High-resolution Optical and Electro-optical Microscopy for PV-modules

Non-destructive methods for high-resolution inspection are of great importance for quality assurance, reliability assessment and for research and development. Especially for samples like solar modules or large specimens high-resolution microscopy measurements are not used and therefore observable details are strongly limited by the optical resolution. Small defects can grow and cause a reduction of the module's lifetime. A portal-based inspection system has been set up for large samples like a PV-module or any other large sample. It can be equipped with several optical systems like cameras or a microscope. The optical properties are optimized for visual or for electroluminescence imaging on a macroscopic and microscopic scale and complements an existing Dark Lock-In Thermography (DLIT) setup for modules.The inspection system has been exemplarily used on two samples with defects and degradations to elucidate the wide range of applications. An investigation on a module with snail trail discolorations has been conducted. Cell cracks, finger interruptions and finger discoloration are measured using light microscopy and micro-electroluminescence imaging (μ-EL). Cracks within EL-inactive cell parts could be revealed only with light microscopy. On another sample the correlation on a microscopic scale of visible cell cracks, local delamination and the corresponding micro-electroluminescence (μ-EL) will be demonstrated. The correlation of light microscopy, μ-EL and DLIT illustrates the potential of a high-resolution module inspection for quality control, reliability assessment and for research and development.