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

Abstract

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 H-1 and C-13 NMR spectra of RP1 confirmed the formation of ROMP polynorbornene with pendant PCBM group. RP1 possessed high decomposition temperature of 432 degrees C and moderate glass transition temperature of 127 degrees C, but was thermally cross-linked at 80 degrees 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 degrees C. In contrast, the devices based on the P3HT:P1 active layer showed high thermal stability up to 150 degrees C with no decrease in the device performance.