Planar Donor-acceptor Copolymers for Bulk Heterojunction Solar Cells

Two planar conjugated copolymers poly2,8-{5,11-diisooctylindolo[3,2-b]carbazole[-4,7-di[2,5-thiophene]-5,6-dioctyloxy-2,1,3-benzothiadiazole(QP-2) and poly2,8-{5,11-dioctylindolo[3,2-b]carbazole[-4,7-di[2,5-thiopene]-5,6-dioctyloxy-2,1,3-benzothiadiazole(QP-3) with main chain donor-acceptor alternating structures were synthesized and their photophysical and photovoltaic properties were investigated. Photovoltaic cells based on polymer QP-3 gave a power conversion efficiency (PCE) of 2. 59%, an open circuit voltage (V-oc) of 0. 72 V, a short circuit current density (J(sc)) of 9. 24 mA/cm(2), and a fill factor(FF) of 0. 38. The results show that the polymer without branched alkyl side group performs better and they have better crystallinity in solid film.