| Summary: | Mixed lead-tin (Pb:Sn) halide perovskites are promising absorbers withnarrow-bandgaps (1.25–1.4 eV) suitable for high-efficiency all-perovskitetandem solar cells. However, solution processing of optimally thick Pb:Snperovskite films is notoriously difficult in comparison with their neat-Pbcounterparts. This is partly due to the rapid crystallization of Sn-basedperovskites, resulting in films that have a high degree of roughness. Rougherfilms are harder to coat conformally with subsequent layers usingsolution-based processing techniques leading to contact between theabsorber and the top metal electrode in completed devices, resulting in a lossof VOC , fill factor, efficiency, and stability. Herein, this study employs anon-continuous layer of alumina nanoparticles distributed on the surface ofrough Pb:Sn perovskite films. Using this approach, the conformality of thesubsequent electron-transport layer, which is only tens of nanometres inthickness is improved. The overall maximum-power-point-tracked efficiencyimproves by 65% and the steady-state VOC improves by 28%. Application ofthe alumina nanoparticles as an interfacial buffer layer also results in highlyreproducible Pb:Sn solar cell devices while simultaneously improving devicestability at 65 °C under full spectrum simulated solar irradiance. Aged devicesshow a six-fold improvement in stability over pristine Pb:Sn devices,increasing their lifetime to 120 h
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