Polymer Solar Cells: Development of π-Conjugated Polymers with Controlled Energetics and Structural Orders

Abstract

This chapter will summarize the development of π-conjugated polymers with donor-acceptor motifs, specifically, based on thiazolothiazole and naphthobischalcogenadiazoles as the acceptor unit. It is found that careful design of the molecular structure, the crystallinity and the backbone orientation of the polymers can be controlled. With the crystalline structure and favorable face-on backbone orientation, the polymers show high power conversion efficiencies, in particular, with thick active layers of around 300 nm. Further, a polymer system with naphthobisoxadiazole, with a deep molecular orbital energy levels, allows us to have a significantly high open-circuit voltages of close to 1 V even with a narrow bandgap of ~1.5 eV, resulting in a markedly small photon energy loss. These findings will provide beneficial guidelines for the development of high-performance π-conjugated polymers for organic solar cells.