(747a) Control of Transparent Conducting Oxide Surface Morphology for Improved Light Trapping Using Wafer Grating and Model Predictive Control

Thin-film silicon solar cells are currently among the most
important and widely used solar
cell systems and their share of the overall solar cell market is steadily
increasing.
Transparent Conducting Oxide (TCO) layers are an important component of
thin film
solar cell system. It has been demonstrated by many researches that the
surface
morphology, which is characterized by aggregate surface roughness and
slope, has a
crucial influence on the light trapping process and the conversion
efficiency of
thin film solar cell systems. Thus, it is very important to control the
TCO surface
morphology properties at desired values during the deposition process to
improve the
performance of thin film solar cells.
This work focuses on the design of a feedback control system using both
wafer grating and a model predictive controller to shape
the surface morphology for improve solar cell performance. Specifically, a
sinusoidal grated wafer is used
for TCO thin film deposition process and a spatially distributed
deposition rate
profile is used to precisely control the TCO surface morphology during the
deposition process. In this work, an Edwards-Wilkinson (EW) type equation
is used
to predict the process dynamics and the analytical solution of EW equation is
derived as the basis of controller design. The model parameters of EW
equations are
identified by fitting the closed-form equation to open loop simulation
data obtained from large-lattice kinetic Monte Carlo
simulations.
Finally, the controller is applied to a large scale kinetic Monte Carlo
model of a TCO deposition process and the results demonstrate that the
controller
successfully regulates the surface morphology to desired values that lead
to improved light
trapping and solar cell performance.