Projections of GaAs solar-cell performance limits based on two-dimensional numerical simulation

The development of a comprehensive, two-dimensional numerical model for AlGaAs/GaAs solar cells is described. The model was used to identify loss mechanisms in present-day high-efficiency GaAs cells and to make realistic projections of attainable cell efficiencies. Numerical simulations show that achievable efficiencies of conventional heteroface cells made on high-quality GaAs films exceed 30% under 500 suns (AM1.5 direct spectrum). Both p-n and n-p cells are adversely affected by bandgap narrowing in p⁺ GaAs. For n-p cells, the use of heterojunction back-surface fields is advantageous and results in an increase of about 1.5% in efficiency. When the Shockley-Read-Hall lifetime parameters are set to infinity, the efficiency increases by only another 0.7%, which demonstrates that bulk material quality is not the major limiting factor in present-day cells. These efficiency projections, which are based on detailed device simulation and realistic material parameters, are only a few percentage points below the thermodynamic limit for GaAs cells