Phase-Stable Wide-Bandgap Perovskites with 2D/3D Structure for All-Perovskite Tandem Solar Cells

All-perovskite tandem solar cells have exhibited greater potential in achieving power conversion efficiencies that are higher than those of single-junction devices. However, commonly used I/Br mixed wide-bandgap (WBG) perovskites, as an important component in the tandem device, always show a photoinduced halide phase segregation, which results in a large open-circuit voltage deficit and low photostability of the final all-perovskite tandem solar cells. In this work, we successfully stabilized the phase of the WBG perovskite by constructing a 2D wrapped 3D structure via introducing larger organic cation 2-(4-fluorophenyl)ethylamine hydroiodide, which has a high activation energy of ion migration to suppress the halide phase segregation. The phase-stable WBG perovskite solar cells achieved a high open-circuit voltage of 1.35 V with a power conversion efficiency of 19.4% and retain 92.1% of their initial value after 500 h of AM1.5G illumination. Finally, the constructed all-perovskite tandem solar cells achieved a high efficiency of 27%.