Defect Passivation of Low-Temperature-Sputtered Tin Oxide Electron Transport Layers Through Magnesium Doping for Perovskite Solar Cells

The optimal choice of electron transporting materials is of vital importance in improving the efficiency and reducing the cost of perovskite solar cells (PSCs) as electron transport layers (ETLs) play a key role in charge extraction and transfer. Despite SnO2 being a commonly used ETL, magnetron-sputtered SnO2 continues to be constrained by oxygen vacancy (VO)-related point defects, which result in severe interface charge recombination, thereby limiting the open-circuit voltage and fill factor of PSCs using magnetron-sputtered SnO2 ETLs. Herein, a doping strategy was adopted to suppress the defect density in magnetron-sputtered SnO2, in which Mg:SnO2 (MTO) was prepared by magnetron co-sputtering of MgO and SnO2 at room temperature. After Mg doping, the VO defects were passivated, the density of the trap states in the SnO2 ETL was reduced, and the energy level alignment between the ETL and perovskite layer was optimized. As a result, the undesired charge recombination was effectively suppressed, thus leading to an approximately 8.7% increase in the average device efficiency and approximately 11% increase in the stabilized power output. The best-performing device achieved an efficiency of 19.55%, therefore indicating the high of the ETL toward the commercialization of PSCs.