| 1. |
- Roedl, C., et al.
(författare)
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Wurtzite silicon as a potential absorber in photovoltaics : Tailoring the optical absorption by applying strain
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:4
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Tidskriftsartikel (refereegranskat)abstract
- We present ab initio calculations of the electronic structure and the optical properties of wurtzite Si (Si-IV). We find an indirect band gap of 0.95 eV (Gamma(5) -> M-1) and an optically forbidden direct gap of 1.63 eV (Gamma(5) -> Gamma(10)), which is due to a backfolding of the L-1 state of Si in the diamond structure (Si-I). Optical absorption spectra including excitonic and local-field effects are calculated. Further, the effects of hydrostatic pressure, uniaxial strain, and biaxial strain on the absorption properties are investigated. Biaxial tensile strains enhance the optical absorption of Si-IV in the spectral range which is relevant for photovoltaic applications. High biaxial tensile strains (>4%) even transform Si-IV into a direct semiconductor.
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| 2. |
- Olsson, Pär, et al.
(författare)
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Ferromagnetic Compounds for High Efficiency Photovoltaic Conversion : The Case of AlP:Cr
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:22, s. 227204-
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Tidskriftsartikel (refereegranskat)abstract
- The photovoltaic conversion efficiency in usual semiconductors is limited to 30% while thermodynamics sets an upper limit of above 70%. Here we show how efficiencies in the 50% range could be achieved using carefully chosen magnetic doping in wide gap semiconductors. To meet the requirement to obtain useful compounds we propose rules and a selection method based on ab initio calculations coupled with material efficiency predictions. As a result of an investigation over hundreds of compounds, AlP:Cr was found to be the most promising semiconductor.
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| 3. |
- Zhang, S. -T, et al.
(författare)
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Importance of atmospheric aerosol pollutants on the degradation of Al2O3 encapsulated Al-doped zinc oxide window layers in solar cells
- 2022
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 30:5, s. 552-566
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric aerosol pollutants are considered for the first time for the durability evaluation of non-metallic photovoltaic materials on the example of pristine and Al2O3-encapsulated Al-doped zinc oxide (AZO) window layers. The AZO samples were exposed to a varied temperature and humidity cycle, completed or not by a daily deposition of (NH4)2SO4 or NaCl aerosols, typical pollutants in rural and marine environments, respectively. The samples exposed with and without the pollutants were compared after 1 and 2 weeks of the test. Optical transmittance and conductivity significantly degraded only for the samples exposed with the pollutants. Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy evidenced localized dissolution of the AZO film and chemical modification of the Al2O3 encapsulation. The most severe degradation was caused by (NH4)2SO4, which was attributed to the high stability of soluble [Zn (NH3)42+] complexes. The Al2O3 encapsulation improved chemical and physical stability of AZO in the presence of (NH4)2SO4 but not in the presence of NaCl. The latter can be explained by pitting corrosion of Al2O3. Optical transmission curves are coherent with the AZO layer thinning in the presence of NaCl and very localized AZO dissolution (most likely grain boundary etching) in the presence of (NH4)2SO4. The enhanced degradation of encapsulated AZO in the presence of atmospheric aerosol pollutants suggests that they cannot be neglected in the evaluation of barrier protection capacities of novel encapsulates and, more generally, in the outdoor durability assessment of novel photovoltaic materials and devices.
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