Solvated-intermediate-driven surface transformation of lead halide perovskites

The certified quasi-steady-state efficiency of reported inverted perovskite solar cells (PSCs) has rarely surpassed 26%, primarily attributed to interfacial energy-level misalignment and defect-mediated non-radiative recombination. Here we report a surface-phase-transformation strategy of introducing a minuscule amount of N -methyl pyrrolidone (NMP) into the piperazinium diiodide (PDI)-dissolved isopropanol solution to mitigate these challenges. We demonstrate that NMP induces a distinct crystallization pathway on perovskite surfaces during the post-treatment stage, transitioning from a solvated intermediate phase to the α-phase perovskite, bypassing the conventional δ-intermediate-phase → α-phase route, which improves the crystallinity of perovskite surfaces and reduces contact losses. Moreover, NMP enhances the interaction between PDI and perovskites, further optimizing interfacial band alignment. Consequently, we demonstrate high certified power conversion efficiencies of 26.87% (stabilized efficiency), 23.00% and 29.08% for single-junction PSCs, mini-modules and all-perovskite tandems, respectively. Maximum-power-point tracking retains 96% of initial efficiency after 2,500 h under 1-sun illumination at 65 °C in ambient air.