Degradation of solar cell performance by areal inhomogeneity

Calculations have been made that show how severely areal inhomogeneity can degrade solar-cell conversion efficiency. Two general types of areal inhomogeneity are discussed. In the first type, the emitter recombination current controls the I- V characteristics for voltages near the maximum power voltage, and areal variations in the structural or material parameters of the emitter are assumed to occur. For this type of areal inhomogeneity, the base recombination current controls the dark I- V characteristics, and areal variations in the base minority-carrier lifetime are assumed to occur. For this type, the poor-quality area again dominates in determining the conversion efficiency, though less strongly than for the first type of areal inhomogeneity. An extension of the method used to demonstrate this behavior can provide a first-order solution of the general three-dimensional boundary-value problem resulting from areal inhomogeneity; this extension is briefly described.