Development of Advanced Process for the Fabrication of High-Efficiency Cd-Free CIGS Solar Cells

Thin film solar cells will consume a little of material and have potentials in low cost, mass production and flexible substrate applications. The most interesting substrates are steel foils, since they can be coated in a roll-to-roll process at high temperatures of up to 600°C in a Se atmosphere. In the last few years, thin film solar cells draw people’s attention due to their great potential application in the future. The Cu(In, Ga)Se2 (CIGS) research teams in Chang Gung University propose a project including seven subprojects to promote the efficiency of CIGS solar cells. This project will cooperate with Nanya Plastic Corporation in developing vacuum and non-vacuum process to fabricate high-efficiency and large-area CIGS solar cells. It is known that a very high efficiency can be achieved by vacuum process with co-evaporation techniques. However, it suffers high cost and large-area uniformity problems. A non-vacuum process with chemical coating has the advantages of low cost and large area capability. In addition, Nanya Plastic Corporation has a very good technique on coating process. Based on Nanya’s expert experiences, this project will focus on chemical coating process to fabricate CIGS solar cells. However, a vacuum process with sputtering techniques is also studied for intermediate phase processing evaluation. This process technology developed by this project will provide important information to for evaluating to fund for a new company to manufacture CIGS solar cells. To successfully fabricating high efficiency CIGS solar cells, many processing parameters should be taken carefully. The goal would be not attainable if they do not carefully process. We plan seven sub-projects to accomplish the mission goal. The first subject focuses on the study of process parameters for flexible CIGS substrates. The second and third sub-projects investigate how to prepare a very good CIGS absorber layer. A vacuum process with sputtering and selenization are used to fabricate a CIGS absorber layer in the second sub-project. The third sub-project prepares a CIGS absorber layer by non-vacuum process with a chemical solution coating technology. The CdS buffer layer has a pollution problem. A Cd-free buffer for CIGS solar cells is developed in the forth sub-project. The ZnO(i) and ZnO:Al transparent conductive films are investigated by vacuum process in the fifth sub-project and non-vacuum process in the sixth subject. The seventh sub-project is to study the fabrication of ZnO nanotip arrays as antireflection layer to replace traditional MgF2 antireflection layer. In main project work, the integrated optimization of these processes is studied. It is believed that a high efficiency CIGS solar cell can be achieved by integrating and optimizing these process parameters. In the three-year project, our mission goal is to achieve a solar efficiency higher than 8%(sputtering and selenization) and 3%(chemical solution coating) in the first year, higher than 10%(sputtering and selenization) and 8%(chemical solution coating) in the second year and higher than 14%(sputtering and selenization) and 12%(chemical solution coating) in the third year.

Project ID:PB9901-0246
External Project ID:NSC98-3114-E182-001-CC2