Developing wide-bandgap perovskites for tandem solar cells: Challenges and opportunities

Perovskite solar cells stand out due to their excellent optoelectronic properties, relatively simple fabrication methods, and tunable bandgaps. Consequently, their wide-bandgap variants (1.65–2.0 eV) are particularly well-suited for use as top cells in tandem solar cell configurations. However, their development remains hindered by certain challenges, such as halide segregation and high defect density. While previous reviews have summarized advances in this field, there is a lack of a comprehensive discussion that spans from challenges to development and applications. This article, from the perspectives of material and process optimization, specifically focuses on the latest breakthroughs achieved over the past year. It systematically outlines strategies, including additive engineering, crystallization kinetics regulation, and interface engineering, to realize defect passivation, film quality improvement, and device performance enhancement. This review not only delves into the mechanistic understanding of halide segregation but also analyzes recent research progress on the integration of wide-bandgap perovskite top cells with various bottom cells, such as copper indium gallium selenide, silicon, narrow-bandgap perovskites, and organic solar cells. Finally, it highlights future research directions, emphasizing that addressing the intrinsic stability of materials and clarifying the microscopic mechanisms of phase segregation are crucial for advancing their industrial applications.