Effect of Nitro Groups on Electrochemical and Photovoltaic Behavior of Tris-thiophenes used in Organic Solar Cells

Abstract

4-[3(5)-(4-aminophenyl) [1(2),2(2):2(5),3(2)-terthiophen]-1(5)-yl]benzonitrile (CB4TA), 4-[3(5)-(4-aminophenyl) [1(2),2(2):2(5),3(2)-terthiophen]-1(5)-yl]-2-nitrobenzonitrile (C2B4TA) and 4-[3(5)-(4-aminophenyl) [1(2),2(2):2(5),3(2)-terthiophen]-1(5)-yl]-2,6-dinitrobenzonitrile (C2,5B4TA), the first molecule without nitrogroups and the others with electron withdrawing nitro-groups, were successfully synthesized. This family of compounds has acceptor and donor moieties in the same molecule. The acceptor and donor functions are separated by a "molecular bridge". All molecules were studied to evaluate the effect of nitro groups on the photovoltaic yield in an organic solar cell (OPVC). CB4TA and the related molecules were characterized via NMR-spectroscopy, optical and electrochemical methods and then deposited by high vacuum sublimation over ITO treated with MoO3 and CuI as buffer layers. Subsequently the morphology of deposits was characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). The photovoltaic devices were built under the same conditions, observing differences in the photovoltaic yield. Results show that the nitro groups have important effects over frontier orbitals and photovoltaic yield.