Here we report on a novel method, which allows rapid photoluminescence imaging of band‐to‐band and dislocation‐related radiation, D1, on multicrystalline silicon wafers at room temperature. We demonstrate spatially resolved 5.0 × 5.0 cm2 D1‐images, with a resolution of ∼120 µm, within a total recording time of 550 ms. The method provides homogeneous illumination over the whole sample area. Comparison with results from a conventional photoluminescence mapping technique demonstrates the potential of this new method for application as an in‐line wafer characterization technique.
We report on a method for fast detection of defect rich areas in multicrystalline silicon solar wafers. It is based on photoluminescence imaging of the whole wafers and detects both the band‐to‐band radiation as well as the dislocation specific radiation D1. To illustrate the capabilities of the method we examined 5.0 × 5.0 cm2 wafer pieces in different stages of their processing. The achieved resolution of the D1 images was ∼120 μm, within a total recording time of 550 ms.
We studied the correlation between the appearance of defects and of breakdowns in fully processed solar cells by electroluminescence imaging. Images under forward and reverse bias were recorded, revealing defective areas and breakdown sites of the cells, respectively. In the experiments presented here an InGaAs camera system was used, which allows us to detect short wave infrared light in the 900–1700 nm range. Applying a forward bias the band‐to‐band luminescence (1.1 eV/1150 nm) and the defect‐related luminescence (0.8 eV/1550 nm) were imaged. Both imaging techniques reveal mainly dislocation‐rich areas and grain boundaries. Applying a reverse bias (approximately −10 V), breakdown luminescence occurs. It was found that the distribution of the breakdown sites across the solar cells is different from the distribution of the defects showing luminescence at 0.8 eV (grain boundaries, dislocations). The spatial separation between those defects and the breakdown sites was clearly evidenced by high resolution imaging. Possible reasons for such spatial separation are discussed.
We report on 0.93 eV luminescence observed in multicrystalline silicon. The spectral line is close to the well known D3 one, but its properties are different. The new feature shows a remarkable intensity at room temperature, exceeding the intensity of the band to band radiative transition. Moreover, it appears as a single line in the entire temperature range 10-300K, in contrast to the D3, which is usually accompanied by D4. Cathodoluminescence (CL) and electron beam induced current (EBIC) micrographs revealed that the centers causing 0.93 eV emission are irregularly distributed along certain grain boundaries. Electron backscattering diffraction examination showed that the 0.93 eV luminescence appears at grain boundaries characterized by a lattice rotation around a <344> axis. The EBIC contrast at those irregularities indicates strong total recombination. Based on an analysis of the temperature dependence of the CL intensity and the EBIC contrast we obtained an activation energy of about 120 meV.
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