Ultra-thin GaAs single-junction solar cells integrated with an AlInP layer for reflective back scattering

This paper proposes and demonstrates the use of a textured and lattice-matched semiconductor layer coated with a Au reflector for reflective back scattering to enhance the efficiency of single-junction solar cells with ultra-thin absorbers. The device structure studied in this work consists of an In_0.49Ga_0.51P/GaAs/In_0.49Ga_0.51P double-heterostructure single-junction solar cell with a GaAs absorber of either 300 nm or 1000 nm thick, as well as a textured Al_0.52In_0.48P layer coated with a highly reflective Au film. The devices, areas ranging from 0.3×0.3 mm² to 1×1 mm², are flip-chip bonded onto Si carrier substrates, covered by a contact metal grid (with a 9.7% or 10.7% shadow area for the 300 nm and 1000 nm devices, respectively) and a MgF₂/ZnS anti-reflective coating. Both types of device designs demonstrate an open-circuit voltage of 1.00 V, short-circuit current densities of 24.5 and 26.1 mA/cm², and power conversion efficiencies of 19.1% and 20.6%, respectively; these measurements are carried out under 1 sun solar radiation (AM 1.5G, 0.1 W/cm²). It is reasonable to expect that the short-circuit current densities and conversion efficiencies of these devices could reach 26.6 mA/cm² and 28.6 mA/cm², and 20.7% and 22.6%, respectively, when a typical contact grid layout with 2% surface coverage is used. These short-circuit current densities are only 3.6 and 1.6 mA/cm² lower than the maximum theoretical value 30.2 mA/cm², respectively.