Modelling of lattice matched dilute nitride 4-junction concentrator solar cells on Ge substrates

Ochoa, Mario; García, Iván; Lombardero, Iván; Rey‐Stolle, Ignacio; Algora, Carlos; Johnson, Andrew; Davies, J. I.; Tan, Kang Hai; Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt; Ochoa-Martínez, Efraín; Gabás, M.

doi:10.1063/1.4962101

Cited by 10 publications

(17 citation statements)

References 11 publications

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“…The top GaInP and Ga(In)As subcells exhibit EQE and IQE similar to obtained when growing them in GaInP/Ga(In)As/Ge 3J solar cells developed in our lab . The GaNAsSb subcell exhibits a low EQE due to the low material quality obtained combined with a thin absorber layer, as commented previously . The IQE values obtained for this subcell are around 0.6 and below.…”

Section: Performance Of the 4j Solar Cellsupporting

confidence: 67%

“…The absorber thickness used is just 1000 nm, which is lower than needed for a complete optical absorption. This thickness was used because it allowed achieving the highest quantum efficiency: given the low carrier diffusion length in this material, thicker absorber layers did not give rise to higher quantum efficiencies . Finally, the sample is transferred back to the MOVPE reactor for growing the middle tunnel junction and the top GaInP/Ga(In)As tandem structure.…”

Section: Movpe + Mbe 4j Solar Cellmentioning

confidence: 99%

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Degradation of subcells and tunnel junctions during growth of GaInP/Ga(In)As/GaNAsSb/Ge 4‐junction solar cells

García

Ochoa

Lombardero

et al. 2017

Progress in Photovoltaics

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A GaInP/Ga(In)As/GaNAsSb/Ge 4J solar cell grown using the combined MOVPE + MBE method is presented. This structure is used as a test bench to assess the effects caused by the integration of subcells and tunnel junctions into the full 4J structure. A significant degradation of the Ge bottom subcell emitter is observed during the growth of the GaNAsSb subcell, with a drop in the carrier collection efficiency at the high energy photon range that causes a~15% lower J sc and a V oc drop of~50 mV at 1-sun. The V oc of the GaNAsSb subcell is shown to drop by as much as~140 mV at 1-sun. No degradation in performance is observed in the tunnel junctions, and no further degradation is neither observed for the Ge subcell during the growth of the GaInP/Ga(In)As subcells. The hindered efficiency potential in this lattice-matched 4J architecture due to the degradation of the Ge and GaNAsSb subcells is discussed. At this stage of development, it is pertinent to have a closer look at the integration of components forming the 4J structure. For example, the insertion of the dilute nitride subcell in the 3J structure brings about added thermal loads to the Ge bottom subcell, an effect accentuated by the fact that dilute nitrides usually require an annealing step to improve their electronic properties. The dilute-nitride subcell itself suffers annealing during the growth of the upper subcells, which could be expected to have an impact on its performance. The focus has to be put in identifying and quantifying these effects, and redesigning the growth process to minimize their impact.In this work, we present a detailed characterization of our 4J solar cell, based on a prototype structure achieved by a combination of MOVPE + MBE growth methods, and using a GaNAsSb junction.This solar cell succeeds in integrating 4 component junctions into a monolithic, lattice matched structure, but it is still far from being a high efficiency device, mainly due to sub-optimum characteristics of the dilute nitride subcell. However, the device provides valuable insight into the integration of the dilute nitride subcell into a 4J solar cell. We focus mainly on the effect of thermal load on the performance of the Ge and GaNAsSb bottom subcells, and the tunnel junctions. It is found that significant losses are at stake, mainly in the Ge and GaNAsSb subcells, which can limit the potential of this 4J solar cell structure to compete in efficiency with other architectures.

