New 4,7-dithienebenzothiadiazole derivatives with cyano-vinylene bonds: Synthesis, photophysics and photovoltaics

Two conjugated compounds P and T which contained 4,7-dithienbenzothiadiazole as central unit and terminal phenyl or thiophene rings, respectively, connected via a cyano vinylene bond, were synthesized. The stable intramolecular charge-transfer status makes possible the compounds to increase the optical absorption band. These compounds exhibited excellent film-forming properties which allowed the preparation of homogenous thin films by the spin-coating technique. The compounds were stable up to about 300 °C and showed glass transition temperatures of 64 and 50 °C. The absorption spectra were broad and extended from about 300 to 700 nm. They emitted yellow-orange light in solution with photoluminescence (PL) maximum at 574, 578 nm and reddish light in solid state with PL maximum at 663, 702 nm. Organic solar cells based on T (or P) as donor and C60 derivative as acceptor exhibit power conversion efficiencies (PCEs) of 0.11% (or 0.09%) under one sun of AM1.5 illumination.