Synthesis and characterization of high molecular weight and regioregular poly[3-(4-octylphenyl)thiophene] for bulk heterojunction photovoltaic cells

Various poly[3-(4-octylphenyl)thiophene]s (POPTs) were prepared either by oxidative polymerisation or by chain-growth Grignard metathesis (GRIM). In accordance with previous results, the former polymerisation yielded polydisperse POPT. The method based on the GRIM reaction made possible the preparation of medium and higher molecular weight polymers with lower polydispersities. The POPTs were found to have band-gaps of ca. 1.7 eV. The photovoltaic characteristics of POPTs-blend-[6,6]-phenyl C61 butyric acid methyl ester (PCBM) composites under AM 1.5 conditions in standard ITO/PEDOT-blend-PSS/ POPT-blend-PCBM/LiF/Al solar cells were studied. It was found that POPT prepared via GRIM could deliver greater efficiencies than its equivalent prepared by oxidative polymerisation. It is expected that access to even higher molecular weight POPTs may improve the efficiencies of such devices