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.