Diffused junctions in multicrystalline silicon solar cells studied by complementary scanning probe microscopy and scanning electron microscopy techniques

Abstract

The junction location in textured n+-p multicrystalline Si solar cell devices is quantitatively located. A comprehensive comparison is presented between secondary ion mass spectrometry (SIMS) and three microscopy techniques: scanning capacitance microscopy (SCM), scanning Kelvin probe microscopy (SKPM), and secondary electron contrast (SE) in the scanning electron microscope. The comparison includes capabilities of junction allocation, applicability of the measurement to give a two-dimensional analysis of a textured device, apparent imaging of the depletion region, depletion edge and depletion width determination, sample structure requirements for the specific methods, ease of sample preparation, and data acquisition time for high-quality measurements. We find that SE not only allows the most straightforward sample preparation and provides the quickest measurement, but also seems to show the depletion edge and width with a high degree of accuracy. This is verified by a comparison to PC1D simulations of the band bending in the bulk of the device. These data also contribute to our understanding of the origin of SE doping contrast. SKPM provides reliable junction identification but poor capability in determining the depletion width. All three techniques are able to show how well the diffused n+ emitter region tracks the surface topography, with SCM and SE yielding the clearest images.