Enhancement Mechanism of Quantum Yield in Alloyed-Core/Shell Structure of ZnS-CuInS2/ZnS Quantum Dots

CuInS2 (CIS) quantum dots (QDs) would be attractive alternatives to the widely-investigated QDs containing toxic elements when the quantum yield (QY) of CIS QDs becomes comparable to that of typical QDs. Hence, optical features of CIS are investigated in the alloyed-core/shell structures to figure out the enhancement mechanism of QY. The band gap transition becomes stronger in the alloyed core of ZnS-CuInS2 (ZCIS) due to the evolution of the electronic structures in the solid-solution. The surface-related emission is suppressed in the core/shell structures of ZCIS/ZnS, which also contributes to the improvement of QY. The broad spectral bands suggest the electron-phonon coupling in the self-trapped exciton states of CIS, which is reduced but still nontrivial in the alloyed core system of ZCIS. Consequently, the improvement of QY is attributed to the evolution of the electronic structures and the suppression of defect states. The understanding of optical features increases the application potential of CIS using the alloyed-core/shell structures of ZCIS/ZnS QDs with considerably alleviated concerns of toxicity.