Local investigation of thermal dependence of light emission from reverse-biased monocrystalline silicon solar cells

The quality and lifetime of solar cells critically depend on minimization of both bulk and surface imperfections. When a solar cell is reverse-biased with low voltage, weak emission from imperfections (pre-breakdown sites) appears. We report on the local measurement of such breakdown using a scanning near-field optical microscope. Due to the very weak signals, we use a cooled photomultiplier in the photon counting regime to achieve high sensitivity light detection. This technique allows non-destructive detection, localization and high spatial resolution of light-emitting centers originating from different imperfections in the cell. We have found that the emission from these pre-breakdown sites exhibits unique thermal characteristics. As a consequence, the thermal characteristics can distinguish among several kinds of imperfections in monocrystalline silicon solar cells.

Graphical AbstractTwo kinds of defects in the bulk and near the edge of monocrystalline silicon solar cell and their thermal dependence of emission.Figure optionsDownload as PowerPoint slideHighlights
► Electrical and SNOM methods allow better localization of defects in solar cells.
► Defects are thermally dependent.
► Only 30 K temperature range is sufficient for the defect classification.