Photoconductivity of n-type semiconductor nanoparticle-doped poly(N-vinylcarbazole) films

TiO2, CdS and ZnS nanoparticles that disperse stably in organic solvents are synthesized. Poly(N-vinylcarbazole) films doped with the n-type semiconductor nanoparticles are prepared with a cast method. The films exhibit a transient photocurrent when irradiated by a light pulse and act such as a diode when AC voltage is applied under continuous illumination. The transient photocurrent response and diode-like properties are significantly different depending on the kind of the nanoparticles and their amounts. The films doped with TiO2 and CdS nanoparticles increase the transient photocurrent at lower doped amounts, which is remarkable for TiO2-doped films. Time of flight analysis of the transient photocurrent shows that mobility of hole in PVK increases with increase in the amount of CdS and TiO2. From the studies on the diode-like properties, the current increase at lower dopant concentration is concluded to be due to increase in the amount of holes by an electron transfer from PVK to the photo-excited nanoparticles. At higher doping with CdS nanoparticles, main charge carrier of the films is found to change from holes to electrons.