Modification of SnO2 buried interface with thiourea to enhance the performance of perovskite solar cells

At present, SnO2 is a widely used material for the electron transport layer in n-i-p perovskite solar cells. However, the SnO2 films prepared by the spin-coating method inevitably generate many defects, especially at the interface. Many strategies have been proposed to passivate the defects of the upper SnO2 interface, but relatively few studies on the SnO2 buried interface. In this study, we introduced thiourea molecules into the SnO2 buried interface. The bottom-up diffusion can effectively passivate the uncoordinated Sn4+ and oxygen vacancies in SnO2 film, benefiting from the passivation of two -NH2 and S atoms with lone pair electrons. In addition, by comparing the different characteristics of SnO2 buried interface modification and the SnO2 doping with thiourea, the two strategies were combined, and the thiourea showed a better passivating effect under this co-processing strategy. Compared with the Control device (19.74%), the device under the co-processing strategy at the optimal concentration exhibits better photovoltaic performance and stability, which obtained the photoelectric conversion efficiency of 21.09% and remained at 88.2% of the initial efficiency after being aged in the air for 60 days without encapsulation. The co-processing strategy provides a valuable reference for the defect passivation of the SnO2 film and its buried interface.