Speaker
Description
The interest in CuInS2 (CIS) quantum dots (QDs) has increased significantly in the past few years due to broad range of their potential applications, such as photodynamic therapy or solar cells [1]. This owes to extraordinary optoelectronic properties of this material, such as broad photoluminescence with a large Stokes shift and long charge carrier lifetimes. To elucidate the origin of these unique features, several mechanisms for the radiative recombination in CIS QDs have been proposed theoretically and experimentally.
In this work we aim to understand and confirm the possibility of observing the radiative recombination resulting from an electron in the conduction band and a hole in the so-called confined hole state [2-3], next to the effects of stoichiometry and Zn doping on the passivation of the QDs and the formation process of the CHS [4]. The range of such possible hole trapping states would explain the broad photoluminescence and the large Stokes shift.
We approached these questions through a combination of ultrafast laser and XFEL pump-probe techniques complemented with steady-state synchrotron measurements. The element and oxidation state specificity of X-ray techniques will serve as a direct probe to track recombination and localization dynamics of photogenerated holes, while optical probes will follow the electron dynamics. We focused our X-ray studies on following the oxidation state of Cu via femtosecond-resolved Cu K-edge XANES and comparing the electronic and geometric structures of different samples obtained from static XANES and EXAFS at Cu, Zn and S K-edges. This allowed us to gain insights and correlate the observed charge carries dynamics with the underlying CIS QD structures, the degree of their surface passivation and the different Zn doping levels.
[1] J. Kolny-Olesiak, H. Weller; ACS Appl. Mater. Interfaces 5, 12221 (2013)
[2] W. van der Stam, et al.; ACS Nano 12, 11244 (2018)
[3] A. Fuhr, et al.; ACS Nano 14, 2212 (2020)
[4] B. R. C. Vale, et al.; J. Phys. Chem. C 124, 27858 (2020)
