InGaP/GaAs/InGaAs 41% concentrator cells using bi-facial epigrowth

Spire Semiconductor has demonstrated a new bi-facial epigrowth manufacturing process for InGaP/GaAs/InGaAs N/P tandem concentrator cells. NREL has verified 1cm² cells as 41.0% efficient at 500X, and 5.5mm cells as 41.4% at 334X, AM1.5D, 25C, matching within measurement error the world record efficiency. A lattice-mismatched 0.94eV InGaAs cell is epitaxially grown on the backside of a lightly doped, N-type GaAs wafer, the epiwafer is flipped in the MOCVD reactor glove box, and 1.42eV GaAs and 1.89eV InGaP cells are grown lattice matched on the opposite wafer surface. Cells are then made using only standard III-V process steps. The bi-facial process is an alternative to the inverted metamorphic (IMM) process. It does not use epitaxial liftoff and wafer bonding as in the IMM approach but does require breaking the growth into two parts and flipping the epiwafer, which we believe is an easier task.