SEMI-INDUSTRIAL GREEN MECHANOCHEMICAL SYNTHESES OF

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Semi-industrial green mechanochemical syntheses of solar cell absorbers based on quaternary sulfides Peter Balàž, Michal Hegedus, Marcela Achimovicova, Matej Baláž, Matej Tešinský, Erika Dutkova, Mária Ka#uchová, and Jaroslav Brian#in ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03563 • Publication Date (Web): 10 Jan 2018 Downloaded from http://pubs.acs.org on January 10, 2018

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ACS Sustainable Chemistry & Engineering

SEMI-INDUSTRIAL GREEN MECHANOCHEMICAL SYNTHESES OF SOLAR CELL ABSORBERS BASED ON QUATERNARY SULFIDES (Dedicated to the memory of Professor Eberhard Gock) Peter Baláž1, Michal Hegedüs2*, Marcela Achimovičová1,4, Matej Baláž1, Matej Tešínsky1, Erika Dutková1, Mária Kaňuchová3, Jaroslav Briančin1 1

Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 04001 Košice, Slovakia 2 Institute of Chemistry, Faculty of Science, P. J. Šafárik University in Košice, Moyzesova 11, 04001 Košice, Slovakia 3 Institute of Earth Resources, Faculty of Mining, Ecology, Process control and Geotechnologies, Technical University in Košice, Letná 9, 04001 Košice, Slovakia 4 Institute of Mineral and Waste Processing, Waste Disposal and Geomechanics, University of Technology, 38678 Clausthal, Germany Corresponding Author *M. Hegedüs. Tel: 421-918-666-136; E-mail: [email protected] ABSTRACT Stannite Cu2FeSnS4 and kesterite Cu2ZnSnS4 were synthesized by ecofriendly 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. KEYWORDS Solid-state reactions, mechanochemistry, scalable synthesis, advanced materials, photovoltaics, stannite, kesterite

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INTRODUCTION Solar energy represents the best alternative as an eco-friendly and inexhaustible clean energy in comparison with the energy obtained from traditional exhaustible fossil fuels. Until now, the effort to gain electrical energy from current photovoltaic panels was more expensive in comparison with traditional thermal treatment of fossil fuels. The effort to optimize the solar materials is therefore urgent 1–8. Among the quaternary chalcogenides Cu(Inx,Ga1-x)(S,Se)2 (CIGS) thin films represent an interesting option, as in their case, more than 20% efficiency is achieved 9. However, the main CIGS drawbacks are: Se toxicity, In and Ga economy, and their abundance. Therefore, an effort to find analogous materials must be backed-up by selection of ecofriendly and cheap precursors for synthesis. Stannite Cu2FeSnS4 and wellelaborated kesterite Cu2ZnSnS4 with their promising photoelectric properties represent alternatives to CIGS. Recent technological status for the CIGS preparation follows a two-step approach comprising a low temperature precursor deposition and subsequent high temperature selenization/sulfidisation annealing 10. However, several excellent papers were published recently where application of high-energy milling has been described as an effective way for preparation of new compounds via solid-state synthesis. This laboratory approach can produce advanced materials within the frame of inorganic and organic chemistry. The application in material science heterogenous catalysis, pharmaceutical and medicinal chemistry can serve as a good illustration 11–24. In energy-related topics like solar cells and thermoelectric materials this trend is also strongly visible. Kesterite Cu2ZnSnS4, stannite Cu2FeSnS4, and other quaternary sulfides have recently proved to be effective on a laboratory scale according to several papers 25–31. However, this eco-friendly and solvent-free synthesis approach needs validation for production of materials in scalable amounts. Vibration mills and their industrially successful alternative - eccentric vibration mills (ESM) represent a suitable option of high energy mills. Theory and practical application of ESM are closely bound with works of Professor Gock and his co-workers 32– 36 . The ESM mills have modular tube design in which the exciter unit consisting of a bearing block and unballance masses are connected to the motor by means of the drive shaft. For the purpose of mass compensation, a counterweight is located on the opposite side to the exciter unit. The major technological advance is the fixed amplitude of vibration up to 20 mm (normally 12 mm maximum) and eliptical, circular, and linear vibrations in comparison with circular vibrations in conventional mills. Except of „traditional“ applications in mineral processing, hydrometallurgy, soil rehabilitation, pharmaceutical industry, and agriculture, etc. where ESMs were applied for mechanical activation of solids. They could be also used in „advanced“ applications as mechanochemical reactors to produce new compounds. In this case, solid state reactions are executed directly in the mill. 2 ACS Paragon Plus Environment

