Novel evaluation of intra-grain defects in polycrystalline silicon solar cells using light emission

The intra-grain defects in polycrystalline Si solar cells were detected for the first time by photographic surveying of light emission from the cell under reverse bias. Emission in visible wavelength region was induced by the hot carriers excited by high electric field surrounding the intra-grain defects. Size and distribution of the defects could be analyzed photographically. The distribution of the bright-spots in the emission photograph was corresponded to the dark areas (i.e. the intra-grain defects) observed by the conventional electron beam induced current (EBIC) and the laser beam induced current (LBIC) methods. The visible wavelength light with a broad spectrum was due to the intra- and inter-band radiative transitions. This photographic surveying method is readily effective to detect the electrically active defects such as the intra-grain defects without any probing tools.