Magnetron sputtered SnO₂ constituting double electron transport layers for efficient PbS quantum dot solar cells

Herein, for the first time, it is successfully demonstrated that radio frequency (RF) magnetron sputtered SnO₂ can be a qualified alternative electron transport layer (ETL) for a high-efficiency PbS quantum dot (QD) solar cell. The highest performing device using such a SnO₂ ETL obtains an efficiency of 8.4%, which is comparable to the sol–gel ZnO-based one (8.8%). The excellent performance mainly results from the improved current density, which is attributed to the superior properties of the SnO₂ ETL, such as high electron mobility and excellent optical transmittance. However, it is also found that the sputtered SnO₂-based devices show smaller voltage and fill factor due to the unsatisfied surface morphology and energy level alignment. By combining a thin (around 10 nm) sol–gel ZnO film on top of a sputtered SnO₂ film to form the double ETL, the best efficiency of 10.1% is obtained, which is the highest efficiency using SnO₂ ETL in a PbS QD solar cell. The work not only provides a new avenue to improve the efficiency of PbS QD solar cells but also offers the possibility to use an industry compatible sputtering technique for PbS QD solar cells.