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The aim of this paper is to illustrate effectiveness of an industrial eccentric vibration mill for mechanochemical synthesis of two quaternary sulfides suitable as perspective absorbers in solar cells. MATERIALS AND METHODS Materials For mechanochemical synthesis various precursors were applied. Copper (99% Merck, Germany), iron (99% Winlab, Germany), zinc (99% Aldrich, Germany), tin (99% Nihon Seiko, Japan) and sulphur (99% CG-Chemikalien, Germany) powders were used as elemental precursors. Natural CuFeS2 (98%, deposit Zhezkazgan, Kazakhstan, JCPDS 00-035-0752), mechanochemically synthesized copper sulfide CuS (JCPDS 00-006-0464) and tin sulfide SnS (JCPDS 00-039-0354) were used as precursors. Mechanochemical synthesis Mechanochemical solid state syntheses were performed in an industrial eccentric vibratory ball mill ESM 656-0.5 ks (Siebtechnik, Germany) working under following conditions: 5L steel satellite milling chamber attached to the main corpus of the mill, tungsten carbide balls with a diameter of 35 mm with a total mass 30 kg, 80% ball filling, amplitude of the mill 20 mm, rotational speed of the eccenter 960 min-1, argon atmosphere, the feed 100 grams. The milling was performed at various times. In case of mechanochemical synthesis of CuS and SnS precursors, milling for 40 and 60 min, respectively, has been applied. The photographs of the mill with satellite are given in Figure 1. Stoichiometric ratios of precursors have been applied according to reactions given in part Results and Discussion.

Figure 1. Eccentric vibratory mill with attached closed satellite (left), the open satellite filled with balls (right).



Characterization techniques X-ray diffractometry (XRD) The identification of phase composition was performed by XRD method with an X´Perth PW 3040 MPD diffractometer (Phillips, Germany) working in the 2θ geometry with CuKα radiation. Photoelectron spectroscopy (XPS) XPS measurements of samples were performed using XPS instrument SPECS equipped with PHOIBOS 100 SCD and non-monochromatic X-ray source. The survey surface spectrum was measured at 70 eV pass energy and the core spectra at 20 eV at room temperature. All spectra were acquired at a basic pressure of 1.10-8 mbar with AlKα excitation at 10 kV (200 W). The data were analysed by SpecsLab2 CasaXPS software (Casa Software Ltd). A Shirley and Tougaard type baseline was used for all peak-fits. The spectrometer was calibrated against silver (Ag 3d). All samples showed variable degree of charging. The problem was resolved by the calibration on carbon. UV-Vis spectroscopy (UV-Vis) UV-Vis spectra were collected using the UV-Vis spectrophotometer Helios Gamma (Thermo Electron Corporation, Great Britain) working in the range 200900 nm in quartz cell by dispersing of synthesized particles in absolute ethanol by ultrasonic stirring for 10 min. Scanning electron microscopy (SEM) SEM images of the samples were recorded using MIRA3 FE-SEM microscope (TESCAN, Czech Republic) equipped with EDX detector (Oxford Instrument, United Kingdom). Soxhlet analysis The content of non-reacted elemental sulphur in the samples was determined by a gravimetric method using a Soxhlet extractor. The extraction thimble was loaded with 1 g of powder sample and placed into the main chamber of the extractor. 30 mL of carbon disulfide (99.9%, Fischer Chemical) was placed into a 500 mL distilling flask and the apparatus was set up. Upon heating of the distilling flask in a hot water bath, three cycles were run to quantitatively dissolve all sulphur present in the sample. The resulting solution cooled to a room temperature was transferred into a 250 mL round bottom flask of a known mass and the solvent was distilled under vacuum. The flask was further dried at 70°C to eliminate any traces of the solvent and re-weighed. Conversion degree α of the corresponding mechanochemical synthesis was calculated based on Soxhlet analysis according to the formula 4 ACS Paragon Plus Environment

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= 1 −

(1)

where α is overall conversion degree, mso - the starting amount of sulphur in the reaction mixture (g), mf1 – mass of the flask after extraction (g), mf0 – mass of the flask before extraction (g).

