Reaction pathway to Cu2ZnSnSe4 formation in CdI2

Journal of Thermal Analysis and Calorimetry - We investigated various possible chemical interactions between individual precursor compounds (ZnSe, SnSe, and CuSe) and CdI2 as a flux material used...     

Temperature-dependent photoreflectance of SnS crystals

The optical properties of single-crystal SnS were studied by photoreflectance (PR) spectroscopy. Temperature-dependent PR spectra were measured in the range 20–200 K. A room-temperature bandgap energy value of E_g=1.317 eV was estimated by fitting the temperature dependence of the bandgap energy obtained from the PR spectra. The vibrational properties of orthorhombic SnS were studied using Raman spectroscopy. Four vibrational modes were detected at 95, 163, 191, and 218 cm^–1.     

Cu2ZnSnSe4 formation and reaction enthalpies in molten NaI starting from binary chalcogenides

The present study deals with chemical reactions and enthalpies during the synthesis of Cu₂ZnSnSe₄ (CZTSe) from CuSe, SnSe, and ZnSe in molten NaI as flux material in closed degassed ampoules. Differential thermal analysis (DTA) at heating rates 5 °C min^?1 and cooling rates 10 °C min^?1 were used for the determination of temperatures of phase transitions and/or chemical reactions. XRD and Raman analyses confirmed that the formation of CZTSe starts already at 380 °C after the melting of Se that deliberates from the transformation of CuSe to Cu_1.8Se, and the CZTSe formation process impedes to a great extent due to the presence of solid NaI. After the melting of NaI, the formation of CZTSe is completed. For the determination of enthalpy values, the calibration with pure NaI was performed. The thermal effects and enthalpies were compared with the available known thermodynamical values. The specific enthalpy of exothermic Cu₂ZnSnSe₄ formation at 661 °C in NaI ?36 ± 3 kJ mol^?1 was determined experimentally for the first time. Ternary compound Na₂SnSe₃ was formed during the synthesis process. NaI·2H₂O, if present in NaI, was found to be a critical issue in the synthesis process of CZTSe monograin powders in molten NaI—it gave rise to the formation of oxygen-containing by-products Na₂SeO₄ and Na₂Cu(OH)₄. The complete dehydration of NaI·2H₂O at T ≤ 70 °C in vacuum is necessary to avoid the formation of oxygen-containing compounds.     

Cu2ZnSnSe4 films by selenization of Sn–Zn–Cu sequential films

This paper deals with the formation of Cu₂ZnSnSe₄ (CZTS) in the process of selenization of metal precursor layers in elemental selenium vapour. Metallic precursors were sequentially evaported from Sn, Zn and Cu sources. Precursor Sn–Zn–Cu films have a “mesa-like” structure and consist mainly of Cu₅Zn₈ and Cu₆Sn₅ phases. It was confirmed that the formation of different binary copper selenides is the dominating process of selenization in elemental Se vapour at temperatures up to 300 °C. The formation of kesterite CZTS films begins at 300 °C and dominates at higher temperatures, always resulting in multiphase films that consist of high-quality Cu₂ZnSnSe₄ crystals and of a separate phase of ZnSe.     

Photoluminescence study of disordering in the cation sublattice of Cu2ZnSnS4

In this study we investigated the influence of the degree of disordering in the cation sublattice on low temperature photoluminescence (PL) properties of Cu₂ZnSnS₄ (CZTS) polycrystals. The degree of disordering was changed by using different cooling rates after post-annealing at elevated temperatures. The results suggest that in the case of higher degree of cation sublattice disorder radiative recombination involving defect clusters dominates at T = 10 K. These defect clusters induce local band gap energy decrease in CZTS. The concentration of defect clusters can be reduced by giving more time for establishing ordering in the crystal lattice. As a result, radiative recombination mechanism changes and band-to-impurity recombination involving deep acceptor defect with ionization energy of about 200 meV starts to dominate in the low temperature PL spectra of CZTS polycrystals.