Space-charge-limited-current diode model for CuxS/CdS solar cells and their degradation

A space-charge-limited-current diode model for CuxS/CdS solar cells accurately models their current-density-versus-voltage (J-V) curves for a 9.2% efficient device and a 4.1% efficient device that degraded to 0.3% efficiency in hot-moist air. For a 1-μm-thick, high-resistance region of Cu compensated CdS at the interface to the CuxS, all the measured fill factors from 0.54 to 0.71 and the open-circuit voltages from 0.41 to 0.52 V are well fit for steady-state conduction electron concentrations between 1.2×109 and 6.9×1010 cm−3 and for electron trap densities between 7×1014 and 5×1018 cm−3 eV−1 at energies of 0.3–0.5 eV below the conduction-band edge of this high-resistance CdS region. The trap changes that occur with short-circuit current degradation increase the fill factor. A CuxS/CdS configuration is proposed to reduce reproducibility problems and to eliminate all the known modes of degradation with the possible exception of photoinduced degradation. Efficiency increases of 10%–11% are projected.