Material quality and design optimization for high efficiency GaAs solar cells

A methodology is developed to determine minority carrier lifetime and recombination velocity in high-efficiency GaAs p/n heteroface solar cells. A combination of measurements and modeling is used to demonstrate that a base lifetime of 8 ns and a heteroface recombination velocity of 1.25*10⁵ cm/s are necessary to simulate the spectral response, cell data, and leakage current in a 21.2% efficient GaAs cell. Optimization of the p/n heteroface structure shows that AM1.5 one-sun efficiencies of approximately 25% are achievable from a thin base/buffer design with a base lifetime of only 15 ns and a well-passivated back surface. In addition, it is shown that the doping dependence of the Shockley-Read-Hall lifetime is an important consideration in GaAs device modeling, especially if a shallow level ( approximately E_t=0.2 eV) limits the bulk lifetime.