Photogeneration process in pristine sexithiophene based photovoltaic cells

The photogeneration process in organic photovoltaic cells may occur via multiple mechanisms depending on their structure and/or architecture. Nevertheless, in the case of pristine material sandwiched between two dissimilar work function electrodes, photogenerated free carriers in the bulk are most likely to result, according to Onsager’s theory, from dissociation of excitons at a given electric field E. It has been reported that one of the most limiting factors for efficiency in photovoltaic organic cells is the recombination of e–h pair which is of bimolecular type. In this work we show that bulk photogeneration is rather dominated by the initial separation of geminate e–h pair which accounts for poor I–V characteristics of organic (non-heterojunction) photovoltaic cells.