Efficiency Enhancement of Single-Junction GaAs Solar Cells with Gradually Doped p-n Junction Active Layers

Gradually doped p-n junction structures are investigated in this study to improve the power conversion efficiency of GaAs single-junction solar cells. We investigated the impact on enhancing the efficiency of GaAs solar cells with four different p-n junction doping profiles by comparing computer simulation results and fabricated device characteristics. GaAs solar cells with various graded doping profiles are epitaxially grown on p-type GaAs (100) substrates with 6' tilt angles toward [111] using metalorganic vapor phase epitaxy (MOVPE). GaAs solar cells with four different doping profiles are prepared: sample A: uniformly doped emitter and base layers; sample B: gradually doped emitter and uniformly doped base layers; sample C: uniformly doped emitter and gradually doped base layers; and sample D: gradually doped emitter and base layers. The GaAs solar cells are fabricated using standard photolithography, metal deposition, rapid thermal annealing, wet-chemical etching processes, and chip isolation. Photovoltaic device parameters of the GaAs cells are characterized under AM1.5 global illumination. It is found that a graded doping profile in the base layer plays an important role in improving the efficiency of GaAs solar cells.