Polymer solar cells based on quinoxaline and dialkylthienyl substituted benzodithiophene with enhanced open circuit voltage

Abstract

A poly[benzodithiophene-alt-di-2-thienyl-quinoxaline] series (PBDTDPQ-EH, PBDTDPQ-OD, and PBDTDPQ-HDT) was synthesized via Stille coupling. Deep highest occupied molecular orbital (HOMO) levels were achieved by the introduction of 2-decyl-4-hexyl-thiophen-yl (HDT) side chains. The introduction of the various side chains increased the molecular weight of the polymers, and the polymers dissolved well in common organic solvents at room temperature. The HOMO energy level (−5.20 to −5.49 eV) decreased because of the 2D conjugated structure. X-ray diffraction analysis showed that PBDTDPQ-OD had a slightly edge-on structure. In the case of PBDTDPQ-HDT, however, the structure was amorphous due to the thiophene side chain, and the extent of π stacking increased. After fabricating bulk-heterojunction-type polymer solar cells, the OPV characteristics were evaluated. The values of open-circuit voltage (Voc), short-circuit current (Jsc), fill factor, and power conversion efficiency (PCE) were 0.88 V, 7.9 mA cm−2, 45.4%, and 3.2%, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1028–1036