Charge conduction process and photoelectrical properties of bulk heterojunction device based on sulphonated nickel phthalocyanine and rose Bengal

The dependence of photovoltaic performance of the bulk heterojunction photovoltaic device based on the blend of sulphonated nickel phthalocyanine (NiPcS) and rose Bengal (RB) on their composition, thermal annealing and oxygen exposure has been investigated. It is found that both electron and hole mobility in RB phase and NiPcS phase, respectively has been increased on thermal annealing. The power conversion efficiency of the device increases upon thermal annealing, attributed the balance charge transport. The power conversion efficiency of the device experiences a drastic increase upon oxygen exposure, which attributed to the photo-induced doping, increase in exciton diffusion length in NiPcS phase and increased volume of exciton dissociation interfacial sites. From the impedance spectroscopy, we conclude that the change in bulk resistance and dielectric constant of the active material due to the illumination has a direct relevance to the photocurrent generated by the device.