Organics filled one-dimensional TiO2 nanowires array ultraviolet detector with enhanced photo-conductivity and dark-resistivity

Abstract

A heterojunction photo-conductive ultraviolet (UV) detector was developed based on TiO₂ nanowires array (NWA) surrounded by N,N′-bis-(1-naphthalenyl)-N,N′-bis-phenyl-(1,1′-biphenyl)-4,4′-diamine (NPB). The novel and effective two-step method of static infusion and dynamic solution-cleaning was employed to fill NPB into TiO₂ NWA gaps and simultaneously remove the unwelcomed top NPB layer. The device fabricated via the two-step method exhibited optimal performance compared to TiO₂/NPB device with top NPB layer and TiO₂ NWA device. In dark conditions, the TiO₂/NPB heterojunction device without top NPB was found to possess the capacity of depleting majority carriers, thereby providing improved dark-resistivity to limit the dark current (I_d). Under UV illumination, the depleting effect could be eliminated by the dissociation and accumulation of photo-generated carriers between pn heterojunction, leading to increased carrier density and photo-conductivity. It cleared up the high barrier due to the removal of top NPB layer, which was beneficial for hot electron transport than the device with top NPB layer under illumination, thereby achieving an enhanced light current (I_l) to I_d ratio of 1.67 × 10⁴. A simple technology is provided to prepare organic–inorganic hybrid one-dimensional array heterostructure, which plays a remarkable role in the working of the UV detector, enhancing photo-conductivity and dark-resistivity of the device.