Impact of the molecular structure of an indandione fragment containing azobenzene derivatives on the morphology and electrical properties of thin films

The solution casting method is low-cost processing method. Moreover, it is possible to prepare amorphous thin films by using this method, and thus, both optical quality and electrical properties could be improved in compare to polycrystalline films made by thermal evaporation in vacuum. Therefore, low-molecular-weight compounds that form amorphous structure from solution could be promising in organic electronics. In this work film morphology, molecule energy levels, and charge carrier mobility in thin films of indandione fragment containing azobenzene derivatives were studied. Deep charge carrier trapping states that drastically influenced charge carrier mobility were observed for polycrystalline films with the model compound 2-(4-((4-(dimethylamino)phenyl)diazenyl)benzylidene)-1H-indene-1,3(2H)-dione. This issue was overcome by attaching bulky groups to the model compound. An amorphous thin film without deep trapping states was obtained. Electron and hole mobilities of these materials at electric field 160 to 600 kV/cm were between 10^-5 and 10^-6 cm²V^-1s^-1 and between 10^-6 to 10^-7 cm²V^-1s^-1, respectively. Charge carrier mobility, molecular ionization energy, and electron affinity energy were influenced by bulky groups.