42.3% Efficient InGaP/GaAs/InGaAs concentrators using bifacial epigrowth

Spire Semiconductor has demonstrated a new bi-facial epigrowth manufacturing process for InGaP/GaAs/InGaAs N/P tandem concentrator cells. A lattice-mismatched 0.94 eV InGaAs cell is epitaxially grown on the backside of a lightly doped, N-type GaAs wafer, the epiwafer is flipped, rinsed, and 1.42 eV GaAs and 1.89 eV InGaP cells are grown lattice matched on the opposite wafer surface. Cells are then made using only standard III-V process steps. NREL verified that 1 cm cells achieve 42.3% efficiency at 406 suns, AM1.5D, 25°C. This establishes a new world record, exceeding the previous record efficiency of 41.6% set by an InGaP/InGaAs/Ge cell. The bi-facial tandems exhibit superior performance relative to Ge based triple junction cells due to improved current matching. In addition they are simpler to fabricate than the inverted metamorphic (IMM) process because epitaxial liftoff and wafer bonding are not required.