Photovoltaic inspection

Photovoltaics (PV) has grown into a substantial industry, with annual revenues in 2020 estimated to be more than $75 billion and expected growth to exceed $110 billion by 2025.

 

Laser-based techniques in photovoltaic inspection reveal a variety of material properties and are used extensively throughout the industry. Measurements such as surface reflectance, deep level traps, carrier diffusion, crystalline structure and boundaries, junction type depth and temperature, optical absorption and scattering, and photon degradation all have an influence on the efficiency of the solar cell and can be measured via a series of optical processes.

Most photovoltaic manufacturing is in silicon; however, researchers are looking for lower cost, higher efficiency alternatives – for which perovskite is of interest.

Power conversion efficiency of perovskite solar cells has shot up from under 4% to almost 30% over the past decade, generating much excitement. A small volume of perovskite material can generate the same amount of solar power as several tons of silicon. As a direct bandgap semiconductor, perovskites are well-suited for solar cells.

Perovskite is affordable, sustainable, efficient, and has the potential to outpace silicon in the photovoltaics market. However, perovskite efficiency has only been measured on tiny samples and is not yet commercially viable.

Single frequency lasers provide an efficient, contactless replacement to costly lithographic steps and, with the correct laser characteristics and wavelengths, these sources can also inspect, alter, and activate these novel materials. Achieving high production yield at lower cost requires sources with high spatial resolution, excellent beam quality, and long-term power stability.

For example, photoluminescence (PL) imaging can be used for both outgoing quality control (wafer makers) and incoming quality control (cell makers), where Near-Infrared (NIR) lasers are often used as a cost-effective light source for this purpose.

 
Laser sources in the ultraviolet (UV) range offer flexibility over both the material characterization and processing steps. As in semiconductor processing, UV light is used in a variety of measurement steps and techniques for photovoltaic cell inspection, where shorter wavelengths allow for analysis on increased surface complexity and high-power UV sources radiate or ablate degraded materials on the substrate barrier.

Skylark develop and manufacture single frequency laser sources from the NIR to UV range, with characteristics designed for their suitability in these optical processes.

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1. Beam quality
Beam quality includes laser beam size, shape, stability, and intensity. Single transverse mode beams (TEM00) are vital for the characterization of PV cells, allowing for high spatial control. Excellent beam shape, stable pointing and low ellipticity maintains consistency in processing and inspection.

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2. Low noise
PV cell and wafer inspection lasers must emit low noise to minimize detection errors and prevent inaccuracy in the characterization. Low noise level, in combination with narrow linewidths, increases the signal to noise ratio and enhances measurement and inspection sensitivity.

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3. Stability
To ensure consistency from cell to cell and panel to panel, laser sources also require exceptional spectral and power stability for high-resolution measurements and the elimination of errors in prolonged measurement.