PNNT has been prepared as a polymeric electron acceptor for organic solar cells. The polymer has an A-A'-A acceptor motif linked alternatively with thiophene and vinyl moieties. The A'-unit is a naphthalene diimide, while the A groups are thiazoles. PNNT films were found to have an estimated electron affinity of ≈4.3 eV and an electron mobility of the order of 10-4 cm2 V-1 s-1. Its relatively low solubility in common chlorinated solvents at ambient temperature allowed the manufacture of sequentially deposited (SD) devices, which were found to have significantly higher efficiency than that of bulk heterojunction (BHJ) solar cells containing the same materials. Grazing-incidence wide-angle X-ray scattering measurements indicated that the SD films retained the ordering of the individual polymers to a greater extent compared to the BHJ films. The best SD devices were found to have a power conversion efficiency of up to 4.5%, with stable performance under thermal stress.
Keywords: electron mobility; organic solar cells; polymeric electron acceptor; sequentially deposited; solution-processed.