Surface potential investigation on interdigitated back contact solar cells by Scanning Electron Microscopy and Kelvin Probe Force Microscopy: Effect of electrical bias

Both Kelvin Probe Force Microscopy and Scanning Electron Microscopy enable assessment of the effect of electrical bias on the surface potential of the layers of a solar cell. We report on a comprehensive comparison of surface potential measurements on an interdigitated back contact solar cell using these two techniques. Measurements under different values of electrical biases are performed on and between the metallic contacts. They show a good agreement between the surface potential obtained with Kelvin Probe Force Microscopy and the Scanning Electron Microscopy signal. In order to provide an accurate comparison, the scanned areas are adjacent to each other and accurate repositioning is achieved thanks to a nano-indentation between the contacts. We show that measurements under reverse bias are of interest to locate nano-defects and measurements under forward bias are relevant to identify local series resistance issues. We suggest that a setup combining Scanning Electron Microscopy and Kelvin Probe Force Microscopy under different values of the electrical bias should be valuable since the former is a high throughput technique enabling measurements on large scan areas, while the latter is a quantitative, low noise, and unintrusive local technique.