42percent 500X Bi-Facial Growth Concentrator Cells

摘要

Data are presented from three-junction concentrator photovoltaic cells using a new cell architecture (1.9eV InGaP top cell lattice-matched to a 1.42eV GaAs middle cells on one side of a infrared-transparent GaAs wafer with a lattice-mismatched 0.95eV InGaAs bottom cell grown isolated on the wafer backside). The cell uses a new epitaxial bifacial growth (BFG) technique. The impetus is to replace the 0.67eV Ge bottom cell in the standard three junction InGaP/GaAs/Ge tandems with a higher bandgap 0.95eV InGaAs cell that boosts the bottom cell voltage by about 40percent while maintaining a simple high-yield cell process without use of complex large area epitaxial liftoff or wafer bonding steps used to make similar cell stacks. Efficiency was independently-verified by NREL for a 1cm X 1cm cell (42.3percent at 406 suns, with Voc 3.452V, 87.1percent FF and 1 X Jsc of 14.07mA/cm~(2), at 25 deg C AM1.5D, 100mW/cm~(2)), which was the world record at the time of the CPV-7 conference. No degradation was seen during concentrated solar operation after a 2000hr 165C burn-in and PbSn solder tests. Average efficiency of 1cm~(2) cells designed for 500 suns at 1018 suns was 40.5percent (Spire test, 25 deg C, spectrally corrected flash simulator). Measured efficiency temperature coefficient for gen2 cells is - 0.06percent/(deg C), similar to InGaP/GaAs/Ge tandems.