Enhancing device performance of inverted organic solar cells with SnO2/Cs2CO3 as dual electron transport layers

Abstract

Herein, we introduce for the first time that Cs2CO3 can work with SnO2 based on a facile low-temperature solution-processed as dual electron transport layers (ETL) for enhancing device performance of inverted organic solar cells (iOSCs). Aside from better morphologies, a lower work function of ETLs, and an efficient charge extraction, along with a much lower transport resistance at the interfaces are found for iOSCs using SnO2/Cs2CO3 rather than devices based on the SnO2 only. The iOSC devices with P3HT:PC60BM as an active layer, using SnO2/Cs2CO3 (0.5 mg/ml) as dual ETLs, achieved a champion power conversion efficiency (PCE) of 3.75%, which is >36% higher than that of only the based SnO2 (2.75%). Moreover, their PCEs remained at ∼94% of the initial values after storage for 4 weeks in ambient air without any encapsulations, thus demonstrating the excellent long-term device stability. Notably, for the PTB7-Th:PC70BM systems, we also achieved an impressive champion PCE of 7.78% with using SnO2/Cs2CO3 (0.5 mg/ml) as dual ETLs, meanwhile devices based on SnO2 only exhibited a humble PCE of 4.08%. We believe that SnO2/Cs2CO3 dual ETLs concept can also be applied to other optoelectronic devices such as perovskite solar cells or light-emitting diodes, where an ETL is required to ensure high efficiency.