Dominant Recombination Path In Low-Bandgap Kesterite Cztse(S) Solar Cells From Red Light Induced Metastability

Hetero-junction kesterite Cu2ZnSn(S,Se)(4) solar cells with low bandgap obtained from three different methods of fabrication were exposed to red light illumination, and the changes observed in their electronic properties due to this exposure were studied via open circuit voltage transients, admittance spectroscopy, capacitance voltage profiling techniques, and SCAPS simulation fits to experimental data. The results from the aforementioned techniques, in combination with temperature-dependent current voltage analysis, can be used to reveal the dominant Shockley-Read-Hall recombination path at open circuit voltage. We also derived analytical expressions for the activation energy of the saturation current density and the diode quality factor for the specific case of a solar cell device that has no type inversion at the absorber/buffer interface and is limited by interface recombination in the open circuit condition. It is found that the dominant recombination pathway for the low bandgap Cu2ZnSn(S,Se)(4) solar cells under consideration is located in the space charge region and not at the absorber/buffer interface.