Wide band-gap organic molecules containing benzodithiophene and difluoroquinoxaline derivatives for solar cell applications

Two new semiconducting organic small molecules, namely BDTQ-BDT(EH) and BDTQ-BDT(OC), were prepared by attaching electron accepting 2,3-didodecyl-6,7-difluoro-5,8-di(thiophen-2-yl)quinoxaline (DTQ) unit on 2,6-position of electron donating 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene (BDT(EH)) and 4,8-bis(octyloxy)benzo[1,2-b:4,5-b']dithiophene (BDT(OC)) units. Molecule BDTQ-BDT(EH) showed higher thermal stability (5% weight loss temperature, T-d ?349 C-?), slightly lower band-gap (E-g ?2.10?eV) and deeper highest occupied molecular orbital energy level (HOMO ??5.36?eV) level compared to those (T-d ?336 C-?, E-g ?2.11?eV, and HOMO ??5.30?eV, respectively.) of the molecule BDTQ-BDT(OC). The organic solar cells (OSCs) made with the synthesized molecules as an electron donor and [6,6]-phenyl C-71 butyric acid methyl ester (PC70BM) as an electron acceptor gave a maximum power conversion efficiency (PCE) of 1.20% and 0.83%, respectively, for BDTQ-BDT(EH) and BDTQ-BDT(OC). This study confirmed that the substituents attached on the 4,8-position of BDT unit greatly alter the properties of the resulting molecules.