Energetics of Both Minority and Majority Carrier Transitions through Deep Defects in Wide Bandgap Pentenary Cu(In,Ga)(Se,S)2 Thin Film Solar Cells

Abstract

AbstractWe report and electronic and optical characterization of three wide-bandgap alloys of the Cu(InxGa1-x)(SeyS1-y)2 pentenary material system. Devices were characterized using admittance spectroscopy as well as drive-level capacitance profiling. The devices showed activated defect behavior typical of thin-film solar cell devices. Optical characterizations were carried out with Transient Photocapacitance and Transient Photocurrent spectroscopies. These data showed broad exponential bandtails with large Urbach energies, indicative of a moderately high degree of compositional and/or structural disorder. The temperature dependence of the TPC spectra was examined in detail and we were able to observe the thermal emission of electrons from defects into the conduction band. The emission energy of these features corresponds well with the measured optical threshold and the known bandgap of the cells. Thus we infer an upper bound of about 50meV for the lattice relaxation energy following the optical transition into the defect.