Admittance Measurements on a-Si/c-Si Heterojunction Solar Cells

Abstract

Hydrogenerated amorphous silicon/crystalline silicon (a-Si:H/c-Si) solar cells with areas of are produced by deposition of a-Si:H and indium-tin-oxide (ITO) on wafers. Three types of samples have been prepared for admittance measurements, differing in the way how the effective area is defined. The measurement geometry is either defined by cutting, by etching the ITO layer outside the active area, or by etching the ITO and the a-Si:H outside the active area. Admittance measurements reveal that the lateral conductivity of the ITO is high enough up to a frequency of to ensure a lateral equipotential surface. A simple equivalent network consisting of a parallel resistor-capacitor branch in series to a second resistor controls the cut sample. For the sample with just ITO layer etching, the effects of a lateral channel due to the a-Si:H layer have to be included. The finite dimensions of the sample modify the low-pass character of the channel. The sample with ITO and a-Si:H layer etching delivers the best measurement conditions. In all three cases the dispersion allows the surface doping level of the substrate to be extracted from the CV characteristics measured at .