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 (VOC) 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-C61 butyric acid methyl ester) blend showed a power conversion efficiency (PCE) of 1.9%, with a VOC of 0.70 V, and a short circuit current (ISC) of 6.97 mA/cm2, suggesting that PDTPTPD is a promising photovoltaic polymer.