Physical, optical, electronic properties and mobility measurements of a new donor–acceptor–donor oligomer

A new organic compound (tertmethoxy di-triphenylamine di-thiophene-benzothiadiazole; DTBT-DTPA-TMeO) recently synthesized displays two strong absorption peaks in the visible range of the solar spectrum. Thermal behavior of this new donor–acceptor–donor (D–A–D) oligomer is investigated by differential scanning calorimetry and thermogravimetric analysis. The decomposition temperature is found to be at about 400 °C and a smectic mesophase transition at about 115 °C (crystal liquid–crystal transition). Solution and solution processed films onto ITO and ITO/MoO3 are characterized by UV–Vis, AFM and XPS-UPS measurements. An optical band gap of 1.85 eV is reported from the UV–Vis data and agrees well with the theoretical value of 1.99 eV. AFM analysis of spin coated films shows smooth uniform coverage free of pin holes. Work functions and HOMO energy values are determined from UPS measurements and allow the construction of an energy band diagram. The hole mobility for a un-annealed single diode device is measured at about 10−5 cm2/Vs.