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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Crystal structure of Cu2Zn(GexSi1−x)Se4 solid solution: the kesterite to wurtz–kesterite structural phase transition

Developing low-cost, sustainable, and environmentally friendly top absorber layers for tandem solar cells is essential to advancing photovoltaic technologies and accelerating the transition to renewable energy. In this work, we explore the potential of tetravalent (Cu2Zn(GexSi1−x)Se4) cation mutations in chalcogenide compound semiconductors with the aim of finding a material with increased band gap and reduced structural disorder. A combination of high-resolution synchrotron powder diffraction and neutron powder diffraction was used to determine the atomic positions and monoclinic angles in monoclinic wurtz–kesterite type Cu2Zn(GexSi1−x)Se4 mixed crystals as well as to determine the cation distribution in the crystal structure of Ge-rich kesterite-type and Si-rich wurtz–kesterite type mixed crystals. These investigations enabled us to deduce the structural transition scenario within the Cu2Zn(GexSi1−x)Se4 series. The transition occurs via a region where two phases with different crystal structures, tetragonal and monoclinic and thus a different distortion of the coordination tetrahedra, but the same cation distribution within the element specific cation sites co-exist. Thus, the structural transition between the kesterite and the wurtz–kesterite structure within the Cu2Zn(GexSi1−x)Se4 series is a distortion driven transition. The study identifies cation mutation in quaternary chalcogenides as a promising strategy beyond chalcopyrites and kesterites for low cost and environmentally friendly top absorbers in tandem solar cells.

Gurieva, Galina [Helmholtz Center Berlin for Mater↗
DOE OSTI2025

Alkali triel chalcogenide nanocrystals: a molecular reactivity approach to ternary phase selectivity

Alkali-metal-based materials are promising building blocks for energy conversion and storage technologies. Here, we use a molecular reactivity-based solution-phase approach to selectively synthesize multiple phases and specific polymorphs of lithium- and sodium-containing triel chalcogenide nanocrystals, LiTrCh 2 , NaTrCh 2 , and NaTr 3 Ch 5 , where Tr = Ga and In and Ch = S, Se, and Te. Analogous to the case of binary II–VI and III–V tetrahedral semiconductors, where the two commonly isolated zinc blende and wurtzite polymorphs are separated by only 1–50 meV f.u. −1 , we find that LiTrCh 2 nanocrystals easily adopt tetragonal (chalcopyrite) and orthorhombic polymorphs separated by only 2.7–6.2 meV f.u. −1 Because of this small energy difference, soft colloidal synthesis succeeds in accessing either one of these polymorphs, depending on the specific dichalcogenide precursor used. Highly reactive diethyl diselenide favors the thermodynamically more stable tetragonal I$\bar{4}2$d phase, whereas mildly reactive diphenyl diselenide favors the kinetic, metastable orthorhombic Pna2 1 phase. Density functional theory calculations confirm the relative energies among multiple LiTrCh 2 polymorphs and also model the observed powder X-ray diffraction pattern of a new C2 NaIn 3 Te 5 phase. 7 Li, 69 Ga, and 77 Se solid-state NMR spectra are consistent with phase-pure ternary LiGaSe 2 nanocrystals. A majority of the nanocrystal compositions are visible-light emitters. This work opens the door to new Li/Na-based ternary triel chalcogenide nanostructures for energy storage and conversion applications.

Pavel, Md Riad Sarkar [Iowa State Univ., Ames, IA ↗
DOE OSTI2020

Impact of UV-induced ozone and low-energy Ar + -ion cleaning on the chemical structure of Cu(In,Ga)(S,Se) 2 absorber surfaces

Dry buffer layer deposition techniques for chalcopyrite (CIGSSe)-based thin-film solar cells lack the surface-cleaning characteristics of the commonly used CdS or Zn(O,S) wet-chemical bath deposition. Here, a UV-induced ozone and/or a low-energy Ar + -ion treatment could provide dry CIGSSe surface cleaning steps. To study the impact of these treatments, the chemical surface structure of a CIGSSe absorber is investigated. For this purpose, a set of surface-sensitive spectroscopic methods, i.e., laboratory-based x-ray photoelectron spectroscopy and x-ray-excited Auger electron spectroscopy, is combined with synchrotron-based soft x-ray emission spectroscopy. After treatment times as short as 15 s, the UV-induced ozone treatment decreases the amount of carbon adsorbates at the CIGSSe surface significantly, while the oxygen content increases. This is accompanied by the oxidation of all absorber surface elements, i.e., indium, selenium, sulfur, and copper. Short (60 s) low-energy Ar + -ion treatments, in contrast, primarily remove oxygen from the surface. Longer treatment times also lead to a removal of carbon, while extremely long treatment times can also lead to additional (likely metallic) Cu phases at the absorber surface as well.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

