Impact of transparent conductive oxide on the admittance of thin film solar cells

The impact of transparent electrically conducting oxide (TCO) on the admittance measurements of thin film p-i-n a-Si:H solar cells was investigated. Admittance measurements on solar cell devices, with different area and geometry, in a wide range of frequencies and biases were performed. The admittance measurements of the investigated solar cells, which use the TCO as an electrical contact, showed that the high frequency admittance per area unit depends on the area. This effect increases both with the probe frequency and the size of the solar cells. Transmission line model valid for strip geometry which explains how the resistivity of the TCO layer impacts the measured admittance of the p-i-n diode was presented. An estimate of the critical length of the strip solar cell over which the measured diode capacitance is affected by the TCO is given. The transmission line model allows to estimate also the lumped parasitic series resistance Rs of solar cells with strip geometry.