In order to develop large-area,low-c ost and high-quality photodiodes,in this pater,well-aligned ZnO nanowire array s (ZNWAs) were grown on indium tin oxide (ITO)-coated glass substrate by a facil e chemical bath deposition method.A photodiode with a structure of ITO/ZNWAs/P3HT/Ag was fabric ated using ZNWAs and regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT).The current-voltage (I-V) characteristics of the photodiode in dark and under illumination with a solar simulator are investigated in deta i l.The results demonstrate that the device shows good diode characteristics in dark and under illumination.It exhi bits a rectification ratio (RR) of 3211at ±2V and ideality factor of 1.8in dark.Under 20mW/ cm^2power illumina tion,an RR of 39.1is achieved at ±2V,a large number of photo-generated carriers are produced in the de vice,and their transportation process is illuminated in terms of energy band diagram.