Studies On The Preparation And The Properties Of The CdS Quantum Dots Sensitized TiO₂ Photoelectrodes

Solar cells have reached much attention nowadays for its low cost, cleanness and endlessness. In this paper, the material and the structure of different kinds of the solar cells were expatiated. The relation of nano-material and the solar cells, the development of the solar cells and the problems in the solar cells were reviewed.As a kind of cheap and safe semiconductor material, TiO₂ has been extensively investigated in the filed of solar cells. But it can't absorb the solar radialization effectively for its wide band-gap. One way to solve this problem is to use arrow band-gap semiconductor material to sensitize it. CdS with the band-gap of 2.42ev is a typical semiconductor material to sensitize TiO₂ electrodes. Many researchers now are interested in quantum dots sensitized TiO₂ solar cells. However, nano-particles with quantum dimension are inclined to reunite. To solve the problem, in the present study, the conducting polymer (SPAn) was employed to pack the nano-particles to avoid reuniting. At the same time, the self-assemble method was used to graft the CdS nano-particles to the TiO₂ porous films.Three main parts were involved in the study: the synthesis of SPAn/CdS nano-particles is introduced in the first part, the synthesis of CdS nano-particles of quantum dimension is depicted in the second part and the investigation of the TiO₂/CdS electrodes is presented in the last part.SPAn/CdS nano-particles were prepared by the hydrothermal method. The effects of the content of the SPAn, the reacting time, the reacting temperature and the solvent were investigated. Results show that the system with SPAn added can prevent reuniting effectively. But the size of the SPAn/CdS nano-particles is much lager than the quantum dimension of the CdS, which restrict its use to sensitize the TiO₂ electrodes.The CdS nano-particles prepared by hydrothermal method in microemulsion without conducting polymer were also investigated. The results show that the diameter of the nano-particles decreased with the increase of the molar ratio of thewater and cyclohexane. The minimum diameter of the nano-particles is below lOnm. The size of the CdS nano-particles prepared by hydrothermal method with PH>7 is below 6nm.The CdS quantum dots were grafted to the porous TiC>2 porous films through the bridge of mercaptoacetic acid. The UV-VIS absorption spectrum and the I-V curve were also investigated. The results show that the CdS quantum dots can enhance the photocurrent effectively. The photocurrent increased with the decrease of the quantum dots size. The largest photocurrent of the electrode with CdS quantum dots sensitized is twice higher than that of the electrode without sensitization. This can contribute to the absorption of the CdS at the visible light and the quantum effect of the quantum dots.