Temperature dependence of equivalent circuit parameters used to analyze admittance spectroscopy and application to CZTSe devices

We present a device physics and equivalent circuit model for admittance spectroscopy of CZTSe based photovoltaic devices. The experimental variations of the capacitance and conductance in the depletion width are reproduced for state of the art coevaporated CZTSe devices. We will show that simple Arrhenius analysis of the main capacitance step seen in CZTSe results in erroneous values for the dominant acceptor energy. We will also show that the bulk resistivity in the quasi-neutral region (QNR), even in the presence of the dominant acceptor freezeout, cannot account for the observed increase in series resistance which is responsible for the temperature dependent frequency shift of the capacitance step. Thus, we suggest that dopant freezeout must affect another component of the lumped series resistance such as a non-Ohmic back contact.