CIGS Photovoltaic Cells
While most solar photovoltaic cells are based on crystalline silicon technology, thin film solar cells based on Cu(InGa)Se2 (CIGS) have been demonstrated to achieve very high (~20%) energy conversion efficiency. Furthermore, this technology lends itself to manufacturing techniques that are much less costly than conventionally processed silicon. While worldwide production of CIGS cells is ramping up, the cell efficiency that is achieved on the production lines is about half of the efficiency of cells produced in the lab. Extensive research has been conducted in an effort to overcome the issues associated with scaling the manufacturing process of these cells. My research will continue this branch of research by increasing understanding of the plume dynamics for the effusion sources.
The concentration of materials used must be tightly controlled in order for the correct phase of material to grow on the substrate. Furthermore, the thickness of the deposited film needs to be controlled in order to obtain optimal electrical properties. Understanding of the gas dynamics involved with the source plumes can also result in higher throughput and yield and better material utilization.
The Direct Simulation Monte Carlos (DSMC) method will be employed to characterize the flow since the flow is considered non-continuum. DSMC is a statistical approach to modeling flows. The method uses probability functions to calculate the macroscopic properties of the gas based on microscopic properties of representative sample molecules. Needless to say, when tens of thousands of molecules participate in a flow the calculation is computationally expensive. In fact, computer clusters are used to model a flow and the computation can take several hours if not days. This approach can provide detailed insight in the dynamics of effusion plumes. Ultimately, this understanding can be used to develop physical-based reduced-order algorithms for process control.