Residual Solvent‐Assisted Surface Reconstruction for Efficient Wide‐Bandgap Perovskite Solar Cells

Abstract Wide‐bandgap (WBG, 1.7–1.8 eV) perovskite solar cells (PSCs) are crucial for fabricating all‐perovskite tandem solar cells (APTSCs), which is the approach to overcome the Shockley‐Queisser limit of single‐junction PSCs. WBG PSCs are still challenged by surface non‐radiative recombination caused by high defect concentration and energy‐level mismatch, which result in large open‐circuit voltage (V OC ) losses. Herein, a residual solvent‐assisted surface reconstruction (RSSR) strategy is introduced by establishing a piperazine/perovskite hybrid surface intermediate phase and recrystallizing this region, which results in an 80 nm thick high‐quality and gradient passivation layer. Moreover, the RSSR strategy creates a bromine compensated and n‐doping surface, which makes a more efficient band alignment and greatly facilitates the surface carrier transport. As a result, the RSSR‐based PSCs achieve an enhancement of V OC from 1.243 to 1.323 V, and of efficiency from 18.00% to 20.39% (certified value of 19.58%), which retains 94% of the initial efficiency after 540 h of continuous 1‐sun light soaking. An efficiency of 28.13% is obtained for the APTSC by employing the RSSR‐based WBG PSCs, showing the great potential in multi‐junction photovoltaics.