Direct vapour transport grown Cu2SnS3 crystals: exploring structural, elastic, optical, and electronic properties

Copper tin sulphide (Cu2SnS3) (CTS) has emerged as a potent material for applications in photovoltaic, thermoelectric, electrochemical, biological, and other fields. CTS has superior properties such as non-toxicity, direct bandgap, p-type conductivity, variable crystal structure, alterable morphology and ease of synthesis, and it is a better substitute for conventional semiconductor materials. In the present work, CTS crystals were grown using direct vapour transport. Investigation through X-ray diffraction showed that the as-grown CTS crystals possessed a cubic unit cell structure with a = b = c = 5.403 Å. The analysis of the binding energies and composition of constituents of the as-grown CTS crystals via X-ray photoelectron spectroscopy confirmed the presence of Cu1+, Sn4+ and S2-. The experimental bandgap of CTS crystals is 1.23 eV, which was confirmed by diffuse reflectance spectroscopy. The investigation of elastic, optical, thermal and electronic properties of CTS crystals was carried out via density functional theory employing generalized gradient approximation with the Perdew-Burke-Ernzerhof exchange-relationship functional. The first-ever analysis of the temperature-dependent elastic properties of CTS crystals revealed greater stability at elevated temperature (953 K). Dielectric properties, reflectivity, refractive index, loss function, extinction and absorption coefficients of CTS crystals were computed and analyzed in detail. The evaluation of the electronic band structure with density of states revealed valence band maximum and conduction band energy level contributions, showing a bandgap of 1.2 eV. The obtained results are discussed in detail.

Emission tuning of highly efficient quaternary Ag-Cu-Ga-Se/ZnSe quantum dots for white light-emitting diodes

With the blooming development of zero-dimensional nanomaterials, I-III-VI alloying quantum dots (QDs) with outstanding photoelectrical properties have emerged to attract much attention as promising environmentally-friendly substitutions for conventional binary Cd-based QDs. In this work, a facile one-pot method was introduced to synthesize unreported quaternary Ag-Cu-Ga-Se/ZnSe (ACGSe/ZnSe) QDs. A relatively high photoluminescence quantum yield (PL QY) of 71.9% and a tunable emission from 510 to 620 nm were successfully achieved. We explored the roles of alloying compositions in ACGSe/ZnSe QDs, inferring that increased Ag proportion would not only lower the V_defect level which leads to the blue shift of emission, but also slow the ZnSe shelling process owing to the larger lattice distortion. At last, the white light-emitting diodes (WLEDs) were fabricated with ACGSe/ZnSe QDs as the conversion layer, indicating that the as-prepared QDs are a promising candidate for further applications.

Aqueous synthesis of composition-tuned defects in CuInSe2 nanocrystals for enhanced visible-light photocatalytic H2 evolution

The composition and defect tolerance of CuInSe₂ (CISe) quantum dots (QDs) provide a scaffold to design defects via tailoring the elemental ratio or distributions for boosting photocatalytic H₂ evolution (PHE). Herein, a ligand-assisted two-step aqueous method was developed to prepare defect CISe quantum dots for the first time. UV-vis, XPS, HRTEM, and HADDF investigations confirmed the typical double-absorption edges of copper vacancy defects and indium substituted at copper site defects in the structure constructed through initial synthesis tuned by Cu/In ratio and the ensued coarsening. The steady-transient PL suggested that the D-A recombination with prolonged PL lifetime dominated the emission of composition-optimized CuInSe₂ with the Cu/In ratio of 1/4 (CISe-1/4). Further transient photocurrent and electrochemical impedance spectroscopy investigations demonstrated that surface defects in the structure favor the carriers' separation/transportation. The CISe-1/4 exhibited a superior PHE rate of 722 μmol g^-1 h^-1, about 23 times higher than that of the initially synthesized CISe-1/4 nucleus (31 μmol g^-1 h^-1), with a maximum apparent quantum efficiency (AQE) of 1.3%. The analysis of energy levels and the coulombic interaction energy of electron-hole (J _e/h) based on Raman, extending UV-vis spectra investigations suggested that surface defects resulted in decreased J _e/h of CISe-1/4, favoring the enhanced PHE of this structure. This work is expected to provide a reference for designing effective non-noble metal I-III-VI photocatalysts.

Ternary metal selenide/MWCNT/PANI: potential n-type nanohybrids for room-temperature thermoelectric applications

Lead-free novel n-type ternary nanohybrids were fabricated by blending separately synthesized, diamond like I-III-VI₂ and I-V-VI₂ (I-Cu, Ag, III-In, V-Sb, VI-Se) nanocrystals (NCs) in a multi-walled carbon nanotube (MWCNT) and polyaniline (PANI) matrix. A thermoelectric study of these nanohybrids was performed at room temperature in order to understand their utility as potential thermoelectric materials for advanced applications. Electrical conductivity, thermal conductivity and Seebeck coefficient were measured and the thermoelectric performance was evaluated at room temperature. All ternary nanohybrids revealed an n-type behavior with relatively higher electrical conductivity in the order of 10³ S m^-1. Among the CuInSe₂ (CIS), AgInSe₂ (AIS) and CuSbSe₂ (CSS)-based hybrids, chalcostilbite (i.e., CSS/MWCNT/PANI) showed a good performance at room temperature with a power factor of 1.16 μW m^-1 K^-2 and Seebeck coefficient of -23.5 μV K^-1. A possible mechanism of the charge transport for the ternary hybrid was also discussed. The present article highlights the potentiality of different lead-free ternary metal selenide NPs in hybrid forms for thermoelectric applications.

Solution based synthesis of Cu(In,Ga)Se2 microcrystals and thin films

Herein, for the first time, we report the synthesis of quaternary Cu(In,Ga)Se₂ microcrystals (CIGSe MCs) using a facile and economical one-pot heating-up method. The most important parameters such as reaction temperature and time were varied to study their influences on the structural, morphological, compositional and optical properties of the MCs. Based on the results, the formation of CIGSe was initiated from binary β-CuSe and then converted into pure phase CIGSe by gradual incorporation of In³⁺ and Ga³⁺ ions into the β-CuSe crystal lattice. As the reaction time increases, the band gap energy was increased from 1.10 to 1.28 eV, whereas the size of the crystals increased from 0.9 to 3.1 μm. Besides, large-scale synthesis of CIGSe MCs exhibited a high reaction yield of 90%. Furthermore, the CIGSe MCs dispersed in the ethanol was coated as thin films by a drop casting method, which showed the optimum carrier concentration, high mobility and low resistivity. Moreover, the photoconductivity of the CIGSe MC thin film was enhanced by three order magnitude in comparison with CIGSe NC thin films. The solar cells fabricated with CIGSe MCs showed the PCE of 0.59% which is 14.75 times higher than CIGSe NCs. These preliminary results confirmed the potential of CIGSe MCs as an active absorber layer in low-cost thin film solar cells.

Herein, for the first time, we report the synthesis of quaternary Cu(In,Ga)Se₂ microcrystals (CIGSe MCs) using a facile and economical one-pot heating-up method.

Titanium dioxide (TiO2)-decorated silver indium diselenide (AgInSe2): novel nano-photocatalyst for oxidative dye degradation

Novel titanium-dioxide-decorated silver indium diselenide nano-photocatalyst for enhancement in photocatalytic dye degradation efficiency of three different dyes, namely, MB, MO, and RhB.