Annealing-Free ZnO:PEI Composite Cathode Interfacial Layer for Efficient Organic Solar Cells

The polymer solar cells owning organic–inorganic composite cathode interlayer are fabricated to achieve well electron extraction compared to the devices with single inorganic semiconductor materials, leading to a significant enhancement of short-circuit current density (J_sc) and fill factor (FF) as well as slight improvement of open-circuit voltage (V_oc). The incorporation of PEI mainly contributes to the decreased work function of the ZnO layer and the reduced interfacial barrier, which are beneficial for the easy electrons extraction and the declined charge recombination. Strikingly, a postannealing treatment is employed for the completed device with electrode to improve the interfacial characteristics between the active layer and the MoO₃ layer, which is a successful method to further increase the V_oc for the device based on PTB7:PC₇₁BM. Our work provides a simple fabrication technology to improve the interfacial contact between active layer and adjacent interlayer, while possessing the major roles on the simultaneously enhanced J_sc, FF, and V_oc.