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Section: Performance Of the 4j Solar Cellsupporting

confidence: 67%

Section: Movpe + Mbe 4j Solar Cellmentioning

confidence: 99%

Degradation of subcells and tunnel junctions during growth of GaInP/Ga(In)As/GaNAsSb/Ge 4‐junction solar cells

García

Ochoa

Lombardero

et al. 2017

Progress in Photovoltaics

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“…The growth process comprises a sequence of MOVPE (GaInP nucleation on Ge and tunnel junction) + MBE (GaNAsSb subcell) + MOVPE (GaInP/Ga(In)As top junctions, including tunnel junctions). Given the low minority carrier diffusion length in the dilute nitride material, the GaNAsSb subcell absorber was made as thin as 1 \xm [4], [5]. These structures were processed into solar cell devices using gold-based metal and standard photolithography techniques.…”

Section: Movpe+mbe 4 J Solar Cellmentioning

confidence: 99%

“…Light I-V curves were measured on these 4J solar cells. We have published previous work about the performance and particularities in the shape of the I-V curve of the 4J, predicted using simulations with inputs from the characterization results of GaNAsSb 1J and GaNAsSb/Ge 2J cells [4], [5]. As for this work, we are mostly interested in the open circuit voltage (V oc ), which we showed to be around 420 mV for the GaNAsSb solar cell as an independent device [4].…”

Section: B Open Circuit Voltage (V Oc )mentioning

confidence: 99%

Component Integration Effects in 4-Junction Solar Cells with Dilute Nitride 1eV Subcell

García

Ochoa

Lombardero

et al. 2017

2017 IEEE 44th Photovoltaic Specialist Conference (PVSC)

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A GaInP/Ga(In)As/GaNAsSb/Ge 4-junction solar cell grown using combined MOVPE+MBE growth is used to analyze the effects during the integration of the subcell components into the full 4J structure. In this preliminary study, the Ge subcell is observed to suffer about 15% Jsc drop and ~50 mV Voc loss at 1-sun, while the Voc of the GaNAsSb subcell drops by as much as ~ 140 mV. The degradation of the Ge and GaNAsSb subcells in the current-matched 4J structure can hinder its efficiency potential to a higher extent than in the GaInP/Ga(In)As/Ge 3J. Besides, high quality GaNAsSb and Ge subcells would still limit the current and require redesigning the top subcells to achieve optimum efficiencies.

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“…Using this technique, high‐performance triple‐junction cells with 44% conversion efficiency under concentrated sunlight as well as 31% conversion efficiency for one‐sun space illumination have been demonstrated. On the other hand, only little progress for the development of 4J dilute nitride solar cells has been reported, with initial demonstrations employing Ge as bottom junction and only one dilute nitride subcell …”

Section: Introductionmentioning

confidence: 99%

Lattice‐matched four‐junction tandem solar cell including two dilute nitride bottom junctions

Aho

Isoaho

Hytönen

et al. 2018

Progress in Photovoltaics

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Monolithic four-junction solar cells incorporating two dilute nitride (GaInNAsSb) bottom junctions are reported. The dilute nitride junctions have band gaps of 0.9 and 1.2 eV, while the top junctions have band gaps of 1.4 and 1.9 eV. By using experimental-based parametrization, it was estimated that the four-junction solar cell could theoretically exhibit efficiency levels of 34.7% at one sun, 43.2% at 100 suns, and 46.4% at 1000 suns for AM1.5D illumination. The most challenging subcell in terms of fabrication is the GaInNAsSb bottom junction with 0.9 eV band gap. For this subcell, a background doping level down to 5 × 10 14 cm −3 and a high charge carrier lifetime up to 2 to 4 nanoseconds are reported, which reflects high values for current and voltage. An experimental AlGaAs/GaAs/GaInNAsSb/GaInNAsSb solar cell structure was fabricated by molecular beam epitaxy. At one-sun AM1.5D illumination, the experimental cell exhibited an efficiency of 25%, an average quantum efficiency of 91%, and an open circuit voltage, which is about 87% of the estimated potential.The cell exhibited maximum efficiency of 37% at 100-sun concentration.

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Modelling of lattice matched dilute nitride 4-junction concentrator solar cells on Ge substrates

Cited by 10 publications

References 11 publications

Degradation of subcells and tunnel junctions during growth of GaInP/Ga(In)As/GaNAsSb/Ge 4‐junction solar cells

Degradation of subcells and tunnel junctions during growth of GaInP/Ga(In)As/GaNAsSb/Ge 4‐junction solar cells

Component Integration Effects in 4-Junction Solar Cells with Dilute Nitride 1eV Subcell

Lattice‐matched four‐junction tandem solar cell including two dilute nitride bottom junctions

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