Stability of Wide-Bandgap Perovskites for Tandem Applications: A Review

The bandgap tunability of organic–inorganic hybrid perovskite materials makes them ideal light absorbers in tandem configuration, enabling breakthroughs beyond the theoretical efficiency limit of single-junction solar cells. Representatively, the monolithic perovskite/silicon tandem solar cell has achieved an astounding recorded efficiency of 34.6%. As the top cell absorbers in tandem solar cells, wide-bandgap (WBG) perovskites obtained by on-demand regulation of the iodide–bromine (I–Br) ratio, are responsible for capturing high-energy photons to reduce thermalization losses. However, typical I–Br WBG perovskites suffer severe intrinsic instability, primarily due to halide segregation when exposed to light and/or heat. The instability compromises both the efficiency and durability of tandem devices, posing a major barrier to technology commercialization. In this short review, we first provide a classified overview of recent efforts aimed at inhibiting halogen segregation in WBG perovskites, with a particular focus on the often-overlooked issue of cationic segregation. Furthermore, we highlight that stability could be enhanced by strengthening the interactions between anionic and cationic components and/or employing new constituents in the material formula beyond the I/Br system. Finally, we discuss the primary challenges and offer perspectives on advancing stable WBG perovskites for efficient and stable tandems.