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Building on previous simulation results, this work examines experimentally the incorporation of a longpass (LP) distributed Bragg reflector (DBR), as compared to a standard matched pair DBR, between the GaAs and InGaAs subcells of a triple junction inverted metamorphic design. The GaAs cell was not optically thick, to improve radiation tolerance, and contained InGaAs quantum wells, to increase subcell current generation. Both DBR structures improved bulk GaAs subcell collection in the physically thin absorber, however the LPDBR significantly reduced optical loss in the bottom junction caused by parasitic low energy reflections present in the standard DBR. This shifted the current limiting junction from the bottom InGaAs junction in the case of the DBR to the top InGaP junction, as designed. Simulation and experimental results of external quantum efficiency are presented and discussed.

MicroLink Devices has deposited screen printed silver contacts on bulk pseudomorphic InGaAs and for the first time on epitaxial thin film foils. MicroLink has achieved contact resistances of 1E-6 Ohms·cm−2 on bulk InGaAs, and 4E-2 Ohms·cm−2 on solar cell foils. Ink formulations with tin are also explored. This work shows an alternative, low-cost, and high-throughput method for contacting III-V solar cells.

The authors report on the metal-organic vapor phase epitaxial (MOVPE) growth of all III-phosphide (AlInPInGaP) Distributed Bragg Reflectors (DBRs) on large GaAs substrates and their application for multijunction (MJ) solar cell device. DBRs with peak reflectance of 890 nm at GaAs bandgap energy were grown on top of inverted GaAs single junctions. All phosphide DBRs are compatible with epitaxial lift off processing of solar cells. The DBRs grown on 150 mm (6") substrates exhibited smooth surfaces and high degree of homogeneity. In the preliminary integration tests, the dual junction InGaP/GaAs solar cells with AlInP-GaInP DBR resulted in an increase of 3% in J sc and 44% increase in the integrated EL intensity of both GaAs and InGaP peaks when testing under high injection currents. The V oc and FF did not change with the DBR integration into the 2J cells.

MicroLink Devices has deposited Ag contacts via screen printing on n-GaAs epilayers on 150 mm GaAs wafers. We print either directly on n-GaAs or on an electron-beam evaporated seed layer. After annealing and self-aligned etch back, we achieve printed spaces of ~70 $\mu$m, contact resistances of

MicroLink Devices has developed two-terminal monolithic three-junction (3J) GaInP/GaAs/GaInAs epitaxial liftoff (ELO) solar cells with certified 37.75 ± 0.53% AM1.5G 1-Sun power conversion efficiency at 25°C. Additionally, MicroLink is developing two-terminal monolithic four-junction (4J) ELO solar cells based on GaInP/GaAs/GaInAs/GaInAs subcells with a peak preliminary AM0 1-Sun efficiency of 34.31%. All of these ELO solar cells were manufactured entirely with production tools and processes on reusable 150 mm diameter GaAs substrates.

Back-contact solar cells potentially achieve higher efficiency by moving all the electrical connections to the rear of the cell, thus eliminating shadow losses as well as enabling new array assembly approaches. In spite of the many advantages of this technology, as demonstrated in commercial manufacturing of silicon cells, the process complexity to create through wafer vias has limited its use in III-V solar cells. We present a simple, three-mask process flow for fabricating through-epitaxial via (TEV) back-contact multi-junction epitaxial liftoff (ELO) solar cells in this paper. Electrical characterization showed 3J cells with 25.9% efficiency (1 sun AM1.5 spectrum) without AR coating and similar performance to standard top-contact devices.