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.

Quasi-2-dimensional (quasi-2D) perovskite solar cells (PSCs) have attracted much attention due to their superior stability. However, they suffer from inhomogeneous phase distributions and inefficient exciton dissociations, which hinder charge transport and increase energy loss. Herein, a novel chloride-contained aminidium molecule with Lewis-base properties, butyramidinium chloride (BI), was incorporated into quasi-2D PSCs to improve their performance. Chemical interactions between BI and [PbI₆]⁴⁻ octahedra were identified, which optimized the crystallization of 2D perovskite. The resultant film showed a favorable crystal orientation and a homogenized energy landscape with a reduced fraction of low-n 2D phases. Moreover, temperature-dependent photoluminescence results indicate reduced exciton binding energy and enhanced charge dissociation after adding BI. Consequently, quasi-2D PSCs (n = 4) with BI demonstrated a 25% increase in efficiency compared to control devices, attributed to the enhancement of the solar cell’s open-circuit voltage (V_OC) and fill factor. These results underscore the potential of amidinium-based molecules to improve quasi-2D PSC performance.

Enhancing the lifetime of perovskite solar cells (PSCs) is one of the essential challenges for their industrialization. Although the external encapsulation protects the perovskite device from the erosion of moisture and oxygen under various harsh conditions. However, the perovskite devices still undergo static and dynamic thermal stress during thermal and thermal cycling aging, respectively, resulting in irreversible damage to the morphology, component, and phase of stacked materials. Herein, the viscoelastic polymer polyvinyl butyral (PVB) material is designed onto the surface of perovskite films to form flexible interface encapsulation. After PVB interface encapsulation, the surface modulus of perovskite films decreases by nearly 50%, and the interface stress range under the dynamic temperature field (−40 to 85 °C) drops from −42.5 to 64.8 MPa to −14.8 to 5.0 MPa. Besides, PVB forms chemical interactions with FA⁺ cations and Pb²⁺, and the macroscopic residual stress is regulated and defects are reduced of the PVB encapsulated perovskite film. As a result, the optimized device's efficiency increases from 22.21% to 23.11%. Additionally, after 1500 h of thermal treatment (85 °C), 1000 h of damp heat test (85 °C & 85% RH), and 250 cycles of thermal cycling test (−40 to 85 °C), the devices maintain 92.6%, 85.8%, and 96.1% of their initial efficiencies, respectively.