Effect of solution processed salt layers on the device performances of polymer solar cells

We report the solution processed Li salt layers (i.e. LiBF4, and LiTFSI) in poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methylester (PCBM) bulk heterojunction solar cells, which facilitate electron injection at the interface between active layer and Al electrode. The Li salt layers are deposited on top of P3HT:PCBM active layer by simple drop-casting combined with controlled evaporation process. The solar cells employing Li salt layers exhibit the increase of short-circuit current (JSC) and fill factor (FF) by 10% when compared with devices without such an injection layer, resulting in about 28% increase of power conversion efficiency. The effect of Li salt layers on the device performances is investigated with current-voltage (J-V) characteristics and impedance spectroscopy measurements.