Solution-Processable Organic Molecule Photovoltaic Materials with Bithienyl-benzodithiophene Central Unit and Indenedione End Groups

Two solution-processable acceptor donor acceptor (A-D-A) structured organic molecules with bithienyl-substituted benzodithiophene (BDTT) as central and donor unit, indenedione (ID) as acceptor unit and end groups, and thiophene (T) or bithiophene (bT) as pi-bridges. D1 and D2, are designed and synthesized for the application as donor materials in organic solar cells (OSCs). Two corresponding molecules with alkoxy side chains on BDT, DO1 and DO2 are also synthesized for comparison. The four compounds possess broad absorption covering the wavelength range 450-740 nm and relatively lower HOMO energy levels from -5.16 to about -5.19 eV. D2 and DO2 with bithiophene pi-bridges demonstrate stronger absorbance and higher hole mobilities than the compounds with thiophene pi-bridges. The power conversion efficiency (PCE) values of the OSCs based on the organic compounds/PC70BM (1.5:1, w/w) are 6.75% for D2, 5.67% for D1, 5.11% for DO2, and 4.15% for DO1. The results indicate that the molecules with thienyl conjugated side chains and bithiophene pi-bridges show better photovoltaic performance. The PCE of the D2 based OSC are among the highest values in the OSCs based on the solution-processed organic small molecules.