The Surface Adsorption And Doping Of ZnO

In recent years, the dye-sensitized nanocrystalline solar cells has aroused widespread concern because of its low cost and high efffciency as the energy issues become increasingly prominent. The dye molecules are usually adsorbed on the surface of the nano-semiconductor thin film in the form of chemical adsorption, the battery will be oxidized and reduced when it works, And the working battery will produce lots of heat, which can easily lead to the shedding of the dye molecule and affect the performance of the battery. In addition, the dye molecules excited by the sunlight will generate the electrons which transmit to the nano-film substrate firstly,and then transmit to the external circuit from the base,so a current loop is formed eventually. If the electrons are able to rapidly transfer or not determines the efficiency of the battery directly. Increasing the adsorption stability of the dye molecules and improving the transmission rate of the electron in the battery are helpful for preparing the dye-sensitized solar cells which are more efficient and more stable. Therefore, the dye-sensitized nanocrystalline solar cells are studied based on the first-principles of the density functional theory from the following two aspects in this paper:(1) The ZnO surface adsorption and adsorption mechanism of the five kinds of fixed groups which are-CN,-NH2,-OH,-COOH and-SH in the dye molecules are studied. The results are showed as follows:5kinds of groups in the ZnO surface occur the chemical adsorption, three of them which are-CN,-NH2and-OH occur the non-dissociative adsorption, the rest of them which are-COOH and-SH occur the dissociative adsorption.The adsorption energys of the fixed groups are-0.64eV,-1.28eV,-1.03eV,-1.21eV (-1.40eV) and-1.14eV, respectively. In summary, the dye-sensitized solar cells (DSSCs) which are prepared by the dye molecules of the fixed group-COOH have a more stable performance, and they also have a maximum electron transmission rate. This provides a theoretical basis for the design and application of ZnO dye-sensitized solar cells.(2) In order to increase the transmission speed of ZnO electron and-improve the efficiency of the dye-sensitized solar cell, Ga, N and Ga are selected to study the n-type doped and p-type doped of ZnO (2x2x1) superlattice, the energy band structure, the electronic total states density and the partial wave states density are analyzed. The study results are showed that:1) via the Ga-doped, n-type ZnO can be achieved, and the electrical conductivity of ZnO can be enhanced. However, when the doping concentration is greater than0.02, its conductivity decreases with increasing the doping concentration.2) It is difficult to obtain the stable p-type ZnO semiconductor via the single N-doped, p-type can be achieved via N and Ga-doped, and it has good electrical conductivity. But the nonlocal characteristics of2N-Ga-doped are more obvious than the N-Ga-doped, which can improve the concentration of the carriers and prepare more quality p-type ZnO material.