RESULTS AND DISCUSSION In this part we evaluate various mechanochemical pathways to synthesize stannite Cu2FeSnS4 and kesterite Cu2ZnSnS4 in an industrial scale for solar cell absorbers. Methods of XRD (phase analysis), XPS (surface composition), SEM (morphology), Soxhlet analysis (kinetics) and UV-Vis (band gap calculation) were applied as the main identification and characterization tools. Stannite Cu2FeSnS4 Synthesis from copper mineral and synthetic compounds Chalcopyrite CuFeS2 mineral in combination with tin sulfide SnS and copper sulfide CuS compounds were applied for mechanochemical synthesis of stannite. Overal hypothetical equation of the synthesis can be proposed in form CuFeS2 + CuS + SnS → Cu2FeSnS4 (2) Reaction mixture corresponding to the stoichiometry of equation (2) was milled for 60, 120 and 240 minutes, respectively. X-ray diffractograms are given in Figure 2. All XRD patterns are strongly influenced by amorphization and formation of small crystallites. Stannite Cu2FeSnS4 (JCPDS 00-044-1476) is identified already at the shortest milling time (60 min), Fig. 2A. However, its identification is complicated because the main peak is overlapped by other peaks of unreacted chalcopyrite CuFeS2 (JCPDS 00-035-0752) and covellite CuS (JCPDS 00-024-0060). Unreacted herzenbergite SnS (JCPDS 00-014-0620) is also present. The further progress of reaction (2) is manifested by more diffused XRD peaks and absence of SnS in XRD spectra. However, rhodostannite Cu2FeSn3S8 (JCPDS 00-029-0558) as further stannite phase can be identified by milling for 240 min. The mechanism of the new phase formation is even more complicated, because already at 120 min the additional quaternary sulfide mawsonite Cu6Fe2SnS8 (JCPDS 00-029-0557) starts to be present.



Figure 2. XRD patterns of the powders milled according to eq. 2 for different times.

X-ray photoelectron spectroscopy was used to elucidate the surface composition of as-synthesized powders. High resolution XPS spectra are shown in Figure 3. Fig. 3A shows the most intensive copper binding peaks at 932.10 eV and 951.70 eV with a peak splitting of 19.8 eV. Undoubtedly, the splitting confirms Cu+ oxidation state in non-consumed chalcopyrite 37. However, the region 932.0-932.4 eV is also typical for Cu2+ in CuS 38 which is also well suited for the first peak in Fig. 3A. The surface iron is represented by peaks at 711.06 eV, 715.66 eV and 724.99 eV (Fig. 3B). The spectrum is in a good agreement with the values for Fe2+ ion with the binding energy of 710.3 eV and 723.5 eV, respectively 39. Peaks at 494.50 eV and 503.05 eV and a peak splitting of 8.6 eV in Fig. 3C indicates presence of Sn4+ ion in the structure 40. Peak at 161.85 eV (Fig. 3D) is consistent with the values 160-164 eV expected for S2- in sulfide phases 41.


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Figure 3. High-resolution XPS spectra of the powder milled according to eq. 2 for 240 min : A-copper, B-iron, C-tin, D-sulphur.

Figure 4 shows SEM images for low and high magnification of sample milled for 240 min. It is evident that the sample is formed by particles of different sizes where tendency to form microagglomerates can be seen (Fig. 4A). By larger magnification, submicron particles can be traced. These are also agglomerates composed of nanoparticles in the form of plates (Fig. 4B).

Figure 4. SEM images of the powder milled according to eq. 2 for 240 min.



