Enhancement in the Inherent Photostability of Small Molecule-Based Bhj Device by Molecular Architecturing

Three small molecules of D-A-D architecture were synthesized with benzothiadiazole as basic acceptor unit. The first small molecule, TBT (4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole) was designed with benzothiadiazole- acceptor, and thiophene moiety as the donor unit. The effect of fluorine substitution and incorporation of fused donor moiety on the optical electrochemical, photovoltaic and photostability of the molecules were evaluated. The photostability study on the molecules and blend with PCBM shows promising results. Structural modifications of the p-type molecules exhibit an improved photostability of neat films by significantly. The photostability of the active layer comprised of small molecule- PCBM blend has increased by >13.8 times on incorporation of fused thienothiophene and by a factor of >5.2 on fluorination of acceptor. The results suggest that the structural modification p-type materials not only improve the optical, electrochemical and photovoltaic properties, but also the photostability of BHJ active layer