Crystallization control of 2.0-eV bandgap perovskites for all-perovskite triple-junction solar cells

Ultrawide-bandgap (UWBG) perovskites are essential for monolithic all-perovskite triple-junction solar cells. However, their performance is limited by severe surface wrinkling, halide heterogeneity and large open-circuit voltage deficits originating from high Br–I ratios. Here we develop a surface reconstruction and halide homogenization strategy that simultaneously regulates crystallization and eliminates stress-induced morphological disorder in 2.0-eV bandgap perovskites. Through synergistic solvent and additive engineering, involving solvent-induced surface reconstruction and transient Cl − incorporation from oleylammonium chloride, surface wrinkling is suppressed, and Br/I crystallization is synchronized with promoted homogeneous halide distribution. The resulting UWBG perovskite films show uniform surface potential, suppressed non-radiative recombination, improved carrier mobility and an open-circuit voltage of 1.46 V. Integrating this UWBG subcell with optimized 1.6- and 1.22-eV absorbers yields monolithic all-perovskite triple-junction solar cells with 30.1% power conversion efficiency (certified 29.3%) and robust operational stability, providing a promising route towards >35% efficient all-perovskite multijunction photovoltaics.