Liquid carbon dioxide coating of CdS quantum-dots on mesoporous TiO2 film for sensitized solar cell applications

Abstract

CdS quantum dots (QDs) were uniformly deposited on mesoporous TiO2 films by high-pressure coating with liquid carbon dioxide (l-CO2) as a coating solvent. The size and coverage of CdS QDs over the TiO2 surface were controlled by the number of l-CO2 coating cycles applied at a fixed precursor concentration. The formation of CdS QDs on the mesoporous TiO2 film was confirmed by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM). In addition, depth profiling investigation revealed that CdS QDs were uniformly deposited throughout the ∼15μm-thick mesoporous TiO2 film. The energy conversion efficiency of a CdS QD-sensitized solar cell (QDSSC) was observed to increase up to ∼1.33% under standard conditions (1.5AM, 100mWcm−2) with an increase in the number of coating cycles to six. Meanwhile, a further increase in the number of coating cycles to ten caused a decrease in the cell performance, which may be attributed to the hindrance of electrolyte infiltration into the mesoporous TiO2 electrode caused by the blocking of the pores with the coated CdS. The cell performance of the l-CO2-coated CdS-QDSSC is slightly higher than that of the l-CO2-coated CdS-QDSSC prepared by a conventional successive ionic layer absorption and reaction (SILAR) method with ethanol as the solvent (1.16%).