Highly efficient ultraviolet photodetectors based on TiO2 nanocrystal-polymer composites via wet processing

Solution-processed inorganic/organic hybrid films based on anatase TiO2 nanocrystals and poly (9,9-dihexylfluorene) (PFH) are fabricated via a simple spin-coating method and characterized by atomic force microscopy, UV-vis absorption and photoluminescence spectra. The photodetector devices are made from hybrid TiO2/PFH bulk heterojunction films sandwiched between poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) pre-coated ITO and Al electrodes. The device characteristics, including current-voltage (I-V) curves under UV illumination, spectral response, response time and bias dependence, are studied. The photovoltaic effect is observed and the photocurrent shows an increase with increasing TiO2 content from 2.5 to 11 wt%. The high UV photo-to-dark current ratio of 103, fast response time less than 200 ms and a responsivity of 54.6 mA W-1 are obtained for the hybrid photodetector. The fast photoresponse is attributed to the enhanced interfacial dissociation of excitons. The overlap of the spectral response with the UV-A range (320-400 nm) and the low-cost wet fabrication method show their potential for environmental and biological uses.