Photo-homogenization assisted segregation easing technique (PHASET) for highly efficient and stable wide-bandgap perovskite solar cells.

Wide-bandgap (WBG) perovskite solar cells (PSCs) can exceed the Shockley-Queisser limit in tandem solar cells (TSCs), but phase segregation under continuous illumination limits their stability. Using in-situ microscopic characterizations, we investigate the dynamics of photon-induced phase segregation. Initial light soaking drives iodide diffusion into a metastable state, but continued redistribution increases the phase separation energy barrier, resulting in a more stable, segregation-resistant state. Inspired by stabilization methods in silicon photovoltaics, we develop the Photo-Homogenization Assisted Segregation Easing Technique (PHASET), which combines light soaking with 2-ThEABr surface passivation to suppress halide segregation. PHASET enhances efficiency and stability, enabling an efficiency of 20.23% for 1.79 eV WBG-PSCs, with 97% of the initial efficiency retained after 1200 hours of continuous illumination. Integration with a 1.25 eV narrow-bandgap subcell results in a two-terminal all-perovskite TSC with 28.64% efficiency, retaining 77% of its initial performance after 1200 hours of maximum power point tracking.