LAUSR

Abstract SnO 2 with its excellent properties such as high optical transparency, suitable band energy and high electron mobility, recently has received special attention from researchers as an outstanding electron transport layer (ETL) for optoelectronic devices. Here, we demonstrate that SnO 2 combined with ionic liquid (IL), 1-benzyl-3-methylimidazolium chloride ([BzMIM]Cl), based on low-temperature solution-processed can be an excellent ETL for efficient inverted organic solar cells (iOSCs). Our best performance with P3HT:PC 60 BM based iOSCs using SnO 2 /IL as an ETL, has achieved a power conversion efficiency (PCE) of 4.05%, which is the highest reported value so far and was a 38% increase compared to that of SnO 2 only (2.94%). Using ultraviolet photoelectron spectroscopy, we found that the work function of the cathode decreased significantly from − 4.38 eV to − 3.82 eV for SnO 2 /IL, an outstanding feature that is necessary for an ideal ETL. Electrochemical impedance spectroscopy studies revealed a significant lower transport resistance and an efficient charge extraction at the interface between photoactive layer and the electrode for the SnO 2 /IL-based iOSC than for the SnO 2 only device. The iOSC devices using SnO 2 /IL showed excellent long-term stability, with a PCE of ~ 81% compared to the initial value after storage for 2.5 months in ambient conditions. This low-temperature solution-processed SnO 2 /IL is expected for low-cost, high throughput, roll-to-roll process on flexible substrates for iOSC as well as other optoelectronic devices.