Introduction To Ultra-high Vacuum Thermal Evaporation System And Preparation Of CdS Thin Films

CdTe/CdS thin film solar cells because of the high theoretical conversion efficiency, as well as efficient, stable, cheap and so on, is currently the most talked about film photovoltaic devices materials. A Typical CdTe/CdS thin film solar cell is composed of a heterojunction with N-type CdS layer and P-type CdTe layer. CdS thin film, as N-type semiconductor layer and window layer in solar cell, its quality would directly affect the absorption layer which is prepared on the basis of it and is very important to the efficiency and lifetime of the batteries. Vacuum evaporation is belonging to physical vapor deposition (PVD), has several decades of development history, and is widely used in many scientific and technological fields. In the high vacuum environment, average free path of the vapor molecule is great, and the mutual collision probability is greatly reduced. Therefore, the thin film growth under such conditions will possess some special performance. In order to carry out the preparation growth of CdS thin films better, it is necessary to understand the structure of the ultra-high vacuum thin film evaporation system, the working principle of the various components, as well as the debugging process of using of various parts in-depth. At the some time, to study the impact of the preparation conditions on the crystalline structure, surface morphology and optical properties of CdS thin films is of great significance to improve the conversion efficiency of the battery. This thesis include:1. An introduction to the vacuum thermal evaporation thin film growth system. First, the K09-007ultra-high vacuum thin film evaporation system was described in detail from the gas system, pumping system, vacuum measurement systems, heating control system. Second, it presented the working principle of reflection high energy electron diffraction and its debugging process of using. Some experimental results of silicon surface was given, and the basic parameters of the instruments was calculated from the diffraction pattern of silicon surface, which can be used to measure the lattice constant of other crystal materials.2. Investigation to the preparation conditions of CdS thin film. The K09-007ultra-high vacuum thin film evaporation system was used to prepare two series of CdS thin films under different preparation conditions, one was prepared under different growth pressure and the other was under different substrate deposition temperature. The structure, morphology, optical characteristics, electrical properties of CdS thin films were characterized by atomic force microscopy, X-ray diffraction (XRD), UV-visible-infrared spectrophotometer, four-point probe system, Hall effect measuring instrument, etc. The influence of the preparation conditions to the properties of the CdS thin film was studied.