Buried modification with tetramethylammonium chloride to enhance the performance of perovskite solar cells with n-i-p structure

Intrinsic defects in the electron transport layer (ETL) and perovskite (PVK) layer, as well as energy level mismatch between the PVK and ETL, severely limit the device performance of perovskite solar cells (PSCs). Here, we introduced a multifunctional molecule (tetramethylammonium chloride, TMACl) as a passivator in the SnO2 ETL. During the annealing treatment, the defects in SnO2 ETL are suppressed by passivating the oxygen vacancies on the surface of SnO2. Moreover, the presence of TMACl enables the defects inevitably generated during the annealing process of PVK to be effectively passivated by the migrating TMA+ cations and Cl- anions. The characterization results further confirm that the surface modification of TMACl is more favorable for the suppression of interfacial recombination and the passivation of bulk and grain boundary defects of PVK compared to the bulk doping method. It is noteworthy that, compared with the pristine device (21.02%), the devices based on TMACl-doped SnO2 and TMACl-modified SnO2 ETLs obtained superior champion efficiencies of 22.71% and 23.08%, respectively. More importantly, the unencapsulated PSCs based on TMACl-modified SnO2 maintained 88% of their original efficiency during 35 days of storage in a humidity-controlled chamber with a relative humidity of 20-30%, demonstrating the passivation of SnO2 ETL using TMACl salts is an effective and promising approach to achieving high photovoltaic performances of PSCs.