Synthesis from synthetic compounds and elements Compounds tin sulfide SnS and copper sulfide CuS in combination with elements Fe and S were applied for mechanochemical synthesis of stannites. Overal hypothetical equation of the synthesis can be proposed in form 2CuS + SnS + Fe + S → Cu2FeSnS4 (3) Reaction mixture corresponding to the stoichiometry of equation (3) was milled for 30, 60, 120, 240 and 480 minutes, respectively. X-ray diffractograms for all milled samples are shown in Figure 5. They illustrate progress of reaction (3). At the shortest milling times only reaction precursors can be traced (Fig. 5A and 5B). At 120 min of milling the picture is changed: the pattern is more simple and the product stannite Cu2FeSnS4 (JCPDS 00-035-1351) is already seen for the first time (Fig. 5C). However, traces of covellite CuS (JCPDS 00-039-0354) and herzenbergite SnS (JCPDS 00-0039-0354) are still present. Non-consumed elemental iron used as precursor in reaction (3) is clearly seen. There is not a big difference between Fig. 5C and Fig. 5D showing XRD patterns for powders milled for 240 and 480 min. However, in both cases, rhodostannite Cu2FeSn3S8 (JCPDS 00-021-0878) is already present as a second stannite phase. The XRD patterns presented in Fig 5C and 5D are strongly influenced by amorphization as a consequence of prolonged milling. By mutual comparison of Fig. 5C and Fig. 5D it can be stated that the products are more pronounced (see the most intensive peak) and non-reacted Fe is present in a small amount only.


Equation (1) has been applied to calculate the conversion degree, α of stannite formation by milling. In Figure 6, the corresponding plot is given. Very 8 ACS Paragon Plus Environment

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high conversion degrees (over 94 %) can be obtained at 120 min and longer milling times. This quantitative statement is in a good accordance with qualitative data obtained from XRD measurements.

Figure 6. Conversion degree α vs. milling time for stannite synthesis (equation 3).

High resolution XPS spectra are given in Figure 7. Fig. 7A shows two most intensive copper binding peaks at 932.74 eV and 952.54 eV. There are also intermittent peaks at 937.07 eV and 944.42 eV. Undoubtedly, the most intensive peaks and a peak splitting of 19.8 eV belong to Cu+ ion configuration in stannite structure 42,43 as in Fig. 3A. Two smaller peaks correspond to Cu2+ ion configuration which forms satellites in the region 930-950 eV 44. The surface iron is represented by peaks at 710.79 eV, 715.09 eV and 724.82 eV (Fig. 7B). The spectrum is in a good agreement with the values for Fe2+ ion with the binding energy of 710.3 eV and 723.5 eV for Fe 2p levels 39. Peaks at 486.50 and 495.23 eV and a peak splitting of 8.7 eV in Fig. 7C indicates presence of Sn4+ 40. However, the first peak could be also assigned to Sn2+ configuration from non-consumed SnS. Peak at 161.46 eV in Fig. 7D is consistent with the span of values 160-164 eV expected for S2- configuration in stannite phases 41.



Figure 7. High resolution XPS spectra of the powder milled according to eq. 3 for 480 min: A-copper, B-iron, C-tin, D-sulphur.

SEM images of sample milled for 480 minutes are shown in Figure 8. Morphology reflects combination of micro and nanoparticles with tendency to form agglomerates (Fig. 8A). This tendency can be identified by higher magnification also for flat nanoparticles (Fig. 8B).



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Synthesis from elements Elements Cu, Fe, Sn and S were applied for mechanochemical synthesis of stannites. Overall hypothetical equation of the synthesis can be proposed in form 2Cu + Sn + Fe + 4S → Cu2FeSnS4 (4) Reaction mixture corresponding to the stoichiometry of equation (4) was milled for 60, 120 and 240 minutes, respectively. XRD patterns are given in Figure 9. Already at the shortest milling time (Fig. 9A) stannite Cu2FeSnS4 (JCPDS 00-044-1476 ) is present as a product of reaction (4). However, also other present phases like copper sulfide CuS (JCPDS 00-006-0464), iron sulfide FeS (JCPDS 00-023-1123) and non-consumed Sn (JCPDS 00-004-0673) complet the whole picture. The presence of binary sulfides CuS and FeS confirms that the mechanism of stannite formation proceeds through the intermediate step. The presence of spionkopite Cu1.39S (JCPDS 00-036-0380) as an intermediate is questionable but can be connected with non-stoichiometry in Cu-S system 45. After prolonged milling for 120 min (Fig. 9B) the XRD pattern is more simplified and only stannite phases can be detected. No impurity peaks from reaction precursors were observed in the diffraction pattern. Rhodostannite Cu2FeSn3S8 is formed as a product of stannite transformation. There is no difference for this pattern and a pattern of sample milled for 240 min (Fig. 9C). Stannite to rhodostannite transformation during milling represents a new phenomenon which has been studied in a more detail in our latest work 31.

