Transferable, conductive TiO2 nanotube membranes for optoelectronics

We report a facile approach for preparing free-standing and crystalline TiO2 nanotube membranes (TNMs) by taking advantage of differential mechanical stress between two anodic layers. The membrane exhibits visible light transmittance (similar to 40%) and UV absorption (similar to 99%) with good flexibility, which is favorable to integrate with substrates in optoelectronics. A sandwich-type device is assembled through stacking the membrane and substrates. The dependence of current-perpendicular-to-membrane vs applied voltage shows a remarkable photoconductive performance for both front and back illumination. The photocurrent value increases 2 or 3 orders magnitude under UV light radiation as compared to that in darkness. The photoresponse is arisen from high internal gain caused by hole trapping along the nanotube walls. This work is crucial for understanding intrinsic optical properties of nanostructured membranes. (C) 2014 Elsevier B.V. All rights reserved.