Interfacial passivation mechanism of sulfide towards quantum dot-sensitized nanocrystalline thin films.

We report on the interfacial passivation mechanism in CdSe quantum dot-sensitized ZnO nanocrystalline thin film, where different sulfide semiconductors (such as ZnS and CdS) and sulfide ions are used to modify ZnO nanocrystalline thin film before deposition of CdSe quantum dots (QDs). It is noticed that the highest light-to-electric conversion efficiency of CdSe quantum dot-sensitized ZnO nanocrystalline thin film solar cell is attained up to 4.18 % after CdS interfacial modification. Meanwhile, a simple treatment of ZnO nanocrystalline thin film in NaS solution can also increase the conversion efficiency of CdSe quantum dot-sensitized solar cell up to 3.45 %. The electron transfer and recombination processes occurred in the interface of QD-sensitized nanocrystalline thin films with and without the different interfacial modifications are detected by measuring intensity modulated photovoltage spectroscopy and electrochemical impedance spectroscopy of solar cells. These results indicate that adsorption of S ions on the surface active sites of ZnO nanoparticles is the main reason for the conversion efficiency improvement due to the interfacial passivation of sulfide semiconductors. [ABSTRACT FROM AUTHOR]