Space-charge-limited current in CuxS/CdS solar cells
A space-charge-limited current model has been used to consistently and quantitatively model the gross electrical properties of Cu in xS/CdS heterojunctions not explained by standard p-n junction theory. Quantitative fits were ob tained for the dark and light crossover of the I–V curves, the evolution of I–V from near Ohmic to rectifying during heat treatment, the high forward voltage drop in the dark, the non-exponential dependence of I on V, and the temperature independent slope of the I–V curves. These were found for CdS trap densities in the 1013} to 1015} cm−3 range, polycrystalline CdS mobilities in the 1 to 10 cm2} /V-seC8} range, and conduction electron concentrations in the 10 to 1010} cm−3 10 cm range in the thin Cu compensated region of CdS produced during cell fabrication heat treatments as monitored by zero bias capacitance. These results imply that entirely different physical mechanisms than those used to describe standard p-n junctions control the dark and light I–V characteristics and the conversion efficiency of these solar cells.