Porosity control in thin film solar cells

Abstract

This work focuses on the simulation and control of a porous silicon deposition process used in the manufacture of thin film solar cell systems. Initially, a thin film deposition process is simulated via a kinetic Monte Carlo (kMC) method on a triangular lattice following the model developed in Hu et al. (2009). Then a closed-form differential equation model is introduced to predict the dynamics of the kMC model and the parameters in this model are identified by fitting to open-loop kMC simulation results. A model predictive controller (MPC) is also designed and implemented on the kMC model. Extensive closed-loop simulation results demonstrate that both film thickness and porosity can be regulated to desired values. Finally, the porosity control framework is extended into a two-stage dual porosity deposition process, with two different porosity set-points for each stage. The closed-loop results demonstrate that at the end of both stages the film porosity values can be successfully regulated at the requested set-point values.