Significantly enhanced photoresponse in carbon nanotube film/TiO2nanotube array heterojunctions by pre-electroforming

Traditional TiO2 based photodetectors (PDs) suffer from high dark resistance, which increases loss of photoexcited charge carriers. Here, we report a new and simple way to improve the performance of PDs based on double-walled carbon nanotube (DWCNT)/TiO2 nanotube heterojunctions. Highly ordered TiO2 nanotube arrays were fabricated using a two-step anodic oxidation method, and coated with a DWCNT film, which functioned as a semitransparent electrode and a photoactive layer. Via pre-electroforming, the device was switched from a high resistance state (HRS) to a low resistance state (LRS). At an applied bias of 1 V, the dark resistance was reduced from 926 to 0.67 kΩ, as a result of the formation of oxygen vacancy related conducting filaments. The photoresponse (ΔI = Ip - Id, where Ip and Id represents photocurrent and dark current, respectively) of the PD in LRS reached 816.76 μA W(-1) under 532 nm laser illumination and 802.89 μA W(-1) under 1064 nm laser irradiation, which is 965 and 3980 times higher, respectively, than those obtained from the HRS device under the same conditions. This strategy for enhancing the photoresponse of TiO2 based PDs may have applications in further improving the power conversion efficiency of dye-sensitized solar cells.