Effect of the Introduction of Ethylenedioxythiophene and Styrilnitroisooxazol Groups on the Properties and Photovoltaic Performances of Tryphenylamine Based Π −conjugated Push-Pull Molecules

Properties of pi-conjugated push-pull molecules based on triphenylamine have been modified through the introduction of ethylenedioxythiophene and a styrilnitroisooxazol group. It is shown that the obtained new molecule called GC8 exhibits light absorption in the visible, between 400 nm and 700 nm and a high hole mobility of 210-5 cm2V- 1s- 1, which places this organic donor among those with good mobility in this family of compounds. It behaves as electron donor in organic photovoltaic cells, with a HOMO of 5.35 eV, a LUMO of 2.94 eV which gives a band gap of 2.41 eV, these values being obtained from theoretical estimation using TD-DFT theory. The measured experimental optical band gap is 1.9 eV, this difference in value between theory and experiment is reasonable for small molecules. GC8 has been introduced as electron donor in planar heterojunctions organic photovoltaic cells (PHJ-OPVs), fullerenes (C60 or C70) being used as electron acceptor. It is shown that the optimum GC8 layer thickness is 20 nm, while a 5 min annealing at 100 degrees C improves the power conversion efficiency (PCE) by 10%. The high light absorption of C70 allows improving cells performances compared to that using C60, the champion cell having a 6.15% efficiency. The PCE improvement after the annealing is due to an increase of the hole mobility and optical absorption.