Research On Absorber Of Copper-Indium-Gallium-Selenium Thin Film Solar Cell

The Copper-Indium-Gallium-Selenium (CIGS) chalcopyrite material has attracted extensive interests due to its high absorption coefficient, good stability, strong ability of anti-radiation, adjustable optical band gap, etc. At present, the conversion efficiency of thin film solar cells based on CIGS polycrystalline thin films in laboratory has reached beyond 20%, and the CIGS solar cells are considered to be the most promissing thin film solar cells. In this thesis, the purpose of study is to prepare high-quality CIGS absorber and hence improve the performance of CIGS solar cells.In this paper, CIGS polycrystalline thin films were were deposited by using electron beam evaporation method and the multi-source co-evaporation "three stage" process. The monitoring method commonly used in optical thin films was innovatively applied in in-situ monitoring the composition and thickness of CIGS semiconductor thin films. Based on the electron-beam evaporation and light controlling method, we have investigated effects of substrate temperature of each stage, the thickness of thin film of the first stage, compositon of Cu and Ga, deposition rates, etc. in details on structrural, optical and eletrical properties of CIGS thin films and photovoltaic characteristics of CIGS solar cells. After systematic optimization of CIGS processing parameters, we found the best depostion condition for preparing high quality CIGS thin films by electron beam.The device performance of CIGS solar cells could be largely improved by incorporating Na into CIGS thin films. The common method for dopping Na is Na diffusion from soda lime glass substrate into CIGS absorber at high temperature during CIGS growth. Based on light controlling method, here we investigated the effects of evaporating NaF between different stages during CIGS deposition on CIGS thin films and solar cells. It is found that incorporating Na between the first stage and the second stage is the best way for dopping Na by co-evaporating NaF. By this method. CIGS thin film with high quality has been prepared.During investigation of depositing ZnS buffer layer by electron beam, we found that the ZnS vpoar has sulfurization-effect on surface layers of CIGS thin films in case of relatively high substrate temperature, we explained this phenomenon and systematically studied the effects of ZnS evaporated by electron beam on CIGS thin films. Device parameters of CIGS solar cells with the ZnS post-depostion treatment were largely enhanced, thus a new method for surface sulfurization of CIGS thin fims was successfully proposed, which is more advantageous than the current methods for surface sulfurization using H2S gas or S vapor within laboratory scale.We have systematically investigated the effects of In-Ga-Se thin layer post-deposited at different temperatures on CIGS thin films and solar cells, and proposed a method for adjusting Cu concentration in surface layer of CIGS thin film by post-depositing In-Ga-Se thin layer. After optimizing the substrate temperatures and thickness of thin films, a relatively high quality OVC surface layer was successfully fabricated, by which the performance of CIGS solar cells was greatly improved.