Comparison of solar cells sensitised by CdTe/CdSe and CdSe/CdTe core/shell colloidal quantum dots with and without a CdS outer layer

摘要

CdTe/CdSe and CdSe/CdTe core/shell colloidal quantum dots, both with and without a second CdS shell, have been synthesised and characterised by absorption and photoluminescence spectroscopies, scanning transmission electron microscopy and X-ray diffraction. Each type of quantum dot had a zinc blende crystal structure and had an absorption edge in the near-infrared, potentially enabling the more efficient exploitation of the solar spectrum. Each was used to sensitise a photovoltaic cell of a 'Graetzel-type' design consisting of the dots coated onto mesoporous TiO_2, a sulphur-based electrolyte and a platinum top electrode. The photovoltaic efficiency of the cells was found to be greater for Type-Ⅱ dots as compared to the quasi-Type-Ⅱ dots. However, the efficiency was reduced on the addition of an outer CdS shell indicating that it acts as a barrier to charge extraction.