Amorphous molecular material containing bisthiophenyl-benzothiadiazole and triphenylamine with bipolar and low-bandgap characteristics for solar cells

A D-π-A-π-D compound 4,7-bis{5′-[4″,4″-N, N-diphenylamino-styryl]thiophen-2′-yl}benzo[1,2,5-thiadiazole] (TPA-BTD-TPA) with triphenylamine (TPA) as electron-donor and benzothiadiazole (BTD) as electron-acceptor and linked via vinyl unit was synthesized and characterized. A stable intramolecular charge-transfer state enabled the molecule to expand the optical absorption band and prevented the occurrence of electron back-donation. Excellent film-forming property made it easy prepare homogeneous film using a spin-coating technique. Suitable energy levels were beneficial for the improvement of photovoltaic device performance. Photovoltaic cell based on TPA-BTD-TPA/[6,6]-phenyl C61-butyric acid methyl ester as a active layer was fabricated, and the optical conversion efficiency was 0.26% under the illumination of AM 1.5 (85 mW/cm2).