CIGS photovoltaics: reviewing an evolving paradigm

Copper indium selenide chalcopyrite-structure alloys with gallium (CIGS) are unique among the highest performing photovoltaic (PV) semiconductor technologies. They are structurally disordered, nonstoichiometric materials that have been engineered to achieve remarkably low bulk nonradiative recombination levels. Nevertheless, their performance can be further improved. This review adopts a fundamental thermodynamic perspective to comparatively assess the root causes of present limitations on CIGS PV performance. The topics of selectivity and passivation of contacts to CIGS and its multinary alloys are covered, highlighting pathways to maximizing the electrochemical potential between those contacts under illumination. Further, an overview of absorber growth methods and resulting properties is also provided. We recommend that CIGS researchers consider strategies that have been successfully implemented in the more mature wafer-based GaAs and Si PV device technologies, based on the paradigm of an idealized PV device design using an isotropic absorber with minimal nonradiative recombination, maximal light trapping, and both electron-selective and hole-selective passivated contacts. We foresee that CIGS technology will reach the 25% efficiency level within the next few years through enhanced collection and reduced recombination. To significantly impact power-generation applications, cost-effective, manufacturable solutions are also essential.

14 SOLAR ENERGY↗
DOE OSTI2021

Mg x Zn 1−x O contact to CuGa 3 Se 5 absorber for photovoltaic and photoelectrochemical devices

Abstract CuGa 3 Se 5 is a promising candidate material with wide band gap for top cells in tandem photovoltaic and photoelectrochemical (PEC) devices. However, traditional CdS contact layers used with other chalcopyrite absorbers are not suitable for CuGa 3 Se 5 due to the higher position of its conduction band (CB) minimum. Mg x Zn 1− x O (MZO) is a transparent oxide with adjustable band gap and CB position as a function of magnesium composition, but its direct application is hindered by CuGa 3 Se 5 surface oxidation. Here, MZO is investigated as a contact (n-type ‘buffer’ or ‘window’) material to CuGa 3 Se 5 absorbers pretreated in Cd 2+ solution, and an onset potential close to 1 V vs reversible hydrogen electrode in 10 mM hexaammineruthenium (III) chloride electrolyte is demonstrated. The Cd 2+ surface treatment changes the chemical composition and electronic structure of the CuGa 3 Se 5 surface, as demonstrated by photoelectron spectroscopy measurements. The performance of CuGa 3 Se 5 absorber with Cd 2+ treated surface in the solid-state test structure depends on the Zn/Mg ratio in the MZO layer. The measured open circuit voltage of 925 mV is promising for tandem PEC water splitting with CuGa 3 Se 5 /MZO top cells.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Quasilinear dispersion in electronic band structure and high Seebeck coefficient in CuFeS 2 -based thermoelectric materials

The earth-abundant natural mineral chalcopyrite CuFeS 2 is a potential n-type thermoelectric material because of its large Seebeck coefficient at high carrier concentrations. For a long time, the large Seebeck coefficient of CuFeS 2 has been attributed to a large electron effective mass, but the reasons for this and the unusual carrier concentration dependent behavior have rarely been discussed. Here, we systematically investigated the special transport behavior of CuFeS 2 and found the classical parabolic band model to be inadequate in explaining it. Our experimental and theoretical studies indicate that there are two flat electronic pockets at the and Z points of the Brillouin zone near the conduction band edge of CuFeS 2 that dominate the charge transport. These electronic pockets result from nonparabolic quasilinearly dispersing bands that give rise to a linear wave vector dependent energy (E ~ k) and a carrier density dependent effective mass (m* ~ m 0 n 1/3 ). Such a strong carrier concentration dependent carrier effective mass results in the high Seebeck coefficient of CuFeS 2 compound under a large carrier density. Here, the work demonstrates that quasilinearly dispersing bands can give strongly enhanced Seebeck coefficient, and could be useful in optimizing the properties of thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Electronic structure and exchange interactions in altermagnetic MnGeP 2 in the quasiparticle self-consistent G W approach

