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Degradation of Ge subcells by thermal load during the growth of multijunction solar cells

Barrigón, Enrique LU ; Ochoa, Mario; García, Ivan; Barrutia, Laura; Algora, Carlos and Rey-Stolle, Ignacio (2018) In Progress in Photovoltaics: Research and Applications 26(2). p.102-111
Abstract

Germanium solar cells are used as bottom subcells in many multijunction solar cell designs. The question remains whether the thermal load originated by the growth of the upper layers of the multijunction solar cell structure affects the Ge subcell performance. Here, we report and analyze the performance degradation of the Ge subcell due to such thermal load in lattice-matched GaInP/Ga(In)As/Ge triple-junction solar cells. Specifically, we have detected a quantum efficiency loss in the wavelength region corresponding to the emitter layer (which accounts for up to 20% loss in equivalent JSC) and up to 55 mV loss in VOC of the Ge subcell as compared with analogous devices grown as single-junction Ge solar cells on the... (More)

Germanium solar cells are used as bottom subcells in many multijunction solar cell designs. The question remains whether the thermal load originated by the growth of the upper layers of the multijunction solar cell structure affects the Ge subcell performance. Here, we report and analyze the performance degradation of the Ge subcell due to such thermal load in lattice-matched GaInP/Ga(In)As/Ge triple-junction solar cells. Specifically, we have detected a quantum efficiency loss in the wavelength region corresponding to the emitter layer (which accounts for up to 20% loss in equivalent JSC) and up to 55 mV loss in VOC of the Ge subcell as compared with analogous devices grown as single-junction Ge solar cells on the same type of substrates. We prove experimentally that there is no direct correlation between the loss in VOC and the doping level of the base. Our simulations show that both the JSC and VOC losses are consistent with a degradation of the minority carrier properties at the emitter, in particular at the initial nanometers of the emitter next to the emitter/window heterointerface. In addition, we also rule out the gradual emitter profile shape as the origin of the degradation observed. Our findings underscore the potential to obtain higher efficiencies in Ge-based multijunction solar cells if strategies to mitigate the impact of the thermal load are taken into consideration.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Ge solar cells, multijunction solar cells, thermal degradation, thermal load, EU Horizon 2020, NEXTNANOCELLS, Grant 656208
in
Progress in Photovoltaics: Research and Applications
volume
26
issue
2
pages
10 pages
publisher
John Wiley & Sons
external identifiers
  • scopus:85040729825
ISSN
1062-7995
DOI
10.1002/pip.2948
language
English
LU publication?
yes
id
1d472438-713f-4f80-b067-84ee76ab1d91
date added to LUP
2018-01-30 07:50:24
date last changed
2018-05-16 14:10:16
@article{1d472438-713f-4f80-b067-84ee76ab1d91,
  abstract     = {<p>Germanium solar cells are used as bottom subcells in many multijunction solar cell designs. The question remains whether the thermal load originated by the growth of the upper layers of the multijunction solar cell structure affects the Ge subcell performance. Here, we report and analyze the performance degradation of the Ge subcell due to such thermal load in lattice-matched GaInP/Ga(In)As/Ge triple-junction solar cells. Specifically, we have detected a quantum efficiency loss in the wavelength region corresponding to the emitter layer (which accounts for up to 20% loss in equivalent J<sub>SC</sub>) and up to 55 mV loss in V<sub>OC</sub> of the Ge subcell as compared with analogous devices grown as single-junction Ge solar cells on the same type of substrates. We prove experimentally that there is no direct correlation between the loss in V<sub>OC</sub> and the doping level of the base. Our simulations show that both the J<sub>SC</sub> and V<sub>OC</sub> losses are consistent with a degradation of the minority carrier properties at the emitter, in particular at the initial nanometers of the emitter next to the emitter/window heterointerface. In addition, we also rule out the gradual emitter profile shape as the origin of the degradation observed. Our findings underscore the potential to obtain higher efficiencies in Ge-based multijunction solar cells if strategies to mitigate the impact of the thermal load are taken into consideration.</p>},
  author       = {Barrigón, Enrique and Ochoa, Mario and García, Ivan and Barrutia, Laura and Algora, Carlos and Rey-Stolle, Ignacio},
  issn         = {1062-7995},
  keyword      = {Ge solar cells,multijunction solar cells,thermal degradation,thermal load,EU Horizon 2020,NEXTNANOCELLS,Grant 656208 },
  language     = {eng},
  month        = {02},
  number       = {2},
  pages        = {102--111},
  publisher    = {John Wiley & Sons},
  series       = {Progress in Photovoltaics: Research and Applications},
  title        = {Degradation of Ge subcells by thermal load during the growth of multijunction solar cells},
  url          = {http://dx.doi.org/10.1002/pip.2948},
  volume       = {26},
  year         = {2018},
}