Polynorbornenes with pendant PCBM as an acceptor for OPVs: Ring-opening metathesis versus vinyl-addition polymerization

Polynorbornenes with pendant [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) moieties were produced by ring-opening metathesis polymerization (ROMP) of norbornene monomer functionalized with PCBM using a Grubbs second-generation catalyst. The resulting ROMP polymers (RP1 and RP2) are soluble in o-dichlorobenzene (ODCB) and CS2 at ambient temperature. The 1H and 13C NMR spectra of RP1 confirmed the formation of ROMP polynorbornene with pendant PCBM group. RP1 possessed high decomposition temperature of 432 °C and moderate glass transition temperature of 127 °C, but was thermally cross-linked at 80 °C. The absorption property of RP1 is very similar to those of monomer and vinyl-type polynorbornene bearing PCBM moiety (P1). While the bulk-heterojunction organic photovoltaic devices fabricated with the active layer comprising poly(3-hexylthiophene) (P3HT) donor and RP1 acceptor at ambient temperature exhibited a power conversion efficiency of 0.66%, the efficiency decreased to 0.28% after pre-annealing of the active layer at 110 °C. In contrast, the devices based on the P3HT:P1 active layer showed high thermal stability up to 150 °C with no decrease in the device performance.