Isoregic conjugated polymers composed of thiophene and dialkoxybenzene units were designed to harvest incident light in the mid-visible energy range (band gap of 2.1 eV). Poly(1,4-bis(2-thienyl)-2,5-diheptoxybenzene) (PBTB(OC7H15)2) and poly(1,4-bis(2-thienyl)-2,5-didodecyloxybenzene) (PBTB(OC12H25)2) have shown significant photovoltaic performance as an electron donor when used in tandem with the electron acceptor [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) in bulk hetero-junction photovoltaic devices. Photovoltaic devices incorporating PBTB(OC7H15)2 and PCBM have shown AM 1.5 efficiencies of similar to 0.6% with a short circuit current density of 2.5 mA/ cm2, an open circuit voltage of 0.74 V, and a fill factor of 0.32. Incident Photon-to-Current Efficiency (IPCE) of the device was found to be ca. 16% at 410 nm. In order to examine the relationship between the molecular structure of the polymers and their electronic energy levels, and to correlate this with photovoltaic performance, optoelectronic and electrochemical results are discussed in relation to the I-V characteristics of the devices. Additionally, a computer-aided simulation is used to gain further insight into the effect of polymer structure on the energetic relationships in the bulk heterojunction devices.
Kim, Y. G., E. M. Galand, B. C. Thompson, J. Walker, S. A. Fossey, T. D. McCarley, K. A. Abboud, J. R. Reynolds
J. Macromol. Sci. Part A Pure Appl. Chem.