A microanalytical study of aluminium diffusion in photovoltaic cells using imaging-mode laser-induced breakdown spectrometry

Diffusion of aluminium in solar cell fingers into the silicon bulk has been studied using imaging-mode laser-induced breakdown spectrometry (LIBS). The focused beam of a pulsed N2 laser (337.1 nm) was used to create a microplasma on the target surface. Due to the beam profile of the nitrogen laser, the resulting crater had an elliptical shape. Subsequent plasma optical emission of the plasma was spectrally and spatially resolved and detected with a non-intensified charged-coupled device detector. A total area of 3×2.5 mm2 has been sampled with a lateral resolution of 50 μm in the minor direction axis of the elliptical crater. Chemical maps of aluminium and silver are shown. Depth maps of aluminium diffusion for different lateral positions in the sample have been obtained. The capability to distinguish between the diffused aluminium and that belonging to solar cell fingers is demonstrated by using a simple mathematical algorithm in the post-processing of the spatially resolved spectral data. The results show the capabilities of LIBS to provide rapid and simultaneous multielemental chemical imaging of silicon materials.