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PERC cell inspection

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Currently the most economical solar cell design, the so-called PERC cells (passivated emitter and rear contact) can now individually be inspected with the highest contrasts. A new inspection system from Isra Vision takes on the challenge of inspecting the cell’s rear side. With its exclusive multi-channel and multi-image technologies, it merges high contrast image parts for a perfectly clear final picture. By allowing for pre-defined pattern shapes to be detected, the toolset avoids pseudo defects and minimizes the slipping rate in PERC inspection. Solar cell manufacturers therefore receive an easy to operate and highly cost-effective way to push the efficiency of their production.

The solar industry is picking up interest in PERC-technology with accelerating pace, with the cell design expected to become the new standard in photovoltaic production. In the construction of a “passivated emitter and rear contact”-cell, a dielectric passivation layer of Aluminum Oxide and Silicon Nitride ensures the most efficient use of incident light. After placing the passivation on the back of the cell, a laser opens the contact points, at which the rear metallization should touch the silicon wafer. These laser openings in micrometer scale are critical for the efficiency of a cell and can be analyzed in detail with post laser inspection. Having printed the Aluminum layer on top and finished the cell by firing it with high temperatures, the laser openings again become visible through the thin metal layer. This challenges the inspection of the cell’s rear side during the optical quality classification process. Pseudo defects or previously unnoticed print defects result in unsatisfactory classifying and cause avoidable costs for rework and material.

Multi-color illumination for best contrasts and results

While most competing systems often try to reach full contrasting on PERC using red or white lighting, the multi-channel technology deploys multiple illuminations with different wavelengths. This supports the best and most stable contrasts by spectral imaging and allows users to ignore slight color variations or gradients. By combining the information resulting from the varying types of illumination, ISRA VISION / GP SOLAR multi-image technology computes the most informative picture achievable. The result is that users only experience sharply defined contours of a contact or defect. The original color of the individual coating surrounding relevant spots becomes unimportant.

Easy definition of print patterns and shapes through pattern editor

Beyond that, the PERC inspection technology is supported by a flexible CAD-style editor to define any arbitrary contact shape for the rear side, similar to the print pattern editor for the front side. This allows for individualized inspection and the fastest implementation on site. Customers therefore can avoid investing additional programming or R&D efforts. The editor saves the specified patterns and allows for transferring them between different production lines and manufacturing sites. Besides the printing design pattern, each individual inspection job with its error tolerances and defect classes is also a part of the recipe. This ensures an easy ramp up of new production lines and allows for unitary quality standards of a cell type in all of a manufacturer’s plants and subsidiaries worldwide. The multi-channel and multi-image technologies are two of the novelties ISRA VISION / GP SOLAR delivers for photovoltaic inspection. With several extensions, the technologies pooled as CHROME+ are a breakthrough for innovative inspection in the solar industry. They enable all manufacturers to conduct efficient quality surveillance in production steps and end control to maximize cost efficiency and yield. With its comprehensive portfolio of inspection technology, ISRA VISION / GP SOLAR offers the most suitable solutions from wafer inspection to the final cell, for all new cell designs.

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