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Parameterization of CuIn1-xGaxSe2 (x=0, 0.5, and 1) energy bands
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.ORCID iD: 0000-0002-9050-5445
2011 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 21, 7503-7507 p.Article in journal (Refereed) Published
Abstract [en]

Parameterization of the electronic band structure of CuIn(1-x)Ga(x)Se(2) (x=0, 0.5, and 1) demonstrates that the energy dispersions of the three uppermost valence bands [E(j)(k); j=v1, v2, and v3] are strongly anisotropic and non-parabolic even very close to the Gamma-point valence-band maximum E,(0). Also the lowest conduction band E(c1) (k) is anisotropic and non-parabolic for energies similar to 0.05 eV above the band-gap energy. Since the electrical conductivity depends directly on the energy dispersion, future electron and hole transport simulations of CuIn(1-x)Ga(x)Se(2) need to go beyond the parabolic approximation of the bands. We therefore present a parameterization of the energy bands, the k-dependency of the effective electron and hole masses m(f)(k), and also an average energy-dependent approximation of the masses m(j)(E).

Place, publisher, year, edition, pages
2011. Vol. 519, no 21, 7503-7507 p.
Keyword [en]
CuInSe(2), CuGaSe(2), Chalcopyrite, Solar cells, Band structure, Electronic structure, Effective mass
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-45289DOI: 10.1016/j.tsf.2010.12.216ISI: 000295347700088Scopus ID: 2-s2.0-80052151715OAI: oai:DiVA.org:kth-45289DiVA: diva2:452239
Funder
Swedish Research Council
Note

QC 20111028

Available from: 2011-10-28 Created: 2011-10-28 Last updated: 2017-05-23Bibliographically approved
In thesis
1. Exploring the Electronic and Optical Properties of Cu(In,Ga) Se2
Open this publication in new window or tab >>Exploring the Electronic and Optical Properties of Cu(In,Ga) Se2
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. vii, 63 p.
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-160949 (URN)978-91-7595-453-0 (ISBN)
Presentation
2015-03-06, Sal N111, Brinellvägen 23, KTH, Stockholm, 11:00 (English)
Opponent
Supervisors
Note

QC 20150305

Available from: 2015-03-05 Created: 2015-03-05 Last updated: 2015-03-09Bibliographically approved
2. First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials
Open this publication in new window or tab >>First-Principles Study on Electronic and Optical Properties of Copper-Based Chalcogenide Photovoltaic Materials
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To accelerate environmentally friendly thin film photovoltaic (PV) technologies, copper-based chalcogenides are attractive as absorber materials. Chalcopyrite copper indium gallium selenide (CIGS ≡ CuIn1–xGaxSe2) is today a commercially important PV material, and it is also in many aspects a very interesting material from a scientific point of view. Copper zinc tin sulfide selenide (CZTSSe ≡ Cu2ZnSn(S1–xSex)4) is considered as an emerging alternative thin film absorber material. Ternary Cu2SnS3 (CTS) is a potential absorber material, thus its related alloys Cu2Sn1–xGexS3 (CTGS) and Cu2Sn1–xSixS3 (CTSS) are attractive due to the tunable band gap energies. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 can be potential as ultra-thin (≤ 100 nm) film absorber materials in the future. In the thesis, analyses of these Cu-based chalcogenides are based on first-principles calculations performed by means of the projector augmented wave method and the full-potential linearized augmented plane wave formalisms within the density functional theory as implemented in the VASP and WIEN2k program packages, respectively.

The electronic and optical properties of CIGS (x = 0, 0.5, and 1) are studied, where the lowest conduction band (CB) and the three uppermost valence bands (VBs) are parameterized and analyzed in detail. The parameterization demonstrates that the corresponding energy dispersions of the topmost VBs are strongly anisotropic and non-parabolic even very close to the Γ-point. Moreover, the density-of-states and constant energy surfaces are calculated utilizing the parameterization, and the Fermi energy level and the carrier concentration are modeled for p-type CIGS. We conclude that the parameterization is more accurate than the commonly used parabolic approximation. The calculated dielectric function of CuIn0.5Ga0.5Se2 is also compared with measured dielectric function of CuIn0.7Ga0.3Se2 collaborating with experimentalists. We found that the overall shapes of the calculated and measured dielectric function spectra are in good agreement. The transitions in the Brillouin zone edge from the topmost and the second topmost VBs to the lowest CB are responsible for the main absorption peaks. However, also the energetically lower VBs contribute significantly to the high absorption coefficient.

CTS and its related alloys are explored and investigated. For a perfectly crystalline CTS, reported experimental double absorption onset in dielectric function is for the first time confirmed by our calculations. We also found that the band gap energies of CTGS and CTSS vary almost linearly with composition over the entire range of x. Moreover, those alloys have comparable absorption coefficients with CZTSSe. Cu2XSnS4 (X = Be, Mg, Ca, Mn, Fe, Ni, and Zn) are also studied, revealing rather similar crystalline, electronic, and optical properties. Despite difficulties to avoid high concentration of anti-site pairs disordering in all compounds, the concentration is reduced in Cu2BeSnS4 partly due to larger relaxation effects. CuSb(Se1–xTex)2 and CuBi(S1–xSex)2 are suggested as alternative ultra-thin film absorber materials. Their maximum efficiencies considering the Auger effect are ~25% even when the thicknesses of the materials are between 50 and 300 nm.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 97 p.
Keyword
density functional theory, electronic structure, dielectric function, absorption coefficient, copper-based chalcogenides, ultra-thin film
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-207626 (URN)978-91-7729-396-5 (ISBN)
Public defence
2017-06-12, Sal D3, Lindstedtsvägen 5, Stockholm, 13:15 (English)
Opponent
Supervisors
Note

QC 20170523

Available from: 2017-05-23 Created: 2017-05-22 Last updated: 2017-05-24Bibliographically approved

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