Aqueous synthesis of CdTe-CdS core shell nanocrystals and effect of shell-formation process on the efficiency of quantum dot sensitized solar cells

Abstract

In this research CdTe nanocrystals (NCs) were synthesized in aqueous solution through a hot-injection chemical precipitation method. Then a shell formation process was carried out to form CdTe-CdS NCs with different shell thickness. Thioacetamide was applied as a thermo-sensitive source of S and the shell making time was altered in the range of 0–120 min. different core-shell CdTe-CdS NCs were utilized for co-sensitization of the photoanode of the quantum dot sensitized solar cells (QDSCs). These photoelectrodes were pre-sensitized by CdS NCs deposited on a transparent mesopous TiO2 scaffold with specific thickness. The effect of shell formation time on the photovoltaic (PV) performance of the corresponding cells was investigated. The photovoltaic parameters were quite reduced for the QDSCs sensitized by CdTe-CdS NCs prepared in short shell-formation times. Then the PV performance was considerably improved and reached to its maximum for the cells with sensitizing QDs with higher shell thicknesses. The corresponding performance was finally decreased for the co-sensitization with core-shell NCs synthesized in longer shell-making times than 100 min. A maximum power conversion efficiency of 4.2% was achieved for the co-sensitized QDSC with CdTe-CdS NCs prepared in 80 min of the shell-formation process. This efficiency was enhanced about 91% compared to the reference QDSC with TiO2/CdS/ZnS photoanode. The trend of changes in PV performance was explained based on the flat-band energy diagram of the QDSCs and permitted transitions for the electrons and holes in different shell thicknesses.