Synthesis and characterization of dithienothiophene vinylene based co-polymer for bulk heterojunction photovoltaic cells

An electron-donor-acceptor type co-polymer, PDTTBBO, composed of 3,5-dihexyldithieno [3,2-b:2′3′-d] dithiophene as donor and 2,6-dimethyl benzo[1,2-d; 5,4-d′] bisoxazole as an acceptor unit was synthesized by Horner-Wadsworth-Emmons (HWE) olefination reaction via multi-step procedure. The UV-vis absorption and photoluminescence emission peaks of the co-polymer in chlorobenzene were observed in a range from UV to near 700 nm. The lowest unoccupied molecular orbital (LUMO) and highest unoccupied molecular orbital (HOMO) levels of the co-polymer were estimated at -5.71 eV and -3.46 eV, respectively, corresponding to a band-gap of 2.25 eV. Bulk heterojunction photovoltaic cells were fabricated using a blend of PDTTBBO and PCBM with a ratio of 1:1. The short-circuit current density (J_sc), open-circuit voltage (V_oc) and fill factor (FF) of the device were estimated to be 1.306 mA/cm², 0.628 and 0.37, respectively, corresponding to power conversion efficiency (PCE) of 0.31% under AM 1.5 illumination.