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The crystalline structural, electronic and optical properties of the alloys Cu2ZnSn1− xGe xS4, Cu2ZnSn1− xSi xS4, Cu2ZnSn1− xGe xSe4 and Cu2ZnSn1 −xSi xSe4 are calculated by first-principles using both the generalized gradient approximation and a hybrid functional approach. We find that the electronic band structures are qualitatively very similar for these alloys. The band-gap energy Eg( x) (for x = 0, 0.125, 0.25, 0.5, 0.75, 0.875 and 1) increases almost linearly with Ge and Si substitution. However, for very Si rich Cu2ZnSn1− xSi xS4 alloys (but not for Cu2ZnSn1 −xSi xSe4) there is an abrupt increase of Eg( x) for x > 0.96. We therefore analyse this effect by calculating the electronic structures for x = 0.93, 0.96 and 1. We find that the Sn-like states form localised density-of-states below the conduction band edge in Cu2ZnSn1 −xSi xS4, while corresponding states resonate more with the conduction bands in Cu2ZnSn1− xSi xSe4. The effect in S-based alloys is a direct consequence of the energetically high conduction band edge for Cu2ZnSiS4 in combination with energetically low Sn-like states. Furthermore, the calculated dielectric constants are relatively similar for all alloy configurations. Overall however, our results suggest that it is possible to use Si and Ge as alloying element in quaternary Cu2ZnSnS4 to improve the photovoltaic properties. [ABSTRACT FROM AUTHOR]

To accelerate environmental friendly thin-film photovoltaic technologies, earth-abundant, non-toxic, and low-cost materials are demanded. We study the compounds of Cu2Sn1 −xGe xS3 and Cu2Sn1− xSi xS3 ( x = 0, 0.5, and 1) employing first-principles method within the density functional theory. The compounds have comparable band dispersions. The band-gap energies Eg can be tailored by cation alloying the Sn atoms with Ge or Si. The gap energies of Cu2Sn1− xGe xS3 and Cu2Sn1− xSi xS3, with x = 0, 0.5, and 1, vary almost linearly from 0.83 to 1.43 eV and 2.60 eV, respectively. However, the gap energy of Cu2SiS3 does not follow the linear relation for x > 0.8. The effective electron masses at the Γ-point of the lowest conduction band are almost isotropic for all materials, which are between 0.15 m0 and 0.25 m0. On the other hand, the effective hole masses of the topmost valence band show very strong anisotropy for all compounds. In the (010) direction, the hole masses are estimated to be between 1.01 m0 and 1.85 m0, while between 0.11 m0 and 0.41 m0 in the (001) direction. Calculations reveal that all compounds have high absorption coefficients that are comparable with that of Cu2ZnSnS4. The absorptions in the energy region from Eg + 0.5 eV to Eg + 1.0 eV are even higher for Ge- and Si-alloying of Cu2SnS3, compared with Cu2ZnSnS4. The high-frequency dielectric constants of the compounds are between 6.8 and 8.9. Cu2Sn1− xGe xS3 and Cu2Sn1− xSi xS3 can be considered as potential candidates for absorber materials in thin-film solar cells. [ABSTRACT FROM AUTHOR]

In this work, we determine experimentally the dielectric function of monoclinic Cu 2 SnS 3 (CTS) by spectroscopic ellipsometry from 0.7 to 5.9 eV. An experimental approach is proposed to overcome the challenges of extracting the dielectric function of Cu 2 SnS 3 when grown on a glass/Mo substrate, as relevant for photovoltaic applications. The ellipsometry measurement reveals a double absorption onset at 0.91 eV and 0.99 eV. Importantly, we demonstrate that calculation within the density functional theory (DFT) confirms this double onset only when a very dense k -mesh is used to reveal fine details in the electronic structure, and this can explain why it has not been reported in earlier calculated spectra. We can now show that the double onset originates from optical transitions at the Γ -point from three energetically close-lying valence bands to a single conduction band. Thus, structural imperfection, like secondary phases, is not needed to explain such an absorption spectrum. Finally, we show that the absorption coefficient of CTS is particularly large in the near-band gap spectral region when compared to similar photovoltaic materials. [ABSTRACT FROM AUTHOR]

Abstract: Parameterization of the electronic band structure of CuIn1−x Ga x Se2 (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 Γ-point valence-band maximum E v1(0). Also the lowest conduction band E c1(k) is anisotropic and non-parabolic for energies ~ 0.05eV above the band-gap energy. Since the electrical conductivity depends directly on the energy dispersion, future electron and hole transport simulations of CuIn1−x Ga x Se2 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 j (k), and also an average energy-dependent approximation of the masses m j (E). [Copyright &y& Elsevier]

