Taking Advantage of the Giant sp-d Exchange Interactions in Mn-doped CdS Quantum Dots for Applications in 2D-Perovskite Photovoltaics

The purpose of this research is to examine the Mn2+ d-d emission in Mn-doped CdS quantum dots of varying sizes, which were produced via a wet-chemical method using 1-thioglycerol as a capping agent. By adjusting the reaction temperature, we were able to control the size of the quantum dots. Scanning tunneling microscopy and spectroscopy (STM/S) measurements revealed the presence of Mn-induced in-gap states, as well as a significant shift in the valence band caused by a strong exchange interaction. As the size of the Mn:CdS quantum dots increased, the photoluminescence (PL) spectra shifted from two broad peaks to a single peak. When we combined the STS and PL spectra data, we observed that the in-gap states in STS corresponded to the Mn2+ d-d transition seen in the PL spectra. On the other hand, the STS band edges corresponded to the higher energy transitions observed in the PL spectra. Density functional calculations supported our experimental findings by indicating a larger exchange coefficient for Mn-doped CdS as the quantum dot size increased. Additionally, we investigated the optoelectronic properties of Mn-doped CdS and CdS in a heterostructure with the 2D MA2CoCl4 layer. Our initial results show a significant improvement in the optoelectronic properties of CdS when it is used in a heterostructure with 2D MA2CoCl4 perovskite.