Preparation of Reduced Graphene Oxide:ZnO Hybrid Cathode Interlayer Using In Situ Thermal Reduction/Annealing for Interconnecting Nanostructure and Its Effect on Organic Solar Cell

A novel hybrid cathode interlayer (CIL) consisting of reduced graphene oxide and zinc oxide (ZnO) is realized in the inverted organic solar cells (OSCs). A dual nozzle spray coating system and facile one-step in situ thermal reduction/annealing (ITR/ITA) method are introduced to precisely control the components of the CIL, assemble ZnO with graphene oxide, and reduce graphene oxide into in situ thermal reduced graphene oxide (IT-RGO), simultaneously. The ZnO:IT-RGO hybrid CIL shows high electric conductivity, interconnecting nanostructure, and matched energy level, which leads to a significant enhancement in the power conversion efficiency from 6.16% to 8.04% for PTB7:PC71BM and from 8.02% to 9.49% for PTB7-Th:PC71BM-based OSCs, respectively. This newly developed spray-coated ZnO:IT-RGO hybrid CIL based on one-step ITR/ITA treatment has the high potential to provide a facile pathway to fabricate the large-scale, fast fabrication, and high performance OSCs.