Electrochemical carbon dioxide (CO 2 ) reduction for C 2 products has been studied on a series of supported Cu-based catalysts; however, the charge-promotion effects from the substrates for the selectivity of CO 2 reduction are still unclear. Here we localize nanosized Cu 2 O on three carbon-based substrates that provide different charge-promotion effects: positively charged boron-doped graphene (BG), negatively charged nitrogen-doped graphene (NG), and weak negatively charged reduced graphene oxide (rGO). We demonstrate that the charge-promotion effects lead to an increase in faradaic efficiency (FE) for C 2 products with an order of rGO/Cu < BG/Cu < pure Cu < NG/Cu and an FE C 2 /FE C 1 ratio from 0.2 to 7.1. By performing in situ characterization, electrokinetic investigations, and density functional theory (DFT) calculations, we reveal that the negatively charged NG is favorable for stabilizing Cu + species under CO 2 reduction, which strengthens CO* adsorption to further boost C-C coupling for C 2 products. As a result, we achieve a high C 2+ FE of ∼68% at high current densities of 100-250 mA cm -2 .

Electrochemical production of hydrogen peroxide (H 2 O 2 ) from O 2 on single-atom catalysts has attracted great attention, yet the quest for robust catalysts is driven by achieving >90 % Faradaic efficiency (FE) under industrial-relevant current densities (>100 mA cm -2 ). Herein we synthesize a catalyst that contains single nickel site coordinated by four nitrogen and two oxygen atoms (i.e., N 4 Ni 1 O 2 ) via involving carboxyl functionalized multiwall carbon nanotubes as a substrate to provide extra O coordination to the regular NiN 4 site. It has a cathodic energy efficiency of approximately 82 % and a H 2 O 2 FE of around 96 % at 200 mA cm -2 current density, outperforming the reported single-atom catalysts for H 2 O 2 electrosynthesis., (© 2022 Wiley-VCH GmbH.)

Copper (Cu)-based metal-organic frameworks (MOFs) and MOF-derived catalysts are well studied for electroreduction of carbon dioxide (CO 2 ); however, the effects of organic linkers for the selectivity of CO 2 reduction are still unrevealed. Here, a series of Cu-based MOF-derived catalysts is investigated with different organic linkers appended, named X-Cu-BDC (BDC = 1,4-benzenedicarboxylic acid, X = NH 2 , OH, H, F, and 2F). It is found that the linkers affect the faradaic efficiency (FE) for C 2 products with an order of NH 2  < OH < bare Cu-BDC < F < 2F, thus tuning the FE C2 :FE C1 ratios from 0.6 to 3.8. As a result, the highest C 2 FE of ≈63% at a current density of 150 mA cm -2 on 2F-Cu-BDC derived catalyst is achieved. Using operando Raman measurements, it is revealed that the MOF derives to Cu 2 O during eCO 2 RR but organic linkers are stable. The fluorine group in organic linker can promote the H 2 O dissociation to *H species, further facilitating the hydrogenation of *CO to *CHO that helps CC coupling., (© 2022 Wiley-VCH GmbH.)

Background: Phosphoactivation of a DNA damage response molecule checkpoint kinase 2 (pChk2) may be a marker of oral epithelial cells that have entered the precancerous and squamous cell carcinoma (SCC) stages. We explored whether there was selective expression of pChk2 in precancerous lesions but not in nonneoplastic tissue of the oral mucosa., Experimental Design: In a retrospective cohort design, 96 biopsied clinical leukoplakias and erythroplakias with known subsequent progression to SCC were identified from 48 subjects and assigned as the cases group. Expression status of pChk2 was compared with that of the 97 leukoplakias and erythroplakias that did not progress to SCC (control groups) by immunohistochemical analysis. Included in both groups were lesions with histologically confirmed dysplasia and those that lacked histologic evidence of atypia., Results: Subjects with pChk2-positive but histology-negative (for atypia) lesions had an 8.6 times higher risk of developing SCC compared with those with pChk2-negative and histology-negative lesions. Overall, the presence of detectable pChk2 staining was able to identify lesions at risk of developing SCC within 3 years with a sensitivity of 85.2%, specificity of 74.2%, and predictive accuracy of 78.2% (odds ratio, 19.9; 95% confidence interval, 7.3-55.5)., Conclusion: This is the first study to include histologically nonatypical cases in the analysis of a putative biomarker for oral precancerous lesions. Our data show that pChk2 merits further investigation as a promising biomarker that can discriminate those lesions at risk for developing SCC, regardless of histologic evidence for atypia.