A Two-Step Top Surface Passivation Strategy for n–i–p Wide-Band Gap Perovskite Solar Cells

Large open-circuit voltage (<i>V</i>_oc) deficit in wide-band gap perovskites has long been an issue that restricts the performance of perovskite-based tandem solar cells. Herein, we proposed a two-step surface passivation (TSP) strategy to enhance the <i>V</i>_oc of the wide-band gap device effectively. A polymer, poly(2-ethyl-2-oxazoline), is used to treat the perovskite top surface to remove impurities and passivate defects, followed by depositing a phenethylammonium salt layer to regulate the energy level alignment between perovskite and adjacent hole transport layer. The TSP strategy effectively suppressed the non-radiative recombination at this interface, increasing the <i>V</i>_oc of the devices by 60 mV in average. The champion 1.68 eV band gap device showed a power conversion efficiency (PCE) of 21.8%, with a <i>V</i>_oc of 1.25 V. Moreover, after aging for 1032 h under ambient conditions, TSP-treated devices retained 86.3% of their initial PCE, while the control samples only remained 72.4% of the initial value.