Showing papers by "Peter Baláž published in 2018"

Semi-industrial Green Mechanochemical Syntheses of Solar Cell Absorbers Based on Quaternary Sulfides

Abstract: Stannite Cu2FeSnS4 and kesterite Cu2ZnSnS4 were synthesized by an eco-friendly ball-milling method in an industrial mill. Both synthesized sulfides represent perspective materials in solar cell technology. Several characterization methods have been applied to determine the course of solid state mechanochemical reactions leading to the synthesis of potential chalcogenide solar cell absorbers. The phase and surface composition, solid state kinetics, and surface morphology of these quaternary sulfides were elucidated by the methods of X-ray diffractometry, X-ray photoelectron spectroscopy, Soxhlet analysis, and scanning electron microscopy. The application of eccentric vibration mills for these syntheses constitutes the big challenge for researchers in the field of photovoltaics in their permanent effort in scaling up new materials and processes.

Mechanochemically driven amorphization of nanostructurized arsenicals, the case of β-As4S4

Abstract: The amorphization is studied in mechanically activated β-As4S4 using high-energy ball milling in a dry mode with 100–600 min−1 rotational speeds, employing complementary methods of X-ray powder diffraction (XRPD) related to the first sharp diffraction peak, positron annihilation lifetime (PAL) spectroscopy, and ab initio quantum-chemical simulation within cation-interlinking network cluster approach (CINCA). The amorphous substance appeared under milling in addition to nanostructurized β-As4S4 shows character XRPD halos parameterized as extrapolation of the FSDPs, proper to near-stoichiometric amorphous As–S alloys. The structural network of amorphized arsenicals is assumed as built of randomly packed multifold cycle-type entities proper to As4S4 network. The depressing and time-enhancing tendency in the PAL spectrum peak is direct indicative of milling-driven amorphization, associated with free-volume evolution of interrelated positron- and Ps-trapping sites. At lower speeds (200–500 min−1), these changes include Ps-to-positron trapping conversion, but they attain an opposite direction at higher speed (600 min−1) due to consolidation of β-As4S4 crystallites. In respect of CINCA modeling, the effect of high-energy milling is identified as destruction–polymerization action on monomer cage-type As4S4 molecules and existing amorphous phase, transforming them to amorphous network of triple-broken As4S4 derivatives. These findings testify in a favor of “shell” kinetic model of solid-state amorphization, the amorphous phase continuously generated under speed-increased milling being identified as compositionally authentic to arsenic monosulfide, different in medium range ordering from stoichiometric As2S3.

Mechanochemical approach to a Cu2ZnSnS4 solar cell absorber via a “micro-nano” route

Abstract: The present study demonstrates a mechanochemical “micro-nano” approach toward the future solar cell absorber material Cu2ZnSnS4 (CZTS) with up-scaling potential. For this purpose, synthetic copper sulfide CuS and tin sulfide SnS nanoparticles along with microsized zinc metal and elemental sulfur as solid precursors were utilized. These precursors were milled in a planetary ball mill in an argon atmosphere for a period of 1–240 min. Moreover, we compare it to a “micro” approach starting from the elements and maintaining the same milling conditions. The phase composition of reaction mixtures was analyzed by X-ray diffractometry. The final products of syntheses were further analyzed by means of scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–Vis spectroscopy. The phase purity of the prepared materials was verified by confocal Raman microscopy. In both cases, a polydisperse system of a nearly stoichiometric Cu2ZnSnS4 phase was readily obtained after 60 min of milling with only traces of unreacted Cu2−xS phases. Based on the results, we conclude there is no definite difference in reaction speed. However, the crystallite size and optical properties of the prepared CZTS samples slightly differ when various precursors are used.

Rapid mechanochemical synthesis of nanostructured mohite Cu2SnS3 (CTS)

Abstract: Rapid solvent-free mechanochemical synthesis of CTS nanocrystals from elemental precursors is reported herein. The process is completed in 15 min, proceeding through immediate formation of CuS in a self-sustaining manner and its subsequent reaction with Sn and residual sulfur. The reaction progress was monitored by pressure and temperature changes in the milling vessel, X-ray diffraction, Soxhlet analysis, grain size analysis and electric resistivity measurements. The relationship between the consumption of metallic precursors, grain size and electrical resistivity is provided. The final product was nanocrystalline with crystallite size below 10 nm, as confirmed by both X-ray diffraction and transmission electron microscopy. The nanocrystals are agglomerated into micrometer-sized grains. It exhibits poor porous properties with the specific surface area value of 2.5 m2/g. The X-ray photoelectron spectroscopy has shown that the surface is significantly oxidized, due to milling in air. The optical properties of the prepared CTS nanocrystals are interesting for photovoltaic applications.

Free-volume structure of glass-As2Se3/PVP nanocomposites prepared by mechanochemical milling

Abstract: Atomic-deficient void structure is studied in nanocomposites prepared by mechanochemical milling of glassy g-As2Se3 in a water solution of polyvinylpyrrolidone (PVP) employing positron annihilation lifetime spectroscopy. Formalism of Ps-to-positron trapping conversion known as x3-x2-CDA (coupling decomposition algorithm) is applied to identify free-volume defects in the pelletized g-As2Se3/PVP nanocomposite in respect to dry-milled g-As2Se3 one. Under wet-milling, the inter-nanoparticle Ps-decaying sites in preferential PVP environment replace free-volume positron traps (in dry-milled g-As2Se3) with defect-specific lifetime of 0.352 ns, corresponding to di-/tri-atomic vacancies in g-As-Se.