Synthesis, characterization, and photovoltaic property of a low band gap polymer alternating dithienopyrrole and thienopyrroledione units

The lower the highest occupied molecular orbital (HOMO) energy level of the conjugated polymer is, the higher the open-circuit voltage (V-OC) of the obtained polymer solar cell (PSC) is. To achieve this goal, a new conjugated polymer (PDTPTPD) alternating dithienopyrrole (DTP) and thienopyrroledione (TPD) units was designed and synthesized by Stille coupling reaction. Through UV-vis absorption and cyclic voltammetry (CV) measurements, it was found that the resulting copolymer exhibited both a low optical band gap of 1.62 eV and a low HOMO energy level of -5.09 eV owing to the electronegativity of TPD moiety. Preliminary photovoltaic study disclosed that the PSC based on PDTPTPD:PCBM ([6,6]-phenyl-C-61 butyric acid methyl ester) blend showed a power conversion efficiency (PCE) of 1.9%, with a V-OC of 0.70 V. and a short circuit current (I-SC) of 6.97 mA/cm(2), suggesting that PDTPTPD is a promising photovoltaic polymer. (C) 2011 Elsevier Ltd. All rights reserved.