A Generic Strategy to Stabilize Wide Bandgap Perovskites for Efficient Tandem Solar Cells

Abstract Efficient wide bandgap (WBG) perovskite solar cells (PSCs) are essential for fully maximizing the potential of tandem solar cells. However, these cells currently face challenges such as high photovoltage losses and the presence of phase segregation, which impede the attainment of their expected efficiency and stability. Herein, the root cause of halide segregation is investigated, uncovering a close association with the presence of locally aggregated lead iodide (PbI₂), particularly at the perovskite/C₆₀ interface. Kelvin‐probe atomic force microscopy results indicate that the remaining PbI₂ at the interface leads to potential electrical differences between the domain surface and boundaries, which drives the formation of halide segregation. By reacting the surface PbI₂ residue with ethanediamine dihydroiodide (EDAI₂) at proper temperature, it is possible to effectively mitigate the phase segregation. By applying this surface reaction strategy in WBG inverted cells, a notable improvement of ≈100 mV is achieved in photovoltage over a wide range of WBG cells (1.67–1.78 eV), resulting in a champion efficiency of 23.1% (certified 22.95%) for 1.67 eV cells and 19.7% (certified 18.81%) for 1.75 eV cells. Furthermore, efficiency of 26.1% is demonstrated in a monolithic all‐perovskite tandem cell.