Organic Bulk-Heterojunction Photovoltaics Based on Alkyl Substituted Discotics


  • This work was supported by funds from the Deutsche Forschungsgemeinschaft (Schwerpunktprogramm: Organische Feldeffekttransistoren) and the EU project NAIMO (Integrated Project Number NMP4-CT-2004-500355). M.K. thanks the “Fonds der Chemischen Industrie” for graduate fellowships.


The photovoltaic behavior of three hexa-peri-hexabenzocoronene (HBC) derivatives has been investigated with respect to the influence of the alkyl side chains. Upon increasing the side chain length, the HBC chromophore becomes diluted, thus decreasing the amount of light absorbed. Differential scanning calorimetry and powder X-ray analysis reveal that the HBC with the 2-ethyl-hexyl side chain is in a crystalline state at room temperature, while the other two HBCs containing 2-hexyl-decyl and 2-decyl-tetradecyl substituents in so-called plastic crystalline state. The HBC with the shortest side chain is proven to be the best donor for perylenediimide, showing a highest external quantum efficiency of 12 %. Furthermore, scanning electron microscopy imaging suggested an important role of the morphology of the active film in determining the performance of the device.