Enhancement of the Efficiency and Stability of Organic Photovoltaic Devices via the Addition of a Lithium-Neutralized Graphene Oxide Electron-Transporting Layer

Abstract

Lithium-neutralized graphene oxide (GO-Li) was spin coated between the photoactive layer and the metal oxide electron-transporting layer (ETL) as an additional interlayer in organic photovoltaic devices. The introduction of GO-Li leads to a superior interface between the ETL and the photoactive layer. Combined with the reduced work function (WF) of GO-Li (4.3 eV), which is a perfect match with the fullerene acceptor material LUMO level, PCDTBT:PC₇₁BM-based air-processed devices with a GO-Li layer exhibited a significant enhancement in their power conversion efficiency (PCE) from 5.51 to 6.29% (14.2% increase over that of comparable devices without the graphene-based interfacial layer). Furthermore, the GO-Li device exhibited stability higher than that of the device without the interlayer due to the fact that the GO-Li acts as an internal shield against humidity, protecting the air sensitive polymers and improving the lifetime of the devices