Microscale localization and detection of defects in crystalline silicon solar cells

The quality of a solar cell structure is one of the principal features determining its performance, lifetime and reliability. The defects from structural inhomogeneities or chemical impurities are the origins of non-ideal behavior, resulting in undesired loss of converted solar energy. Conventional macroscale inspection systems are able to detect and determine visibly-large defects that appear on the solar cell surface only. However hidden and small irregularities inside the cell or on its borders, e.g. almost invisible microcracks and tiny inhomogeneities, also considerably affect overall efficiency and lifetime of the solar cell. For our local investigation of these sub-micron irregularities in a monocrystalline silicon solar cell structure we use a combination of scanning near-field microscopy (SNOM) with electronic measurement. The experiments rely on the fact that silicon solar cells under reverse bias exhibit micron-scale low light emitting centers. A novel method allows a simultaneous localization and measurement of this light on microscale. The method also allows the characterization of these irregularities with high spatial resolution.