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 °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/cm2 irradiation.