Prepared for Solar Energy Research Institute, under sub-contract XL 3-03124-1


The goal of this project was to begin -developing accurate, and ultimately predictive, device models for III-V concentrator cells. The project consisted of extending a one-dimensional numerical device model previously developed at Purdue to III-V solar cells. We also began verifying the accuracy of the code by comparing computed and measured solar cell characteristics. Gallium arsenide was selected because it is the most mature III-V technology and because GaAs solar cells have demonstrated high conversion efficiency [l,2,3]. The present device model should be useful in optimizing GaAs solar cells and forms a foundation that can be extended to other III-V homo- and heterostructure solar cells. The numerical device model developed in this work solves Poisson’s equation simultaneously with the electron and hole continuity equations without making common assumptions such as low-level injection, piece-wise uniform doping, neglect of space-charge recombination, etc. Materials models for GaAs solar cells (e. g. intrinsic carrier concentration, carrier mobilities, lifetimes, optical absorption and reflection coefficients, etc.) were compiled, evaluated, and in some cases extended. These materials models were then implemented into the numerical device model. The device model was also extended to analyze optical absorption and reflection from bare and anti-reflection (AR) coated cells. To test the GaAs cell model, we compared its predictions to measured results for an N+P cell (the shallow homojunction cell reported by Fan and co-workers) and a P+N cell (fabricated by Borrego and co-workers). In general, good agreement between theory and experiment was obtained for both concentrated and unconcentrated conditions. Although detailed comparisons of the model’s predictions with measured results continue, the present model is a useful tool for GaAs cell design and optimization.

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