Power Conversion Efficiency Enhancement of Low-BandgapMixed Pb–Sn Perovskite Solar Cells by Improved InterfacialCharge Transfer

The power conversion efficiency (PCE) of low-bandgap mixed Pb–Sn perovskite solar cells (PSCs) has been significantly hindered by large open-circuit voltage (Voc) loss and poor fill factor (FF). Herein, mixed Pb–Sn perovskite films with a composition (FASnI3)0.6(MAPbI3)0.4 were processed with a simple delayed annealing (DA) treatment that enables perovskite films with significantly reduced surface roughness. The treatment reduces nonradiative recombination of interfacial contacts when the perovskite films are interfaced with poly(3,4-ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) and fullerene (C60). Charge transfer at the carrier-collection interfaces has been effectively improved, in agreement with time-resolved photoluminescence (TRPL) and transient photovoltage/photocurrent results. Consequently, the champion cell based on perovskite films with DA treatment shows a high Voc of 0.824 V, indicating a greatly suppressed Voc loss (for a bandgap of ∼1.25 eV), and an overall PCE of over 18.6%.