Rubidium Induced\nPhase Regulation for High-Performance\nQuasi-2D Perovskite Solar Cells

Quasi-two-dimensional (2D) perovskites are notable for\ntheir diverse\nformulations and environmental stability. However, solution-processed\nquasi-2D perovskites often exhibit inherent multiple-quantum-well\nstructures with broad phase distributions, limiting their efficiency\nin photovoltaic applications. Here, we demonstrate that incorporating\nrubidium ions effectively narrows the phase distribution in quasi-2D\nperovskite by accelerating the formation of the <i>n</i> = 1 2D perovskite phase during the initial crystallization stage.\nThis leads to a decrease in the remaining free organic spacer cations,\nwhich in turn limits the transition to medium-<i>n</i> phases\n(<i>n</i> = 3, 4) and promotes the formation of high-quality\n3D-like or large-<i>n</i> perovskites, ultimately enhancing\ncharge transport of quasi-2D perovskite. Consequently, we achieve\nquasi-2D perovskite solar cells with a champion power conversion efficiency\nof 21.9%. Furthermore, the thermal stability of the unencapsulated\ndevices containing rubidium is significantly improved, with the T80\nlifetime under continuous 60 °C stress increasing from 1150 to\nover 3000 h.