Potassium chloride passivation for sputtered SnO2 to eliminate hysteresis and enhance the efficiency of perovskite solar cells

In perovskite solar cells (PSCs), tin oxide (SnO2) has been widely used as the electron transport layer (ETL) due to its wide bandgap and high electron mobility. Among the various deposition methods, radio frequency (RF) sputtering offers many advantages for the commercialization of PSCs fabrication. However, conventional PSCs with sputtered SnO2 are subject to severe hysteresis, which occurs owing to defect sites at the ETL-perovskite interface. Further, these defect sites induce non-radiative carrier recombination, causing a decrease in open-circuit voltage and device fill factor. Herein, the surface of RF-sputtered SnO2 was passivated with potassium chloride (KCl) aqueous solution. Through this treatment, it was possible to passivate the defect sites at the interface and change the band alignment for effective electron transport. Thus, a decrease in the trap density of the perovskite led to an increase in efficiency (from 20.9% to 21.9%) and reduction in the hysteresis (from 10.5% to 2.7%) of the PSC. Hence, the KCl passivation process of RF-sputtered SnO2 could be adopted to manufacture hysteresis-free high-efficiency PSCs.