In the rapidly advancing field of organic electronics, soluble small molecules have recently shown a considerable increase of interest in the specific field of organic photovoltaic applications due to the reported increase in power conversion efficiency. In this work, we will present recent chemical and physical advances relative to the use of the triazatruxene (TAT) moiety as a versatile platform for the synthesis of efficient soluble electron-donor small molecules to be used in bulk heterojunction organic solar cells. Recently, we demonstrated the interest of TAT as planar moiety used in dumbbell-shaped molecules. Using a thiophene-diketopyrrolopyrole as chromophore unit in between two end-capping TAT, we obtained a PCE of 5.3% with a high fill-factor (FF) of almost 60%.[1] This relatively high FF value has been attributed mainly to the planar TAT moiety which allows efficient π-stacking interactions and consequently an efficient charge carrier mobility. Since this preliminary work, we developed a new series of molecules based on a chromophore unit in between two end-capping TAT. For these new molecules, we found some interesting correlations between the chemical structure of the conjugated core, the nature of the solubilizing side chains and the optoelectronic, structural and photovoltaic properties of the soluble small molecules. In particular we will show how a fine-tuning of the chemical structure could lead to an increase in photovoltaic performances.
[1] T. Bura, N. Leclerc, R. Bechara, P. Lévêque, T. Heiser and R. Ziessel, Advanced Energy Materials, 2013, 3, 1118-1124.