Extended Analysis of Capacitance–Voltage Curves for the Determination of Bulk Dopant Concentrations of Textured Silicon Solar Cells

Capacitance–Voltage (
$C$
–
$V$
) measurements are an established method for determining the bulk dopant concentration
$N_{\rm bulk}$
of semiconductor devices. The extraction of
$N_{\rm bulk}$
requires knowledge of the surface area of the space-charge region (SCR). For textured solar cells, this surface area is enlarged, depending on texture and bias voltage. The amount of enlargement is a priori unknown, and there is no simple way of measuring directly it. In this paper, models that were previously proposed in the literature are employed to describe the SCR area. Substantial deficiencies in these models are revealed by comparison with a 3-D numerical simulation of the SCR geometry used as a benchmark. This approach leads to the development of a new analytical model that can properly describe the bias-voltage dependence of the surface area enlargement.
$C$
–
$V$
measurements over a large bias-voltage range are performed on various solar cells with different textures and resistivities. The new analytical model is employed to correct the measurement data for the influence of surface area enlargement. Thus,
$N_{\rm bulk}$
can be extracted without explicit knowledge of the enlargement. Comparison with four-point probe measurements shows excellent agreement, demonstrating the power of the new method to enable the
$C$
–
$V$
technique for use in
$N_{\rm bulk}$
determination for textured solar cells.