Formation and Characterisation of CdSe-TiO2 Nanoparticle Films by Electrophoretic Deposition

Abstract

Electrophoretic deposition (EPD) was used to form a composite layer of mercaptoundeconic acid (MUA) capped CdSe-TiO2 nanoparticle on a fluorine doped indium tin oxide (FTO) substrate. The CdSe-TiO2 layer can be employed to fabricate a quantum dot sensitized solar cells (QDSSC), increased contact between CdSe and TiO2 nanoparticles and leading to improved efficiency of the solar cells. A colloidal suspension of TOPO capped CdSe nanoparticles was prepared by the hot injection method, followed with ligand exchange in order to produce MUA capped CdSe nanoparticles. CdSe particle of diameter in the range of 2.44 nm to 3.26 nm were to be used in this research. The TiO2 nanoparticles were prepared by hydrolysis of titanium isopropoxide in water and produced particles size of 4.66 nm. Both nanoparticles were suspended in ethanolic medium. Electrophoretic deposition parameters were optimized. The results show that an applied voltage of 5 V, was suitable to be used to deposit single layer of MUA capped CdSe, TiO2 nanoparticles and the mixture of MUA capped CdSe-TiO2 nanoparticles. Smooth, uniform and dense layer were produced under this applied voltage. EPD also allows deposition of multilayer structures, in this research two layer structures of MUA capped CdSe on electrophoretically deposited TiO2 on FTO and mixed MUA capped CdSe-TiO2 on electrophoretically deposited TiO2 on FTO were formed. Three layer structures of MUA capped CdSe/MUA capped CdSe-TiO2/ TiO2/FTO were also synthesised. The photocurrent was measured on single layer, two layer and three layers electrodes. The optimum photocurrent parameters for each single layer were studied, in order to measure the photocurrent at the best condition possible. The highest IPCE value recorder was 0.70 % on MUA capped CdSe on FTO, with the MUA capped CdSe size of 2.94 nm. The lowest IPCE, 0.011 %, was obtained from three layer structure of MUA capped CdSe/MUA capped CdSe-TiO2/ TiO2/FTO.