Solution-ProcessableOrganic Molecule PhotovoltaicMaterials with Bithienyl-benzodithiophene Central Unit and IndenedioneEnd Groups.

Two solution-processableacceptor–donor–acceptor(A-D-A) structured organic molecules with bithienyl-substituted benzodithiophene(BDTT) as central and donor unit, indenedione (ID) as acceptor unitand end groups, and thiophene (T) or bithiophene (bT) as π-bridges,D1 and D2, are designed and synthesized for the application as donormaterials in organic solar cells (OSCs). Two corresponding moleculeswith alkoxy side chains on BDT, DO1, and DO2 are also synthesizedfor comparison. The four compounds possess broad absorption coveringthe wavelength range 450–740 nm and relatively lower HOMO energylevels from −5.16 to about −5.19 eV. D2 and DO2 withbithiophene π-bridges demonstrate stronger absorbance and higherhole mobilities than the compounds with thiophene π-bridges.The power conversion efficiency (PCE) values of the OSCs based onthe organic compounds/PC70BM (1.5:1, w/w) are 6.75% forD2, 5.67% for D1, 5.11% for DO2, and 4.15% for DO1. The results indicatethat the molecules with thienyl conjugated side chains and bithiopheneπ-bridges show better photovoltaic performance. The PCE of theD2-based OSC are among the highest values in the OSCs based on thesolution-processed organic small molecules. [ABSTRACT FROM AUTHOR]