Boosted charge extraction of SnO2 nanorod arrays via nanostructural and surface chemical engineering for efficient and stable perovskite solar cells

Vertically aligned one-dimensional nanorod arrays (NRAs) show great potential as electron transport layers (ETLs) for perovskite solar cells (PSCs) because of the unique characteristic which could realize the directional charge transport and enhanced charge collection. However, the severe charge recombination at the heterointerface between the NRAs ETL and perovskite layer often leads to the unsatisfactory power conversion efficiency (PCE). Here, we remarkably boost the performance of SnO2 NRAs ETL through microstructural and surface chemical engineering. First, the longitudinal size of NRAs is adjusted to alleviate the charge accumulation at the heterointerface. Next, the surface affinity of SnO2 NRAs is improved by thiourea sulfuration for a better penetration of perovskite precursor. More importantly, the strong interaction between the sulfur and the uncoordinated Pb2+ effectively passivate the buried interfacial defects of perovskite layer. Surface sulfuration reconstructs the gradient energy level and promotes the interfacial electron transfer between the ETL and the perovskite layer. As a result, a record PCE of 20.18 % is achieved for the S-SnO2 NRAs based PSCs till now. Meanwhile, the operational stability of the device is enhanced especially in the near-ultraviolet region, which maintains above 80 % of the initial PCE after 72 h of continuous irradiation under ultraviolet light.