Projections of GaAs solar-cell performance limits based ontwo-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     

Closure for a plane fin heat sink with scale-roughened surfaces for volume averaging theory (VAT) based modeling

The present paper describes an effort to obtain closure for a volume averaging theory (VAT) based model of a plane fin heat sink (PFHS) with scale-roughened surfaces by evaluating the closure terms for the model using computer fluid dynamics (CFD). Modeling a PFHS as porous media based on VAT, specific geometry can be accounted for in such a way that the details of the original structure can be replaced by their averaged counterparts and the VAT based governing equations can be efficiently solved for a wide range of parameters. To complete the VAT based model, proper closure is needed, which is related to a local friction factor and a heat transfer coefficient of a representative elementary volume (REV). The terms in the closure expressions are complex and sometimes relating experimental data to the closure terms is difficult. In this work we use CFD to obtain detailed solutions of flow and heat transfer through an element of the scale-roughened heat sink and use these results to evaluate the closure terms needed for a fast running VAT based code, which can then be used to solve the heat transfer characteristics of a higher level heat sink. The objective is to show how heat sinks can be modeled as a porous media based on volume averaging theory and how CFD can be used in place of a detailed, often formidable, experimental effort to obtain closure for a VAT based model.     

Influence of perimeter recombination on high-efficiency GaAs p/nheteroface solar cells

Perimeter recombination currents have been characterized for 0.5-cm-square and 2-cm-square p/n GaAs solar cells. Measurements show that perimeter recombination dominates the n=2 dark current component of these high-efficiency solar cells. The results also suggest that perimeter recombination will be substantial even in much-larger-area solar cells. Although little influence on open-circuit voltage is expected, perimeter recombination may adversely affect the cell's one-sun fill factor. Because of its importance to one-sun applications, recombination at the junction perimeter must be suppressed before GaAs solar cells approach their limiting conversion efficiencies