Stability Challenges and Solutions in Wide‐ and Narrow‐Bandgap Perovskites for All‐Perovskite Tandem Solar Cells

Abstract Perovskites possess exceptional optoelectronic properties, including tunable direct bandgaps and long carrier diffusion lengths that render ideal absorbers for tandem solar cell architectures. In all‐perovskite tandem solar cells (APTSCs), the integration of wide‐bandgap (WBG) and narrow‐bandgap (NBG) sub‐cells enables more efficient harvesting of the solar spectrum, leading to certified power conversion efficiencies (PCEs) as high as 30.1%. Despite this progress, ensuring long‐term operational stability remains a major challenge. WBG perovskites are prone to photo‐induced phase segregation and the formation of deep‐level defects, whereas NBG perovskites are vulnerable to Sn 2 ⁺ oxidation and asynchronous crystallization‐based defects. These intrinsic instabilities, compounded by extrinsic stressors such as light, heat, moisture, and oxygen, accelerate performance degradation under practical operating conditions. Achieving durable APTSCs thus requires a comprehensive understanding of degradation mechanisms affecting both WBG and NBG absorbers. This review systematically explores both intrinsic and extrinsic degradation pathways in WBG and NBG perovskites, with particular emphasis on the roles of interfaces, charge‐selective layers, and environmental conditions. Furthermore, we summarize recent advances in mitigation strategies aimed at enhancing the stability of APTSCs.