Self-assembled monolayers for interface engineering in polymer solar cells

Polymer solar cell (PSC) has been developed vastly in the past decade due to the advantages of low cost, lightweight, mechanical flexibility, versatility of chemical design and synthesis, semitransparency, and solution processing. The performance and lifetime of PSCs are highly dependent on the properties of both active materials and their interfaces. The combination of the versatility of organic chemistry and the multitude of well-understood ligand–metal interactions allows self-assembled monolayers (SAMs) of organic molecules to direct control over the electronic and chemical properties at the inorganic–organic interfaces. Thus, SAMs are an attractive pathway to reconcile interfaces with tunable interface properties in PSCs. Hence, this review describes the application of SAMs in PSCs at different interfaces. First, SAMs as alternatives of traditional transporting materials to reduce the barrier at indium tin oxide (ITO)/active layer interface due to the ability of tuning work function of ITO electrode are discussed. Second, the modifications of metal oxide by SAMs to control the electrical contacts at transporting layer/active layer interface are described. Third, tailoring the properties of the donor/acceptor interface by SAMs to improve the performance of PSCs are summarized. Finally, perspectives and challenges are pointed out for developing highly stable and high-performance PSCs by applying SAMs.