Photogeneration and photovoltaic effect in blends of derivatives of hexabenzocoronene and perylene

Photogeneration quantum yield in layers of discotic liquid crystals (DLC, hole transport material), perylene derivative (electron transport material) and of their mixtures were determined by using surface potential decay technique. While in pure DLC only very weak photogeneration in the visible range was detected, and in pure perylene derivative only negative mobile charge carriers were photogenerated, in the mixtures a synergetic effect of photogeneration of both positive and negative mobile charge carriers was observed. This is because the excitons photogenerated at perylene derivative dissociate into electron-hole pairs, and then electrons are transported via perylene derivative while the holes are transferred onto the DLC molecules. The obtained results were correlated with performance of the photovoltaic devices with active layer made of the mixtures of the DLC and perylene derivative and of their blends with photoconducting polymer. It was found, that the power conversion efficiency of the device is dependent on the film morphology.