Synthesis of Novel Push-Pull Chromophores based on N-Ethylcarbazole for Vacuum Deposition Processed Organic Photovoltaics

Two novel p-type materials, Cz(Et)ThOM and Cz(Et)OM- respectively with and without a thiophene pi-spacing unit-have been synthesized for vacuum-deposited organic photovoltaics (OPVs). The power conversion efficiencies of planar heterojunction OPVs of the former are clearly higher than that of the latter. Further improvement of the device with Cz(Et)ThOM was obtained by employing bulk heterojunction structure and post-annealing. The structural analysis of thin films by synchrotron X-ray diffraction and atomic force microscopy shows that this improvement is due to Cz(Et)ThOM becoming highly ordered during annealing.