Impact of ZnO Photoluminescence on Organic Photovoltaic Performance

ZnO is a widely used electron transport material in third generation solar cells. Intrinsic defects arising from different synthetic methods and conditions lead to different fluorescent colors. The defect mechanisms have been explored in the literature, but their impact on organic photovoltaic (OPV) cell performance is rarely reported. Herein, three different ZnO nanoparticles showing blue, green, and yellow emission colors are synthesized and incorporated into OPV cells. The as-cast ZnO films result in vastly different OPV performances. It is found the sodium acetate as the byproduct of the synthesis can significantly influence the interfacial contact. After removing the impurity via rinsing with polar organic solvents, the different ZnO nanoparticles can deliver similar power conversion efficiencies (PCEs) in three representative OPV systems. The PCEs reached 4, 8, and 10% in P3HT:PC61BM-, PTB7-Th:PC71BM-, and PBDB-T-SF:IT-4F-based OPV cells, respectively. A series of characterizations indicate that the intrinsic defect types do not affect the optical and electrical properties of the ZnO film, including photon transmittance, electrical conductivity, and charge extraction from the active layer as well as electron mobility. The results together suggest that the intrinsic defect in ZnO nanoparticles has little impact on OPV performance. Thus, it might be necessary to revisit the strategies for defect engineering or passivation in oxide-based interfacial materials.