Figure 9. XRD patterns of the milled according to eq. 4 for different times.



X-ray photoelectron spectroscopy was used to elucidate the surface composition of as synthesized powders. High resolution XPS spectra are given in Figure 10. Fig. 10A shows two most intensive copper binding peaks at 932.74 eV and 952.54 eV. There is also an intermittent coupling between these two peaks. Undoubtedly, the most intensive peaks and a peak splitting of 19.8 eV belongs to Cu+ ion configuration in stannite structure 42,46. Two peaks with lower intensity correspond to Cu2+ ion configuration which forms satellites in the region 930-950 eV 44. The surface iron (Fig. 10B) is represented by peaks at 711.68 eV and 725.16 eV. Their splitting of 13.5 eV indicates the presence of Fe2+ ion 39. The peak at 716.83 eV belongs to Sn2+ configuration. Peaks at 486.50eV and 495.23 eV with a peak splitting of 8.7 eV in Fig. 10C which indicates the presence of Sn4+ 40. Peak at 161.46 eV in Fig. 10D is consistent with the span of values 160-164 eV expected for S2- configuration in stannite phases 41.

Figure 10. High-resolution XPS spectra of the powder milled according to eq. 3 for 240 min: A-copper, B-iron, C-tin, D-sulphur.

SEM images for the sample milled for 240 min are depicted in Figure 11. The strong tendency to create big agglomerates is evidenced again (Fig. 11A) together with preserved nanoparticles (Fig. 11B). As for particle size this is comparable with the size in Fig. 8B.


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The UV-Vis spectra of samples milled for 120 min and 240 min were studied using absorption UV-Vis spectroscopy and they are given in Figure 12. The as-synthesized samples exhibit a broad optical absorption in the visible wavelength region. The band gap was determined by plotting (Ahν)2 as a function of the photon energy (hν) and extrapolating the linear portion of the spectrum in the band edge region, as shown in the inset of Fig. 12. The obtained values of the optical band gap are almost comparable with the previous results reported in the literature 42.



Figure 12. UV-Vis spectra and Tauc plots (the variation of (Ahv)2 vs. hν shown in the inset) for samples according to eq. 3 milled for 120 and 240 min.

Kesterite Cu2ZnSnS4 Synthesis from elements Until now, mechanochemical synthesis of kesterite Cu2ZnSnS4 has been studied using various compounds as precursors in laboratory mill. Mainly chlorides and sulfides were applied 47–50. In our case, elements Cu, Zn, Sn and S were applied for mechanochemical synthesis in an semi-industrial mode. Overal hypothetical equation of the synthesis can be proposed in form 2Cu + Zn + Sn + 4 S → Cu2ZnSnS4 (5) Reaction mixture corresponding to the stoichiometry of equation (5) was milled for 60, 120 and 240 minutes, respectively. Corresponding XRD patterns are given in Fig. 13. Already at the shortest milling time (Fig. 13A) kesterite Cu2ZnSnS4 (JCPDS 00-026-0575) is present as a product of reaction (5). However, there is a plenty of other peaks in XRD pattern which do not correspond to kesterite phase. Non-reacted Sn (JCPDS 00-004-0673), Zn (JCPDS 00-004-0831) and covellite CuS (JCPDS 00-006-0464) complet X-ray diffractogram. As in previous case, the presence of CuS confirms a hypothesis that the mechanism of kesterite formation proceeds through an intermediate step 14 ACS Paragon Plus Environment

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where binary precursors susceptible for synthesis via milling are being formed first. The high reactivity of mechanochemical synthesis of CuS from elemental precursors has been verified recently 51. After prolonged milling for 120 min (Fig. 13B), the XRD pattern is simpler. Finally, at milling time 240 min (Fig. 13C) kesterite phase is dominant and only small amount of other phases like elemental Sn can be traced. Unambiguously, elemetal Zn is still present. The further research is needed to complete the reaction (5). According to Park its presence implies that the product can have Zn-deficient phase formed through the consumption of CuS and elemental Sn 52.


