In this work CdTe NCs with different sizes were synthesized through a hot-injection chemical precipitation method. Then they were applied as the co-sensitizers in the photoelectrode of the CdTe and CdS sensitized solar cells. The photoelectrodes were composed of a nanocrystalline TiO2 layer formed of hydrothermally grown TiO2 NCs with dominant size of 25 nm. This layer was sensitized with CdS and CdTe NCs via the successive ionic layer adsorption and reaction (SILAR) and drop casting methods. The average size of utilized CdTe NCs was altered in the range of 2.7e3.4 nm in the experiments. Polysulfide electrolyte and CuS counter electrodes were also applied in conventional structure of these QDSCs. Different photoanodes were fabricated with various sizes of the as prepared CdTe NCs. Then the effect of corresponding bandgap energies and band edge positions on the photovoltaic performance of the CdS/ CdTe sensitized solar cells was investigated. According to the results, a maximum efficiency of 3.8% was achieved for the QDSC with CdTe NCs prepared at 5h of refluxing process (3.2 nm). This efficiency was increased about 72% compared to the reference cell which was sensitized with just CdS NCs. The optimization was also addressed based on the energy band diagram of the composing components of the fabricated QDSCs.
