Review: tandem-relevant wide-bandgap perovskites—material systems, evolution pathways, and performance optimization

Wide-bandgap (WBG) perovskites (Eg > 1.67 eV) are key top-cell absorbers for high-efficiency tandem photovoltaics, yet their tandem-relevant development remains constrained by coupled material- and device-level limitations. This review clarifies why tandem-relevant WBG perovskites warrant separate assessment and identifies the principal factors that continue to hinder their practical advancement. This review compares the principal tandem-relevant WBG perovskite material systems, including mixed-halide, all-inorganic, and lead-reduced/lead-free compositions, and examines recent progress through the stage-wise evolution of composition engineering, dimensional engineering, and interface/device engineering. Particular emphasis is placed on structure–property relationships, voltage-loss origins, operational stability, and tandem-oriented benchmark evaluation. Mixed-halide WBG perovskites remain the dominant top-cell platform because of their broad bandgap tunability and high-efficiency potential, but they are also particularly susceptible to phase segregation, ion migration, strain accumulation, and open-circuit voltage (Voc) loss. All-inorganic systems offer stronger intrinsic thermal robustness but continue to face challenges in black-phase stability, crystallization control, and defect suppression, whereas lead-reduced/lead-free systems remain largely exploratory for tandem top-cell applications. Across these material classes, recent progress has depended less on bandgap widening itself than on suppressing non-radiative loss, stabilizing migration- and stress-sensitive regions, and improving tandem integration. Benchmark evaluation has also become increasingly platform-dependent and is now defined more by Voc retention, validation credibility, and application relevance than by champion PCE alone. This review emphasizes that tandem-relevant WBG perovskites should be evaluated not only by nominal bandgap or champion PCE, but also by voltage retention, operational stability, validation credibility, and tandem integration capability. Future advances in tandem-relevant WBG perovskites will depend less on merely positioning the absorber within the target bandgap window than on jointly minimizing voltage loss, preserving operational stability, and enabling scalable tandem integration.