Low band gap vinylene compounds with triphenylamine and benzothiadiazole segments for use in photovoltaic cells

Two new soluble vinylene compounds, TPA-TNP and BTD-TNP, which contained triphenylamine and benzothiadiazole segments, respectively, and terminal p-nitrophenyl units were synthesized and characterized. They showed high thermal stability with decomposition temperature above 450 °C. Their absorption was broad and extended up to about 800 nm with optical band gaps of 1.65–1.67 eV. The long wavelength absorption maximum was located around in between 638 and 650 nm. The presence of the electron-withdrawing nitro groups on the terminal phenyls broadened the absorption of these compounds. The current–voltage characteristics in dark and the IPCE spectra of the devices based on these compounds revealed that these materials behave as p-type organic semiconductors with hole mobility of the order of 10−5 cm2/V s. The photovoltaic properties of these compounds blended with PCBM were investigated and the power conversion efficiency is 1.13% and 1.32% for TPA-TNP and BTD-TNP, respectively. The device with thermally annealed BTD-TNP photoactive film shows power conversion efficiency of about 2.42%.