Quadruple-Junction Inverted Metamorphic Concentrator Devices

Abstract

Abstract-We present results for quadruple-junction inverted metamorphic (4J-IMM) devices under the concentrated direct spectrum and analyze the present limitations to performance. The devices integrate lattice-matched subcells with rear heterojunctions, as well as lattice-mismatched subcells with low threading dislocation density. To interconnect the subcells, thermally stable lattice-matched tunnel junctions are used, as well as a metamorphic GaAsSb/GalnAs tunnel junction between the lattice-mismatched subcells. A broadband antireflection coating is used, as well as a front metal grid designed for high concentration operation. The best device has a peak efficiency of (43.8 ± 2.2)% at 327-sun concentration, as measured with a spectrally adjustable flash simulator, and maintains an efficiency of (42.9 ± 2.1)% at 869 suns, which is the highest concentration measured. The V oc increases from 3.445 V at 1-sun to 4.10 V at 327-sun concentration, which indicates high material quality in all of the subcells. The subcell voltages are analyzed using optical modeling, and the present device limitations and pathways to improvement are discussed. Although further improvements are possible, the 4 J-IMM structure is clearly capable of very high efficiency at concentration, despite the complications arising from utilizing lattice-mismatched subcells.

Optimization of Multijunction Solar Cells Through Indoor Energy Yield Measurements

“…The 4J cells used are IMM devices with two metamorphic 1-and 0.7-eV GalnAs subcells [15]. The useful wavelength range for this cell is ~300 to ^1850 nm.…”

“…The useful wavelength range for this cell is ~300 to ^1850 nm. These devices exhibit strong luminescence, even in the metamorphic junctions, as shown in [15]. The P max maps for these devices were taken by automatically sweeping the concentration in each junction from 0 to 1.2 suns (referenced to the AMI.5 G173-direct spectrum at 1000 W/m 2 ) in six steps, which gives a total of 6 4 = 1296 I-V curve measurements.…”

Temperature-Induced Degradation of Thin-Film III–V Solar Cells for Space Applications

“…N OVEL III-V solar cell preparation approaches such as inverted metamorphic (IMM) growth [1]- [3], waferbonding [4] and mechanical stacking [5] require at least one growth substrate removal to create an operational device. Techniques such as epitaxial lift-off (ELO) [6]- [9] and controlled spalling [10], [11] allow for substrate removal without destruction of the expensive growth substrate, thus allowing for substrate re-use [12], [13].…”

“…The released active cell structures have the intrinsic potential to be turned into genuine thin-film devices if they are transferred to a thin and flexible carrier. Such thin-film III-V devices offer excellent characteristics for implementation in next generation space solar panels, as they allow for a significant weight reduction on panel level [14], while at the same time offering the highest possible solar cell efficiencies [3], [15], [16]. Space, however, also provides a harsh environment (vacuum, harsh UV, electron and proton radiation, temperature cycling) which adds additional design challenges.…”

Design flexibility of ultra-high efficiency 4-junction inverted metamorphic solar cells

“…The 4-junction inverted metamorphic (4J-IMM) solar cell has been shown to be capable of achieving extremely high efficiency despite the use of lattice-mismatched subcells [1]. Lattice-matched high-bandgap GalnP and GaAs subcells are grown first on a GaAs substate.…”