Photosensitive organic field effect transistors: the influence of ZnPc morphology and bilayer dielectrics for achieving a low operating voltage and low bias stress effect

Abstract

Photosensitive-organic field effect transistors (PS-OFETs) based on a morphology controlled zinc phthalocyanine (ZnPc) layer, with an inorganic–organic bilayer gate dielectric system, fabricated on a glass substrate showed remarkable efficiency as light sensors at various incident optical powers. The indium tin oxide (ITO) and Si/SiO₂ free low-cost OFET devices show low bias stress and a reduced operating voltage with aluminum oxide and poly(methyl methacrylate) (Al₂O₃/PMMA) as bilayer gate dielectrics and copper (Cu) as a top contact. They exhibit excellent p-channel behavior with a remarkable photo-responsivity of 2679.40 A W⁻¹ and a photo-ON/OFF current ratio of 933.56 with a very low operating voltage (0 to −8 V), which have not been observed previously. The bias stress effect of the device was investigated under both light and dark conditions in a vacuum. It was observed that the effect of the stress is extremely small in the presence of light (a decay of I_DS of ∼ 20% after 30 min) compared to the dark, with a characteristic carrier relaxation time τ′ ∼ 10⁴ s. This device with high electrical stability under ambient conditions and a low threshold voltage under constant electrical bias stress is expected to have potential applications in optoelectronic devices and energy efficient sensors.