Raman study of flash-lamp annealed aqueous Cu₂ZnSnS₄ nanocrystals

Abstract

The effect of flash-lamp annealing (FLA) on the re-crystallization of thin films made of colloidal Cu2ZnSnS4 nanocrystals (NCs) is investigated by Raman spectroscopy. Unlike similar previous studies of NCs synthesized at high temperatures in organic solvents, NCs in this work, which have diameters as small as 2–6 nm, were synthesized under environmentally friendly conditions in aqueous solution using small molecules as stabilizers. We establish the range of FLA conditions providing an efficient re-crystallization in the thin film of NCs, while preserving their kesterite structure and improving their crystallinity remarkably. The formation of secondary phases at higher FLA power densities, as well as the dependence of the formation on the film thickness are also investigated. Importantly, no inert atmosphere for the FLA treatment of the NCs is required, which makes this technology even more suitable for mass production, in particular for printed thin films on flexible substrates.

Phonon Raman spectroscopy of nanocrystalline multinary chalcogenides as a probe of complex lattice structures

“…The knowledge of EPC is particularly important for photovoltaic [32], thermoelectric, and luminescent properties [19,20,23,33]. Electronic resonances can be related with heterogeneity formed intentionally, as in core/shell NCs [27,28,[34][35][36][37][38][39], or with spontaneous formation of impurity phases in complex chalcogenide NCs [40][41][42][43][44][45][46]. In many cases, compositional and polymorphic imperfections cannot be discerned from the main phase by XRD or transmission electron microscopy (TEM) because of the close lattice parameters and similarity of the crystal symmetry.…”

Phonon Spectra of Strongly Luminescent Nonstoichiometric Ag–In–S, Cu–In–S, and Hg–In–S Nanocrystals of Small Size

“…Besides providing the phonon spectra themselves, Raman spectroscopy is an efficient tool of probing both the lattice structure of semiconductor NCs and local resonances. Such resonances can be related either with intentional heterogeneity, like in core/shell structures, − or spontaneous formation of secondary phases and other kinds of structural inhomogeneity in complex chalcogenide NCs, − which are not detectable by other structural techniques. These capabilities of Raman spectroscopy are based on spectrally well separated vibrational peaks related to different compounds, the possibility to selectively probe compounds/phases with different bandgaps by using resonant energy/wavelengths of the exciting light, and no special treatment of the sample needed for investigations.…”

Mathematical modelling of the conductivity in CZTiS-CZSnS as a function of synthesis temperature

“…With the conductivity data of tables 7 and 8, four mathematical models were adjusted by means of least squares equations ( 8) and ( 9), by ordinary differential equations dC/dT = kC(n − C), where (C) is the conductivity, (k) is constant of proportionality, (t) is the temperature and (n) maximum value of conductivity observed experimentally [40,41]. When solving it and using the initial conditions of conductivity given in the tables 8 and 9, equations (10) and (11) are obtained. These equations describe the electrical behavior of the two materials as a function of the synthesis temperature in terms of equations ( 8)- (11).…”

“…These models are a powerful tool for studying the behavior of electrochemical systems at present, they are widely used to evaluate various materials and the effect of synthesis conditions over its physicochemical properties, requiring the fulfillment of certain characteristics such as: causality, linearity, stability and finitude, that allows to eliminate inconsistent points of the analysis. Such modelling processes has been validated by implementing of Monte Carlo type error propagation methods, which consolidate remarkable levels of confidence in the experimental determination of properties such as the impedance, enabling analyze and classify the materials for future works [9][10][11]. Thus, the impedance data analysis with KK-type equations, allow to advance in models based on residuals, mean predictions and distances between estimated distributions, which could be used to evaluate the functions of electrical impedance improving the prediction of the conductivity in such materials in agreement with Liu et al [12].…”