Developing perylene diimide based acceptor polymers for organic photovoltaics

Perylene diimides are known as promising n-type semiconductor building blocks. Here we report the synthesis and characterization of a set of three soluble poly(perylene diimide)s and their preliminary characterization in organic photovoltaic cells. These polymers are made through the polycondensation of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) with a variety of poly(ethylene glycol) (PEG)- or poly(propylene glycol) (PPG)-based diamine comonomers. The flexible spacer offers increased solubility in organic solvents and allows the perylene core to assume a conformation that promotes favorable cofacial π–π interactions. Mixtures of these polymers with the hole-transporting polymer, poly(3-hexylthiophene) (P3HT) result in significant fluorescence quenching. However, the phase separation occurs on a scale too large for a bulk heterojunction solar cell. The PPGylated poly(perylene diimide) shows an unusually low free electron concentration (∼1.0 × 1012 cm−3) and therefore makes an excellent model system for future doping studies. These new polymers may have promise as stable electron-conductive layers with large light-absorptivities in solution-processable applications of organic electronics.