Isothiourea-based burial interface modification for high-efficiency and stable perovskite solar cells

Senior oxygen-related defects including O vacancies and dangling O-H bonds in the SnO2 ETL result in non-radiative carrier recombination, which directly affect the efficiency performance and stability of perovskite solar cells. Meanwhile, undercoordinated Pb2+ can also induce non-radiative recombination of photogenerated carriers and provide a pathway for ion migration, leading to further degradation of solar cell performance. To tackle such issues, interface modification with multi-functional small molecules is usually considered a convenient way to inhibit non-radiative recombination and improving carrier transportation. Here, we employ two isothiourea group-based bridge molecule CESC (S-carboxyethyl isothiourea hydrochloride) together with DASC (S-[2-(Dimethylamino) ethyl] isothiourea Dihydrochloride) to passivate the burial interface between SnO2 and perovskite, realizing the dual functional passivation towards both filling O2- vacancy in SnO2 lattice and binding the uncoordinated ions. Perovskite solar cells fabricated with this method shows well-improved optoelectronic performance as well as resistance against ambient moisture. Compared with the control device (17.20%), the efficiency of the devices modified by DASC and CESC increased to 18.75% and 19.04%, respectively. The unpackaged solar cells treated with CESC and DASC maintained 91.2% and 89.5% of their initial efficiency, respectively, after aging for 1000 hours in a high humidity environment.