High resolution XPS spectra are shown in Figure 14. Fig. 14A shows two most intensive copper binding peaks at 932.63 eV and 952.23 eV. The peak positions and the peak separation of 19.6 eV indicate the presence of Cu+ configuration in kesterite structure 47. There is also week intermittent peak at 942.09 eV which belongs to Cu2+ 47. The surface zinc is represented in Fig. 14B by peaks at 1021.74 eV and 1034.95 eV. The peak at higher binding energy corresponds to Zn2+ 46,53. The second peak belongs to unreacted elemental zinc which can be also traced in XRD pattern (Fig. 13). Peaks at 487.22 eV and 495.79 eV with a separation of 8.6 eV in Fig. 14C indicate presence of Sn4+ 53. Peaks at 163.27 eV and small sub-peak at approx. 160 eV in Fig. 14D are consistent with the span of values 160-164 eV expected for S2- configuration in kesterite nanocrystals 54.



Figure 14. High resolution XPS spectra of the powder milled according to eq. 4 for 240 min: A-copper, B-zinc, C-tin, D-sulphur.

SEM images of the samples milled according to equation (5) are shown in Figure 15. In comparison with previous SEM pictures for stannite system (Figures 4, 8 and 11), the tendency to form agglomerates is partly suppressed. However, in nanorange the particle sizes are comparable and more uniform size distribution can be expected. In confrontation with literature on mechanochemical synthesis of kesterite via milling of elemental precursors 52,53,55–57 , the common features can be found. The particles are always agglomerated to some extent. However, the careful study of milling time influence on particle morphology has shown that the milled samples illustrated transition from micron-sized particles to their sub-micron analogues 52.


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CONCLUSION In this work stannite Cu2FeSnS4 and kesterite Cu2ZnSnS4 were synthesized in an industrial eccentric vibratory mill. Various experimental approaches were applied for the synthesis using natural and synthetic precursors. Specifically, mineral CuFeS2, synthetic CuS and SnS, as well as Cu, Fe, Zn, Sn, and S elemental precursors were applied for stannite synthesis, and Cu, Zn, Sn and S for kesterite synthesis. Methods of XRD, XPS, and SEM were used for characterization of bulk, surface, and morphological properties of the synthesized products. The syntheses proceeded via intermediate products among which mainly binary sulfides were identified. The XPS results showed the presence of the elements in anticipated oxidation states and the SEM analysis revealed that all products were present in the form of nanoparticles agglomerated into larger grains. Method of Soxhlet analysis was applied in order to follow the reaction kinetics of stannite formation. For stannite synthesized from elemental precursors, the optical band gap energies were calculated. Particularly, the obtained values of Eg = 1.1-1.2 eV may be well suited for possible application of the synthesized materials as absorbers for solar cells. Generally, good recoveries have been obtained in mechanochemical reactions under study. However, the maintainance of purity of the obtained products still reamins a big challenge. There is a plethora methods usable for separation of unreacted species from quaternary sulfides composed of Cu, Fe, Zn, Sn, and S elements. Just to mention a few methods: (i) magnetic separation of non-reacted iron from produced stannite where a big difference in their magnetic susceptibilites can be presumed (ii) selective extraction of non-reacted sulfur via Soxhlet method 17 ACS Paragon Plus Environment


(iii) selective dissolution (e.g. FeS is soluble in dilute HCl in contrast to Cu) (iv) thermal post-treatment to remove non-reacted SnS Optimization of milling conditions such as milling time, frequency, and ball-to-powder ratio should be the very first step in mechanochemical synthesis before application of any mentioned methods aimed on the product purification. In optimized milling conditions it is possible that all precursors would be consumed in the course of the reaction. The synthesized quaternary sulfides contain only non-toxic and earthabundant components. The applied mechanochemical procedure can serve as a new way for low cost scaling in preparation of components for solar cells. ACKNOWLEDGEMENT This work was supported by the Slovak Research and Development Agency (project APVV-0103-14). The work was also performed within the European Community Horizon 2020 Programme, COST action CA15103 (CRM_EXTREME). The support of german Federal Ministry of Education and Research (Project IB-COMSTRUC-010) is also acknowledged. REFERENCES (1) (2)

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SYNOPSIS The effectiveness of high-energy milling brings in the new possibilities for scalable preparation of energetic materials via low-cost and solvent-free way.


SEMI-INDUSTRIAL GREEN MECHANOCHEMICAL SYNTHESES OF

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