Synthesis and Electro-Optical Properties of Fluorene-Based Copolymer for Organic Photovoltaic Device Application

The following soluble pi-conjugated polymer was synthesized by palladium-catalyzed Suzuki polymerization: poly[(9,9-dioctylfluorene)-alt-(3-hexylthiophen-5-yl)(4'-hexylthiazol-5'-yl)] poly(FO-HThHTha) derived from poly(9,9-dioctylfluorene) (PFO) and poly[(3-hexylthiophen-5-yl)-2,2'-(4'-hexylthiazol-5'-yl)] poly (HThHTa). The polymer, poly(FO-HThHTa) was soluble in common organic solvents and easily spin coated onto indium-tin oxide (ITO) coated glass substrates. Bulk heterojunction photovoltaic cells with an ITO/PEDOT/poly(FO-HThHTa): PC70BM/TiOx/Al configuration were fabricated and the photovoltaic cell using poly(FO-HThHTa): PC70BM (1: 4) showed the best photovoltaic performance compared with those using poly(FO-HThHTa): PC70BM (1: 2 and 1: 6). The optimal bulk heterojunction photovoltaic cell exhibits a power conversion efficiency (PCE) of 0.39% (V-oc = 0.44 V, J(sc) = 2.57, FF = 0.34) with poly(FO-HThHTa): PC70BM (1: 4) measured by using an AM 1.5G irradiation (100mW/cm(2)) on an Oriel Xenon solar simulator (Oriel 300 W).