Solution processable D-A-D molecules based on triphenylamine for efficient organic solar cells

Two new D-A-D molecules containing triphenylamine (donor), benzothiadiazole (acceptor) and thiophene (bridge) units - single-bond (P1) and double-bond (P2) linked - have been synthesized for application in solution-processed organic solar cells (OSCs). The thermal, absorption, emission, and electrochemical properties of the molecules were examined; the effect of the link pattern was studied. P1 is crystalline, while P2 is amorphous. Both compounds possess excellent thermal stability with decomposition temperatures over 370 degrees C. Compared to P1, P2 exhibits red-shifted and broader absorption and red-shifted emission. Their LUMO levels (ca. -3.0 to -3.1 eV) are similar, while the HOMOs (-4.9 to -5.2 eV) are a little more sensitive to the link pattern. OSCs were fabricated based on the blend of P1 or P2 and soluble fullerene derivatives PC61BM or PC71BM. The OSCs based on P1:PC61BM exhibit higher open circuit Voltage and higher power conversion efficiency (PCE) than that for P2:PC61BM, which is attributed to the lower HOMO level of P1. The OSCs based on P1:PC71BM (1:3, w/w) yielded a PCE of 1.23% under simulated AM 1.5, 100 mW/cm(2) irradiation. (C) 2009 Elsevier B.V. All rights reserved.