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This paper presents the design parameters for a triple junction InGaP/GaAs/Ge space solar cell with a simulated maximum efficiency of 36.28% using Silvaco ATLAS Virtual Wafer Fabrication tool. Design parameters include the layer material, doping concentration, and thicknesses. An initial dual junction InGaP/GaAs model of a known Japanese solar cell was constructed in Silvaco ATLAS to an accuracy of less than 2% with known experimental Voc and Jsc performance results, validating the use of computer modeling to accurately predict solar cell performance. Once confidence of the model's meshing, material property statements, model statements, light file, and numerical methods were established, only the layer doping concentration levels and thicknesses were modified in order to improve the cell's power out efficiency. Simulations of the dual junction cell began by first changing only the doping concentrations and thicknesses to the values obtained from previous work using a genetic algorithm which showed a 0.6% increase in efficiency. Further improvements to the genetic algorithm design parameters showed an overall increase of 0.83% efficiency. Next, a triple junction InGaP/GaAs/Ge cell was modeled by adding a Ge layer to the validated dual junction InGaP/GaAs model. (The triple junction model could not be validated due to lack of published experimental data.) Applying the same process showed increased power output for the triple junction cell. The additional improvement to the genetic algorithm design parameters was principally based on the knowledge that the top InGaP layer is the current limiting layer. Hence, the top layer thickness was maximized until middle and bottom layer shadowing effects began to decrease power output. Over 250 simulations were performed and recorded. Maximum doping concentrations used real world limitations of 5e19 cm-3 for InGaP and GaAs and 3e18 cm-3 for Ge for all simulations. This process produc- ed the design parameters for a 36.28% efficient triple junction solar cell. A provisional patent has been filed for this design.
Date of Conference: 7-12 June 2009