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Flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells show great potential applications due to low-cost, nontoxicity, and stability. The device performances under an especial open circuit voltage (VOC) are limited by the defect recombination of CZTSSe/CdS heterojunction interface. We improve the deposition technique to obtain compact CdS layers without any pinholes for flexible CZTSSe solar cells on Mo foils. The efficiency of the device is improved from 5.7% to 6.86% by highquality junction interface. Furthermore, aiming at the S loss of CdS film, the S source concentration in deposition process is investigated to passivate the defects and improve the CdS film quality. The flexible Mo-foil-based CZTSSe solar cells are obtained to possess a 9.05% efficiency with a VOC of 0.44 V at an optimized S source concentration of 0.68 mol/L. Systematic physical measurements indicate that the S source control can effectively suppress the interface recombination and reduce the VOC deficit. For the CZTSSe device bending characteristics, the device efficiency is almost constant after 1000 bends, manifesting that the CZTSSe device has an excellent mechanical flexibility. The effective improvement strategy of CdS deposition is expected to provide a new perspective for promoting the conversion efficiency of CZTSSe solar cells. [ABSTRACT FROM AUTHOR]

This paper systematically investigates the local distortion and electron paramagnetic resonance (EPR) parameter for CdCl2:V2+ and CdCl2:V2+ systems on the basis of the complete energy matrix, in which not only the contributions due to the spin-orbit coupling of the central ions but also that of the ligands are considered. To describe the difference of overlapping between d-orbits and p orbit, two spin-orbit coupling coefficients are introduced. By simulating the crystal field parameter and EPR parameter, the local distortion parameters are studied and the relationships between the EPR parameter and the spin-orbit coupling coefficients as well as divergent parameter are discussed. These results show that the local structures exhibit compression distortion for CdCl2:V2+ and elongation distortions for CdCl2:V2+, respectively. It notes that the empirical formula R ≈ RH + (ri-rh)=2 is not suitable for CdCl2:V2+ and CdCl2:V2+ systems. The contributions of ligand to spin-orbit coupling interaction cannot be neglected for strong covalent systems, especially for V2+ doped in CsMgBr3:V2+. [ABSTRACT FROM AUTHOR]

The geometries, electronic structures and related properties of SimN8-m(0 < m < 8) clusters are studied using density functional theory (DFT) with hybrid functional B3LYP. The calculated results reveal several trends. For any stoichiometric clusters, the lowest energy isomers with an alteration of N and Si atoms are favourable in energy if the numbers of Si and N atoms are large enough to form ... Si-N-Si-N... alternative chains. The bond lengths of single Si-N bonds are very close to the corresponding values of the bulk and other Si-N clusters. The geometries for N-rich and Si4N4 clusters are planar structures, but three-dimensional structures are favourable in energy for Si-rich clusters. With the increase of m, the isotropic polarizability and average polarizability increase, the total binding energies generally decrease, the HOMO-LUMO gap and vertical ionization potential oscillate with increasing number of valence electrons, and their values with even valence electrons are larger than those with odd valence electrons. The atomic charges, IR and Raman properties are also reported. [ABSTRACT FROM AUTHOR]