Article

Photovoltaic properties of low-bandgap (0.7–0.9 eV) lattice-matched GaInNAsSb solar junctions grown by molecular beam epitaxy on GaAs

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Abstract

We demonstrate single junction GaInNAsSb solar cells with high nitrogen content, i.e. in the range of 5–8%, and bandgap energies close to 0.7 eV grown by molecular beam epitaxy. A good crystalline quality is demonstrated for the entire range of N concentrations. An average external quantum efficiency of 0.45 is demonstrated for GaInNAsSb solar cell with 6.2% N exhibiting a bandgap of 0.78 eV (no antireflection coatings has been applied). The internal quantum efficiency for the cell is 0.65 at E g + 0.2 eV. The solar cells exhibited bandgap-voltage offsets between 0.55 V (for N = 5.3%) and 0.66 V (for N = 7.9%). When used in a six-junction solar cell architecture under AM1.5D illumination, the estimated short-circuit current density corresponding to the 0.78 eV cell is 8.2 mA/cm ² . Furthermore, using the parameters obtained for the GaInNAsSb junction with 6.2% N, we have estimated that such six-junction solar cell architecture could realistically attain an efficiency of over 50% at 1000 suns concentration.

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... Detailed description for the MBE processes related to GaInNAsSb fabrication are given elsewhere. [9][10][11] The current-voltage (IV) characteristics of all cells were measured at 1 sun. In addition, the LM 4J solar cell was measured with concentration up to 1000 suns. ...
... In high-performance multijunction solar cells, the bandgap of the GaInNAsSb junction has been typically limited to energies higher than 0.9 eV. Recently, we have demonstrated that high-performance narrow-bandgap (<0.8 eV) junctions can have good current generation 10 and have potential to be usable as bottom junctions for 5J and 6J architectures. For the dilute nitride solar cells, the series resistance is clearly not an issue, but maintaining high charge carrier lifetimes and low background doping levels is even more critical for high (>6%) N content. ...
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... There has been great interest in dilute nitride III-V-N materials during the last two decades, driven in part by their potential application in multijunction solar cells (Friedman et al., 1998;Geisz et al., 2018;Harris, 2005;Isoaho et al., 2019;Johnston et al., 2005;Kim et al., 2014c;Kosa et al., 2016;Kurtz et al., 2002;Miyashita et al., 2013Miyashita et al., , 2012Ptak et al., 2005Ptak et al., , 2009Sukeerthi et al., 2018) which are expected to outperform single-junction devices. Conversion efficiency of 46.1% has been reported for four-junction solar cells under concentrated light, using wafer bonding to combine 2 two-junction solar cells grown on InP and GaAs substrates (Dimroth et al., 2016). ...
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... Such GaInP/GaAs/GaInNAsSb solar cells had an efficiency of 44.0% under concentration, lower than the theoretical limit, since epitaxial growth and material quality problems inherent to quaternary and quinary dilute nitride alloys severely affect carrier dynamics [11]. Despite the intense activity of many groups and some relevant advances [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] no improvements in conversion efficiency with three or four-junction cells have been certified since 2016 [1]. ...
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Conference Paper
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