Surface Band Bending Influences the Open-Circuit Voltage of Perovskite Solar Cells

With perovskite solar efficiencies exceeding 23%, more investigations are needed to understand and enhance the open-circuit voltage (V_oc) for further efficiency gains. Here, by changing the perovskite film annealing conditions, we achieve significant V_oc variations in a p–i–n cell architecture. While the morphology remains unaffected, we observe that the annealing conditions affect the surface stoichiometry. Subsequent variations in the V_oc are identified to be caused by differences in trap-assisted recombination processes as well as also largely by the suppression of charge collection due to surface band bending. These findings highlight the impact of surface band bending on V_oc which can be permanently introduced by normal annealing treatments and impede the charge transport process. Our study suggests that the detailed states of the band bending in perovskite films should be carefully examined and designed to maximize the V_oc and consecutively improve the performance of perovskite solar cells.