Transforming organic ligands into a ZnS protective layer through the S2- intermediate state in ex situ CdSe quantum dot devices

Abstract

In this paper, the tri-n-octylphosphine oxide (TOPO) ligand on CdSe quantum dots (QDs) are changed to ZnS coating layer through S2- intermediate state. After ligand exchange, the Fourier transform infrared (FTIR) spectra indicate that the long chain organic ligands are replaced by S2- ions. After ionic reaction, the generation of ZnS is confirmed by X-ray photoelectron spectroscopy (XPS) measurements. In addition the UV-Vis absorption peaks did not move and transmission electron microscopy (TEM) results show that the diameters of the quantum dots decrease. Electrochemical impedance spectroscopy (EIS) results show that the interface resistance between the TiO2/QDs/electrolyte is reduced under illumination conditions, meaning that forward electron transport was enhanced. In addition, the intensity- modulated photovoltage spectroscopy (IMVS) and intensity- modulated photocurrent spectroscopy (IMPS) results reveal an increase in the electronic lifetime and diffusion rate increased. Finally, the conversion efficiency increases by 1.78 times from 0.98% (TOPO ligand) to 1.75% (ZnS coating). © Editorial office of Acta Physico-Chimica Sinica.