Electronic Properties of Wide Bandgap Pentenary Chalcopyrite Alloys and Their Photovoltaic Devices

We have used electronic and optical techniques to characterize alloys of the Cu(ln,Ga)(S,Se)₂ material system. The alloys were prepared such that the bandgap of the resultant materials was near 1.5 eV. These materials are interesting as the absorber layer of thin-film solar cell devices, and were studied in a solar cell device configuration. Electronic characterization techniques included admittance spectroscopy and drive-level capacitance profiling (DLCP). Optical techniques included transient-photocapacitance and transient-photocurrent spectroscopies. From these measurements we were able to determine defect activation energies and profiles, Urbach energies, and information about deeper (optical) defect positions and widths. These data are used to suggest a model of a deep electron trap 200 meV to 300 meV below the conduction band that is filled optically and emptied thermally, and may affect solar cell device performance