Micro cracks distribution and power degradation of polycrystalline solar cells wafer: Observations constructed from the analysis of 4000 samples

Abstract

In this paper, the impact of Photovoltaic (PV) micro cracks is assessed through the analysis of 4000 polycrystalline silicon solar cells. The inspection of the cracks has been carried out using an electron microscopy, which facilitate the detection of the cracks though the acquisition of both Everhart-Thornley Detector (ETD) and the Back Scatted Electron Diffraction (BSED) image, where it was found that the size micro cracks are ranging from 50 μm to a maximum of 4 mm. Micro cracks have been categorized into two main categories, including cracks in the solar cell front or rear contact. Several remarkable observations have been found, including but not limited to, (i) the output power loss due to micro cracks varies from 0.9% to 42.8%, subject to micro crack type and size, (ii) cracks in solar cells fingers reduce the finger width, resulting an increase in the output power loss by at least 1.7%, and (iii) there is a substantial correlation between PV hot-spots and the presence of micro cracks, while minimum increase in the cell temperature is observed at 7.6 °C.