Progress in large area organometallic vapor phase epitaxy for III–V multijunction photovoltaics

Multijunction solar cells are fabricated using organometallic vapor phase epitaxy (OMVPE) to deposit subcells of GaInP and GaInAs on 150 mm diameter Ge substrates. We review the general challenges of achieving solar cell epitaxial growth on 150 mm dia. Ge and discuss basic GaInP material characterization. Metamorphic GaInP/GaInAs/Ge C4MJ epitaxial layers are characterized by in-situ curvature measurements during growth. A 98.5% relaxation is measured by high resolution X-ray diffraction reciprocal space mapping, and a threading dislocation density of 1.3×105 cm−2 is measured by cathodoluminescence in active regions of the device. Test batches of 20 kWp of cells, 1.0 cm2 in aperture area, are grown and fabricated on 100 mm and 150 mm dia. Ge wafers and average 40.2% and 40.1% efficiency, respectively, under 50 W/cm2 AM1.D illuminated current–voltage (LIV) testing. Finally, we demonstrate very large area, >72 cm2, triple junction XTJ space devices, averaging 29.3% efficiency for 73 such devices under space LIV testing (0.1353 mW/cm2, 28 °C, AM0).

► We use OMVPE to deposit epitaxial layers for high efficiency triple junction (3J) GaInP/GaInAs/Ge solar cells on 150 mm dia. Ge wafers. ► Challenges of III–V epitaxial growth for these devices are reviewed. ► Metamorphic terrestrial concentrator photovoltaics reaching 40% efficiency are demonstrated. ► Epitaxial devices in excess of 72 cm2 in area for 30% efficient space 3J devices are shown.