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Chalcogénures : Photovoltaïque et 2D
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The Determination of the Optical Bandgap of the Bernal and Rhombohedral Boron Nitride Polymorphs 
Auteur(s): Rousseau A., Moret M., Valvin P., Desrat W., Li Jiahan, Xue Lianjie, Janzen E., Edgar James, Cassabois G., Gil B.
(Article) Publié:
Physical Review Materials, vol. 5 p.064602 (2021)
Ref HAL: hal-03263151_v1
DOI: 10.1103/PhysRevMaterials.5.064602
WoS: 000663317400002
Exporter : BibTex | endNote
11 Citations
Résumé: We report a study of polymorphic boron nitride samples. We interpret the photoluminescence line at 6.032±0.005 eV, that can be recorded at 8K in sp2-bonded boron nitride, as being the signature of the excitonic fundamental bandgap of the Bernal (or graphitic) boron nitride polymorph (bBN). This is determined by advanced photoluminescence measurements combined with x-ray characterizations on pure hexagonal boron nitride (hBN) and on polymorphic crystal samples, later compared with the theoretical predictions of Lorenzo Sponza, et al., Physical Review B 98, 125206 (2018). The overall picture is consistent with a direct excitonic fundamental bandgap of the Bernal (or graphitic) polymorph of boron nitride. This value dXb = 6.032±0.005 eV is higher than the indirect bandgap of hBN (iXh =5.955±0.005 eV).
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Analysis of the gallium gradient in Cu(In1-xGax)Se-2 absorbers by X-ray diffraction
Auteur(s): Iatosti C., Moret M., Tiberj A., Briot O.
(Article) Publié:
Solar Energy Materials And Solar Cells, vol. 220 p.110847 (2021)
Texte intégral en Openaccess : 
Ref HAL: hal-03175976_v1
DOI: 10.1016/j.solmat.2020.110847
WoS: WOS:000596261300007
Exporter : BibTex | endNote
Résumé: In order to analyze why the CIGS (CuInGaSe2) - based solar cells efficiency decrease for wide band gap (high Ga content), we have performed a series of samples by PVD using the three stage process. The average compositions of our solar cells range from x = 0 to x = 0.88, as measured by X-ray diffraction. An important feature of this process is to create a double Ga gradient into the absorber, which contributes to improve efficiencies, and this has a major impact on the determination of the sample composition from x-ray diffraction data. We have developed a model in order to assess this impact and question the validity of the compositions extracted from x-ray data. This model allows to get some information about gradient shapes. Using our model, we have obtained some insights on the evolution of the gallium gradient in samples with increasing Ga content, and we determine that this gradient is less pronounced when increasing the amount of gallium. It is a well known fact that this gradient assists the extraction of photocreated carriers, and the modifications of the gallium profile that we have determined may explain, for some part, the degradation of solar cells efficiency for high gallium compositions.
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