Time-dependent photocurrent of a CdTe nanoparticle film under the above-gap illumination

Time-dependent photocurrent of a solid film of 1-thioglycerol-capped CdTe nanoparticles under the illumination of the 325-nm wavelength light is characterized to investigate the transport mechanism of photo-generated charge carriers in this nanoparticle film. Under the illumination of the above-gap light, photocurrent rises rapidly, and subsequently it decays or rises slowly, depending on the magnitude of bias voltage. A careful investigation into the variation in the magnitude of the current measured as a function of time while the light was switched on and off periodically reveals that rapidly and slowly respondent photocurrents overlap in the time-dependent photocurrent. Charge carriers contributing to the rapidly and slowly respondent photocurrents are electrons and holes separated from a fraction of excitons excited by the above-gap light. The transport behaviors of these charge carriers may explain the monotonously decay and slow rising of the photocurrent after its rapidly rising under the illumination for the solid film at unbiased and biased voltage, respectively.