Power Conversion Efficiency Enhancement of Low-Bandgap Mixed Pb-Sn Perovskite Solar Cells by Improved Interfacial Charge 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 (V-oc) loss and poor fill factor (FF). Herein, mixed Pb-Sn perovskite films with a composition (FASnI(3))(0.6) (MAPbI(3))(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 (C-60). 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 V-oc of 0.824 V, indicating a greatly suppressed V-oc loss (for a bandgap of similar to 1.25 eV), and an overall PCE of over 18.6%.