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Today, solar cell substrates (panels) enter high vacuum and high temperature chambers and exit after all solar thin films are deposited, typically after one or a couple of hours. It is typical to have 15-40 solar panels moving inside the manufacturing line at a given time.

It is essential to be able to detect any deviations from the film's target parameters as soon as they occur in real time in order to correct these deviations for the same panel. Most available control solutions, such as XRF, Raman scattering, ellipsometry, and photo- and electroluminescence provide results too late and in most cases after the layer is already deposited.

Our patented control system is based on miniature fiber optic sensors installed at many specific points in existing equipment without disrupting the manufacturing process. It works with both stationary and moving panel configurations.

In its manual mode of operation the system displays all major film parameters during the film deposition and, in case of deviation, proposes adequate corrective actions to the operator. The list of displayed parameters is user reconfigurable and includes:

• Film thickness at different spots on the panel and film thickness uniformity over the panel

• Deposition rate and its difference between monitored spots

• Optical constants n&k, their change during deposition and their homogeneity in depth of the film

• Optical constant uniformity over the panel area

• Film material bandgap, its change during deposition and its homogeneity

• Bandgap uniformity over the area of the panel

• Film relative density compared to the intended material density

• Film porosity, potential water content and related lifetime implications

• Film optical scattering and its uniformity

• Haze and its uniformity

• Film surface roughness and its uniformity over the panel area

In its automatic mode of operation the system takes immediate corrective action as soon as deviations are detected. The software performs minor real-time re-optimization of the remaining part of the thin film sequence in order to accept the detected error as if it were pre-designed (“soft” correction)If no soft solution is available, the system may change some process parameters (such as deposition time temperature, power levels, etc.

Our thin film monitoring software is the brain of the system, which deploys novel data processing and optimization concepts based on our proprietary calculation and implementation schema. The system reports to the operator how the most important PV parameters are changing in time and over the area of the panel, or communicates to the machine controls directly in real time.

Since the sensors are positioned at many different locations along the manufacturing line and are controlled by the same software program, the system is able to automatically guide the thin film formation process (similar to the modern aircraft's autopilot), even as the parameters such as pressure, temperature, gas flow, currents, and other deposition parameters fluctuate or drift throughout the process. The solar panels always come out of production optimized with better efficiency.

AccuStrata does not replace the control systems, which are already installed by the equipment manufacturer and are in use, but adds one more layer of control, which typically takes care of all minor deviations during the process. This system eliminates unnecessary test runs and in some applications the point-to-point diagnostics and run-to-run control. It molds the product in real time by keeping it always focused on the product specification.