Point Contact Admittance Spectroscopy of Thin Film Solar Cells

Abstract

ABSTRACTWe present the new characterization technique of multi-dimensional admittance measurements. In standard admittance measurements, a semiconductor device is probed in the transverse dimension, between flat plate contacts. We extend such measurements to distributed, possibly non-uniform solar cells where one of the two contacts has very small (point-like) dimensions. As a result, both the real and displacement currents spread into lateral directions while flowing between the electrodes. Correspondingly, the probing electric field may result in contact voltages that are laterally not equipotential. The spatial voltage distribution will depend on the probing DC bias and AC frequency. The resulting measurement will give information about the system’s lump parameters, such as open circuit voltage, sheet and shunt resistances, as well as the presence and location of shunts. Understanding of the measurement is developed through intuitive and analytic models. Numerical models, utilizing finite element circuits, are used to verify the analytic results, and also may be directly compared to or used to fit experimental data. While our focus is on introducing the physical theory, early experimental results demonstrating spatial scaling are shown.