Designing a low cost camera to analyse defects in photovoltaic cells with the forward and reverse bias electroluminescence method

Abstract

The department of solar energy in the Faculty of Electrical Engineering and Communication (FEEC) in the Brno University of Technology (BUT) performs research on the detection of defects in solar cells using the electroluminescence method. This method currently uses an expensive astronomy CCD camera that is not robust enough to withstand the handling of students. This master's thesis focusses on the comparison of the forward and reverse bias electroluminescence method to detect the different defects in solar cells. Meanwhile a cheap alternative camera is developed and built for students to experiment with.

Firstly, analysing both versions of the electroluminescence method and the currently known defects in solar cells is done by a literature study and with the MATLAB image processing toolbox. Secondly, a comparison between the upcoming CMOS technology and the already well-established CCD chip is performed to define the optimal choice. Lastly, the internal IR blocking filter from a commercial CCD camera with an optimal spectrum is removed to allow all wavelengths to pass through to the sensor.

The forward bias electroluminescence proves to be valuable for both monocrystalline and polycrystalline silicon solar cells as it can visualise most of the known defects. The reverse bias electroluminescence on the other hand proves to be unreliable for monocrystalline as it's unable to detect silicon-growth defects but it's equally effective for polycrystalline silicon solar cells.