Photovoltaics

Photoluminescence (PL) inspection using shortwave infrared (SWIR) imaging offers a powerful, non-contact method for improving the quality and efficiency of photovoltaic (PV) manufacturing. Leveraging InGaAs-based SWIR cameras, this technique enables machine-vision systems to inspect silicon ingots, wafers, and fully processed solar cells. When materials are illuminated at a specific wavelength, they absorb and re-emit light based on their semiconductor properties. This emission is captured in real-time by SWIR cameras, revealing variations in material quality and processing performance, such as minority carrier lifetime, which directly affects solar cell efficiency.

SWIR PL imaging provides several key advantages over traditional electroluminescence (EL) or visible PL inspection. It is contactless, requires minimal sample preparation, and functions across multiple stages of production—including raw, partially finished, and backside-metalized wafers. Unlike EL, which needs electrodes, SWIR PL can detect defects early in the process. Additionally, SWIR systems offer high-speed imaging at video frame rates (up to 60 fps), whereas silicon CCD cameras often require long exposure times (up to 30 seconds).

Demonstrations using InGaAs SWIR cameras showed that even with lower resolution and shorter exposures, PL images captured more detail and defect visibility than those from high-resolution CCDs. The technology supports real-time, high-throughput inspection without disrupting production, making it ideal for 100% in-line monitoring. Experiments conducted with laser diode arrays and optical filters further confirm the effectiveness of SWIR imaging in capturing subtle variations in crystal growth and material uniformity, offering a major step forward in PV quality assurance and yield improvement.