Layer-by-layer fabrication of organic photovoltaic devices: material selection and processing conditions

Abstract

Layer-by-layer (LbL) processing, otherwise known as sequential deposition, is emerging as the most promising strategy for fabrication of active layers in organic photovoltaic (OPV) devices on both laboratory and industrial scales. In comparison to the bulk heterojunction (BHJ) configuration, LbL facilitates separate and sequential deposition of each layer, enabling greater control and optimization of interfaces and final donor/acceptor morphology. Furthermore, this process encourages formation of an efficient vertical phase separation, where the acceptor and donor aggregations are largest at their respective electrodes, increasing exciton dissociation and transport while reducing unwanted charge recombination. Compared to BHJ OPVs, LbL OPVs are more robust, with less dependence on processing conditions, resulting in increased photo, thermal, and mechanical stability and greater power conversion efficiency retention when applied to large area modules. These advantages have resulted in significant interest in the LbL process and its potential to displace BHJ as the dominant process for large-scale OPV manufacturing. This review summarizes recent developments in OPV fabrication through LbL, with particular emphasis on material selection and thin film processing conditions.