The quasiparticle self-consistent 𝐺⁡𝑊 method is used to study the electronic band structure, optical dielectric function, and exchange interactions in chalcopyrite, 𝐼⁢ ‾ 4 ⁢2⁢𝑑, structure MnGeP 2 . The material is found to be an antiferromagnetic semiconductor with a lowest direct gap of 2.44 eV at the Γ point and a lower indirect gap of 1.87 eV from Γ to 𝑀. The material is an altermagnet because the two magnetic atoms of opposite spin are related by a twofold rotation operation perpendicular to the main fourfold rotation inversion axis. The spin splittings along a low symmetry line like 𝑃⁢𝑁 is sizable while at k points on the diagonal mirror planes or on the twofold symmetry axes the spin splitting is zero. The exchange interactions are calculated using a linear response approach. The antiferromagnetic exchange interaction between nearest neighbors in the primitive unit cell is dominating and found to be slightly decreasing upon carrier doping but not sufficiently to change the interaction to become ferromagnetic. The bare (noninteracting) and interacting transverse spin susceptibilities, which provide interatomic site exchange interactions after averaging over the muffin-tin spheres, are calculated from the 𝐺⁡𝑊 band structure and wave functions. From these exchange interactions, the spin wave spectra are obtained along the high symmetry lines and the Néel temperature is calculated using the mean-field and Tyablikov estimations. The dielectric function and the optical absorption spectra are calculated including excitonic effects using the Bethe Salpeter equation. The exchange interactions around Mn Ge defect sites is also studied. While we find it can generate ferromagnetic interactions with neighboring spins, we did not find direct evidence of producing an overall ferromagnetic phase. First, if Mn antisites are introduced by exchanging Mn with a nearby Ge, the interactions stay largely antiferromagnetic. Second, when we add additional Mn, in other words in Mn-rich stoichiometry, the Mn Ge antisites produce a strong ferromagnetic interaction primarily with the Mn in the same basal plane but weaker ferromagnetic interaction with adjacent plane Mn. The interactions between regular lattice Mn stay antiferromagnetic as before and thus favor keeping the antiferromagnetic order along the [001] direction. Adding Mn antisites, however, does lead to a metallic band structure.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Cobalt mineralogy at the Iron Creek deposit, Idaho cobalt belt, USA: Implications for domestic critical mineral production

Current U.S. policies aim to establish domestic supply chains of critical minerals for the energy transition. The Iron Creek deposit in the Idaho cobalt belt (ICB) is one of the most promising cobalt (Co) targets. Our case study illustrates the importance of mineralogy in strategic evaluations of critical mineral potential. Most of the Co at Iron Creek occurs as Fe substitution in pyrite, with lattice-bound and inclusion-hosted Ag, As, Bi, Ni, Pb, Se, Te ± trace Au and Sb. Cobalt also occurs in minor cattierite-vaesite. The Co minerals are intergrown with Co-poor chalcopyrite hosting Cu ± minor In and Zn. Worldwide, most Co is recovered from deposits mineralogically distinct from the ICB, and the United States currently lacks infrastructure to recover this Co and its associated metals. ICB ore minerals could be processed by autoclave, roaster, smelter, bioleach, or heap leach. Recovery of the Ag, As, Au, Bi, In, Pb, Se, Te, and Zn would be costly by autoclave, and construction of a custom smelter for ICB ores is likely uneconomic, so these elements would become waste irrespective of criticality. The Co-Fe and Co-As sulfide minerals are most suitable for Co and Ni recovery by a hydrometallurgical autoclave process, with potential pretreatment of cobaltiferous pyrite/arsenopyrite in an inert-atmosphere roaster, in new domestic or anticipated international facilities. The ICB is the second largest known Co resource in the United States. Consideration of ore mineralogy in the ICB is essential in strategies for domestic production.

58 GEOSCIENCES↗
DOE OSTI2020

Materials Data on CdSnSb2 by Materials Project

CdSnSb2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Cd2+ is bonded to four equivalent Sb3- atoms to form CdSb4 tetrahedra that share corners with four equivalent CdSb4 tetrahedra and corners with eight equivalent SnSb4 tetrahedra. All Cd–Sb bond lengths are 2.86 Å. Sn4+ is bonded to four equivalent Sb3- atoms to form SnSb4 tetrahedra that share corners with four equivalent SnSb4 tetrahedra and corners with eight equivalent CdSb4 tetrahedra. All Sn–Sb bond lengths are 2.87 Å. Sb3- is bonded to two equivalent Cd2+ and two equivalent Sn4+ atoms to form corner-sharing SbCd2Sn2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CuBS2 by Materials Project

CuBS2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Cu1+ is bonded to four equivalent S2- atoms to form CuS4 tetrahedra that share corners with four equivalent CuS4 tetrahedra and corners with eight equivalent BS4 tetrahedra. All Cu–S bond lengths are 2.28 Å. B3+ is bonded to four equivalent S2- atoms to form BS4 tetrahedra that share corners with four equivalent BS4 tetrahedra and corners with eight equivalent CuS4 tetrahedra. All B–S bond lengths are 1.95 Å. S2- is bonded to two equivalent Cu1+ and two equivalent B3+ atoms to form corner-sharing SCu2B2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAgSe2 by Materials Project

