Surface Sulfuration of Atomic Layer Deposited Snox for Enhanced Performance of n–i–P Perovskite Solar Cells

Perovskite/silicon tandem solar cells hold great promise for achieving high power conversion efficiencies (PCEs). However, n–i–p tandem devices generally underperform compared to p–i–n configurations, largely due to difficulties in depositing high-quality, conformal electron-transport layers (ETLs) on rough, pyramid-structured silicon surfaces. Atomic layer deposited (ALD)-SnO_x is well suited as an ETL for tandem devices due to its ability to uniformly coat textured surfaces, but its high density of defects significantly limits efficiency compared to conventional solution-processed SnO_x. In this study, an ultrathin evaporated PbS layer is introduced to passivate surface defects in ALD-SnO_x. PbS effectively addresses interfacial defects at the SnO_x/perovskite interface, such as oxygen vacancies and uncoordinated Pb²⁺. Moreover, PbS improves energy-level alignment and lattice matching at the interface, enhancing device performance. With this bridging effect of PbS, a wide-bandgap (1.68 eV) n–i–p single-junction perovskite solar cell achieved a PCE of 20.39% and an open-circuit voltage (V_OC) of 1.22 V, compared to a control device with a PCE of 17.42% and a V_OC of 1.16 V.