Spatially resolved photoconductivity of thin films formed by colloidal octapod-shaped CdSe/CdS nanocrystals

We studied the optical absorption and photoconductive properties of thin films consisting of core-shell octapod-shaped nanocrystals, which consisted of CdS pods that branch out from a CdSe core. The current-voltage characteristics were measured at room and cryogenic temperatures and agreed well with a phenomenological exponential fitting model, from which we could extract the sheet resistance and the average voltage barrier for the charge tunneling between the octapods. The temperature dependence of the photocurrent showed temperature activated behavior above 220 K and a non-Arrhenius exponential (T/T-0)(n) dispersion below 220 K. Furthermore, we mapped the photocurrent generation within the octapod film via scanning photocurrent microscopy, which revealed photocurrent enhancement near micron-size voids and spatial shifts of the photocurrent maxima with bias voltage.