Plasmonic enhancement in PTB7-Th:PC71BM organic photovoltaics

Abstract

Organic photovoltaics struggles with limited exciton diffusion rate and low light absorption rates. The trade-off between these deficiencies limits the thickness of the active layer around 100–200 nm range. Plasmonic light management was introduced as one of the solutions to these problems in the last decade. The plasmonic metal nanostructures can manipulate light in subwavelength regime such as thin-film organic photovoltaics. In this work, we introduced a controllable and reproducible method to incorporate quasi-hexagonal arrays of Au nanostructure on the electron transport layer (ETL), which can directly facilitate light management in the active layer. The inverted PTB7-Th:PC71BM OPVs were selected as the model system, and Au nanostructure arrays were introduced in selected interfaces. In order to match the work function of Au nanostructures and the LUMO level of the PC71BM fullerene component of the bulk heterojunction, PEI was utilized to modify the work function of such surfaces. The plasmon-enhanced inverted OPV devices showed up to 22% higher power conversion efficiencies than reference devices. In order to elucidate the underlying reason for such high improvement, finite-difference time-domain simulations of whole OPV devices under AM1.5G solar illumination were performed. The results revealed up to 25 times higher local exciton generation rate in close proximity to the Au nanostructures and ETLs.