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

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.