Whether we're talking CIGS, CdTe, or a-Si – thin-film solar is a relatively new technology.
And as a young industry, there are still gaps in its complex manufacturing process.
"In-situ monitoring capability is truly a gaping hole in PV manufacturing," said a colleague at a stealthy CIGS firm.
AccuStrata, a small startup at the University of Maryland business incubator in College Park, Md. is looking to change this.
Thin-film solar manufacturers typically do not have real-time data about what is happening on the moving substrate as films are deposited inside deposition chambers. Legacy metrology tools usually measure the physical parameters of the films after the materials are already deposited. If process flaws are detected, the process parameters are tweaked to address the problem for the next production run. The result is low manufacturing yield and a waste of materials, energy, time, and money.
George Atanasoff, the President of AccuStrata referred to this as "post-factum monitoring."
AccuStrata is developing a real-time optical control system to improve the quality and increase the conversion efficiency of thin-film solar panels. The system is based on the firm's control software and small fiber optic sensors installed inside the thin-film deposition equipment. The system performs Real Time Spectroscopic Reflectometry and derives several important physical parameters of the films as they are being deposited, such as thickness and surface roughness, refractive index, lattice constant, absorption and scattering coefficients and film bandgap. The miniaturization of the sensors allow deployment of multiple sensors in parallel and in series configurations and monitoring the surface of the entire panel at different moments of deposition.
The constant collection of data allows the creation of "response surface models" used by the software to guide the manufacturing process “on-the-fly” and make each panel to meet its' target specification. The company refers to its system as a "solar panel manufacturing autopilot” with the intention of accruing this data into a sort of manufacturing expert system.
The company will soon be installing its first prototype system into a PV manufacturing line at a CIGS vendor you would likely recognize. CIGS players include names like Global Solar, Heliovolt, Miasole, Solyndra, and more than 30 others vying for the zero billion dollar CIGS thin-film PV market. AccuStrata looks to gain revenue from the sales of hardware, software and the replacement and maintenance of sensors.
The company is backed by its founders, angel investors, the State of Maryland, the NSF and is set to receive $150,000 in federal stimulus funds.
Other firms like Laytec and BT Imaging are also developing process control and metrology equipment for solar manufacturing.