AgAlSe2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Ag1+ is bonded to four equivalent Se2- atoms to form AgSe4 tetrahedra that share corners with four equivalent AgSe4 tetrahedra and corners with eight equivalent AlSe4 tetrahedra. All Ag–Se bond lengths are 2.68 Å. Al3+ is bonded to four equivalent Se2- atoms to form AlSe4 tetrahedra that share corners with four equivalent AlSe4 tetrahedra and corners with eight equivalent AgSe4 tetrahedra. All Al–Se bond lengths are 2.43 Å. Se2- is bonded to two equivalent Ag1+ and two equivalent Al3+ atoms to form corner-sharing SeAl2Ag2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAgTe2 by Materials Project

AgAlTe2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Ag1+ is bonded to four equivalent Te2- atoms to form AgTe4 tetrahedra that share corners with four equivalent AgTe4 tetrahedra and corners with eight equivalent AlTe4 tetrahedra. All Ag–Te bond lengths are 2.82 Å. Al3+ is bonded to four equivalent Te2- atoms to form AlTe4 tetrahedra that share corners with four equivalent AlTe4 tetrahedra and corners with eight equivalent AgTe4 tetrahedra. All Al–Te bond lengths are 2.66 Å. Te2- is bonded to two equivalent Ag1+ and two equivalent Al3+ atoms to form corner-sharing TeAl2Ag2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TlCuS2 by Materials Project

CuTlS2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Cu1+ is bonded to four equivalent S2- atoms to form CuS4 tetrahedra that share corners with four equivalent CuS4 tetrahedra and corners with eight equivalent TlS4 tetrahedra. All Cu–S bond lengths are 2.31 Å. Tl3+ is bonded to four equivalent S2- atoms to form TlS4 tetrahedra that share corners with four equivalent TlS4 tetrahedra and corners with eight equivalent CuS4 tetrahedra. All Tl–S bond lengths are 2.64 Å. S2- is bonded to two equivalent Cu1+ and two equivalent Tl3+ atoms to form corner-sharing STl2Cu2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TlCuSe2 by Materials Project

CuTlSe2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Cu1+ is bonded to four equivalent Se2- atoms to form CuSe4 tetrahedra that share corners with four equivalent CuSe4 tetrahedra and corners with eight equivalent TlSe4 tetrahedra. All Cu–Se bond lengths are 2.43 Å. Tl3+ is bonded to four equivalent Se2- atoms to form TlSe4 tetrahedra that share corners with four equivalent TlSe4 tetrahedra and corners with eight equivalent CuSe4 tetrahedra. All Tl–Se bond lengths are 2.76 Å. Se2- is bonded to two equivalent Cu1+ and two equivalent Tl3+ atoms to form corner-sharing SeTl2Cu2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiBO2 by Materials Project

LiBO2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Li1+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All Li–O bond lengths are 1.98 Å. B3+ is bonded to four equivalent O2- atoms to form corner-sharing BO4 tetrahedra. All B–O bond lengths are 1.49 Å. O2- is bonded in a 4-coordinate geometry to two equivalent Li1+ and two equivalent B3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MgSiN2 by Materials Project

MgSiN2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Mg2+ is bonded to four equivalent N3- atoms to form MgN4 tetrahedra that share corners with four equivalent MgN4 tetrahedra and corners with eight equivalent SiN4 tetrahedra. All Mg–N bond lengths are 2.11 Å. Si4+ is bonded to four equivalent N3- atoms to form SiN4 tetrahedra that share corners with four equivalent SiN4 tetrahedra and corners with eight equivalent MgN4 tetrahedra. All Si–N bond lengths are 1.76 Å. N3- is bonded to two equivalent Mg2+ and two equivalent Si4+ atoms to form corner-sharing NMg2Si2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BeCN2 by Materials Project

BeCN2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Be2+ is bonded to four equivalent N3- atoms to form BeN4 tetrahedra that share corners with four equivalent BeN4 tetrahedra and corners with eight equivalent CN4 tetrahedra. All Be–N bond lengths are 1.70 Å. C4+ is bonded to four equivalent N3- atoms to form CN4 tetrahedra that share corners with four equivalent CN4 tetrahedra and corners with eight equivalent BeN4 tetrahedra. All C–N bond lengths are 1.50 Å. N3- is bonded to two equivalent Be2+ and two equivalent C4+ atoms to form corner-sharing NBe2C2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BeSiN2 by Materials Project

BeSiN2 is Chalcopyrite structured and crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Be2+ is bonded to four equivalent N3- atoms to form BeN4 tetrahedra that share corners with four equivalent BeN4 tetrahedra and corners with eight equivalent SiN4 tetrahedra. All Be–N bond lengths are 1.78 Å. Si4+ is bonded to four equivalent N3- atoms to form SiN4 tetrahedra that share corners with four equivalent SiN4 tetrahedra and corners with eight equivalent BeN4 tetrahedra. All Si–N bond lengths are 1.75 Å. N3- is bonded to two equivalent Be2+ and two equivalent Si4+ atoms to form corner-sharing NBe2Si2 tetrahedra.

36 MATERIALS SCIENCE↗