critical issue in the development of PSTSCs that combine high efficiency with long-term durability. In response to this issue, the present review outlines recent progress in phase-segregation regulation within PSTSCs, with first attention given to the underlying mechanisms responsible for phase segregation in WBG perovskites and its influence on device performance. Subsequently, it deeply explores the mechanism and application effects of optimization strategies involving composition engineering, interface engineering, and additive engineering. Finally, the key mechanisms and practical approaches for suppressing phase segregation in WBG perovskites are summarized, and perspectives are offered on future efforts aimed at further inhibiting perovskite phase segregation for high-efficiency and stable PSTSCs.