Photovoltaic Effect in Phthalocyanine-Based Organic Solar Cells: 1. Thermal Ionization of Molecular Excitons

Based on the previously obtained data [1, 2], according to which the photoelectric quantum yield (Y) in crystals of the β-form of metal-free phthalocyanine and copper phthalocyanine is the same for electrons and holes and has an Arrhenius temperature dependence with an activation energy EY equal to the difference between the band gap and the molecular exciton (ME) energy, a three-dimensional stochastic model of thermal ionization of MEs is proposed, which is considered as a sequence of reversible transitions from the ME to the lowest charge-transfer (CT) state and then to a CT state with an increasing charge-transfer distance. A relationship has been found between EY and the radial density of CT states at which the probability of charge separation is greater than that of the decay of these states.