Temperature-driven charge transport in annealed CdSe/CdS nanoplatelets film

Abstract

This work presents a comprehensive investigation into the temperature-dependent thermally stimulated conductivity and photoconductivity of vacuum-annealed thin films based on core–shell CdSe/CdS nanoplatelets passivated with oleic acid ligands. Controlled thermal annealing under vacuum conditions leads to a substantial increase in both dark and photoinduced conductivity, which is primarily attributed to partial desorption of the ligands. This process enhances interparticle electronic coupling while preserving the key optical properties of the nanostructures. Consequently, the fabricated single-layer photodetector demonstrates high responsivity, highlighting the potential of ligand-engineered nanoplatelet films for optoelectronic applications. Detailed analysis of the temperature-dependent conductivity enabled the characterization of hole-trapping states within the bandgap of the metamaterial. The extracted effective attempt-to-escape frequency is remarkably low, νeff ≈ 1.5 × 104 s−1, indicating strong carrier localization and large capturing cross section. The density of states can be characterized by Gaussian function with a pronounced maximum at an energy of approximately 0.345 eV above the transport level and a dispersion below 34 meV. These parameters were consistently derived from both thermally stimulated conductivity and photoconductivity measurements through rigorous statistical modeling of thermally released charge carriers. The excellent agreement between the two independent experimental techniques further validates the reliability of the obtained trap-state characteristics.