Imprisoning 2H intermediate phases in blade-coated wide-bandgap perovskites for efficient all-perovskite tandem solar cells

Scalable fabrication of high-efficiency all-perovskite tandem solar cells (TSCs) remains challenging due to notable voltage deficits in wide-bandgap perovskite solar cells, primarily driven by severe halide segregation during the large-scale blade coating process. Here, we introduce 4-aminobenzylphosphonic acid as a functional "2H-imprison" additive that selectively bypasses the formation of the 2H phase (an iodine-rich structure) and promotes the direct crystallization of the desired 3C phase, resulting in a homogeneous phase and halide distribution. Consequently, blade-coated 1.77-electron volt-bandgap perovskite solar cells achieved a power conversion efficiency (PCE) of 20.35% (certified 19.72%) with an open-circuit voltage of 1.35 volts for a ~0.07-square centimeter aperture area, while 1.02-square centimeter devices delivered a PCE of 19.00%. Furthermore, the corresponding blade-coated two- and four-terminal all-perovskite TSCs demonstrated high PCEs of 27.34 and 28.46%, respectively. This study reveals the origins of phase segregation during blade coating and provides a viable strategy to mitigate it, paving the way for scalable and high-efficiency TSCs.