Currently photovoltaics is becoming an established industrial field with the global installed capacity over 400 GWp, with perspective of reaching the terawatt installed capacity within the following decade. The field is dominated by silicon wafer based cells which reached the unforseen low systém prices. The advantages of silicon thin film based photovoltaics of lower consumption of semiconductors and shorter energy payback time was not sufficient to overcome the disadvantage of lower efficiencies (12 % record efficience vs. 25 %). The most recent record efficiencies are due to the combination of the two technologies: the interdigitated back contacted silicon heterojunction based cells reached 26.7 % efficiency by combining high quality wafer with very thin silicon films for preparing passivating selective contacts. In another parallel development silicon thin films make part of silicon nanowire based solar cells which the concept of geometrically thin - optically thick films with simple manufacturing. In our group we have contributed to the field by developing optical profilometry for nanometer thin films based on Raman spectroscopy [1], microscopic methods for characterizing the local properties of the silicon nanostructures [2] or for exploring photovoltaic materials [3] new ways of junction engineering by inserting 2D materials [4] or self-assembled dipolar molecule monolayers [5]. REFERENCES: [1] M. Ledinský, B. Paviet-Salomon, A. Vetushka, J. Geissbühler, A. Tomasi, M. Despeisse, S.D. Wolf, C. Ballif, A. Fejfar, Profilometry of thin films on rough substrates by Raman spectroscopy, Sci. Rep. 6 (2016) 37859. doi:10.1038/srep37859; [2] A. Fejfar, M. Hývl, A. Vetushka, P. Pikna, Z. Hájková, M. Ledinský, J. Kočka, P. Klapetek, A. Marek, A. Mašková, J. Vyskočil, J. Merkel, C. Becker, T. Itoh, S. Misra, M. Foldyna, L. Yu, P. Roca i Cabarrocas, Correlative microscopy of radial junction nanowire solar cells using nanoindent position markers, Sol. Energy Mater. Sol. Cells. 135 (2015) 106-112. doi:10.1016/j.solmat.2014.10.027; [3] L. Fanni, A.B. Aebersold, M. Morales Masis, M. Ledinsky, S. Escrig, A. Vetushka, D.T.L. Alexander, A. Hessler-Wyser, A. Fejfar, C. Hébert, S. Nicolay, C. Ballif, Direct Imaging of Dopant Distribution in Polycrystalline ZnO Films, ACS Appl. Mater. Interfaces. (2017). doi:10.1021/acsami.6b14350; [4] Z. Hájková, M. Ledinský, A. Vetushka, J. Stuchlík, M. Müller, A. Fejfar, M. Bouša, M. Kalbáč, O. Frank, Photovoltaic characterization of graphene/silicon Schottky junctions from local and macroscopic perspectives, Chem. Phys. Lett. 676 (2017) 82-88. doi:10.1016/j.cplett.2017.03.041; [5] A. Vetushka, L. Bernard, O. Guseva, Z. Bastl, J. Plocek, I. Tomandl, A. Fejfar, T. Baše, P. Schmutz, Adsorption of oriented carborane dipoles on a silver surface, Phys. Status Solidi B. (2015) n/a-n/a. doi:10.1002/pssb.201552446.
Nanocrystalline diamond (NCD) represents attractive material for the use in photovoltaic, energy storage, or biosensing applications. Thin NCD films can be deposited on various substrate materials using chemical vapor deposition. The substrate material is usually seeded with diamond nanopowder from which the diamond grains start to grow. Lateral structuring of such seeding layer can be used for selective growth of diamond structures and devices. However, reducing and controlling the pattern size and position on nano-scale as well as reducing unwanted growth outside the defined patterns is challenging. [Babchenko et al., Phys Status Solidi B 247 (2010)]
Instead of the lateral structuring and etching, a mask made of material suppressing spontaneous diamond nucleation can be used to achieve selective growth. In this contribution, we show that a-Si:H thin films completely suppress the spontaneous nucleation of diamond on samples. By contrast, the nucleation density (density of spontaneously nucleated diamond grains) on polished monocrystalline Si is relatively high (5×106 cm-2) under the same deposition conditions.
Thus, we cover the seeded substrate with a-Si:H thin film, which we pattern using photolithography process and dry chemical etching. We show that the diamond grows only on the parts of the sample, where the a-Si:H film has been removed, which is evidenced by SEM imaging and Raman micro-spectroscopy. The photoluminescence (PL) of NCD pattern was measured on micro-PL setup and analyzed with respect to color center contributions (SiV, NV). Further miniaturization is envisioned based on our recent work [Fait et al., Appl Surf Sci. 428 (2018)] using conductive AFM to prepare complex nanopatterns in the thin layer of a-Si:H with high precision and without any lithography steps.
ACKNOWLEDGEMENTS: The work was financially supported by the Czech Science Foundation project 17-19968S, CTU student project SGS18/179/OHK4/3T/13, and ERDF/MSMT project CZ.02.1.01/0.0/0.0/15_003/0000464.
Zinc oxide (ZnO) is a promising semiconductor material for optoelectronic devices. Due to its wide range of valuable properties, numerous devices from solar cells to light-emitting diodes have been developed. ZnO can be grown by a variety of techniques such as thermal oxidation, chemical bath deposition, and electrodeposition among others. However, most of the conventional ZnO growth requires high temperature systems, expensive equipment, and harmful chemicals. Likewise, these protocols involve complicated preparation methods to achieve high yields delaying the commercialization of ZnO nanomaterials. Herein, we demonstrate a facile and novel approach of generating nanostructured ZnO films through pH-controlled H2O oxidation. Vacuum-deposited Zn thin films were immersed in water at 90℃ with different pH values. Diverse nanostructures including particles, rods and tubes with different preferred growth orientations emerged. Enhanced transmittance and reduced band gap were observed for thicker nanostructured films. XRD and Raman spectra revealed that these structures had wurtzite ZnO crystal structure. In addition, room temperature photoluminescence showed that the nanorods and nanoparticles exhibited blue and orange emissions while the nanotubes displayed a green emission. XPS analysis indicated that the nanoparticles grown in an acidic water had the minimum hydroxyl group concentration. Based on our results, we propose that this technique can produce novel and high quality ZnO nanostructures that are applicable for flexible ZnO-based electronic devices.
NiMoO4 generates a broad interest as heterogeneous catalyst for gas phase selective oxidations, namely for the oxidative dehydrogenation of propane to propene. However, the control of both polymorphism (⍺- versus β-phase, the latter being metastable at RT but the most selective one for propene formation) and textural properties remains a challenge. The purpose of this presentation is to describe the developments we made during the last years in the frame of a new approach based on hybrid organic-inorganic precursors. NiMoO4 is here prepared through the thermal degradation in air of hybrid precursors in which inorganic ions ([Ni(H2O)6) 2+], MoO4 2-) are homogeneously dispersed in a polyampholytic copolymer, poly(N,Ndiallyl-N-alkylamine-alt-maleic acid), with a combination of electrostatic and complexation interactions. The latter matrix was shown previously to display a lamellar supramolecular organization governed by hydrophobic interactions between tuneable alkyl side chains of 6, 12 or 18 carbon atoms.
Rapid and early crystallization of NiMoO4 under mild (350-450°C) calcination conditions is induced by the highly exothermal decomposition of the matrix, avoiding undesired sintering. This process allows the stabilization of the β-NiMoO4 phase which is metastable at RT. Mesoporous NiMoO4 is obtained here, while classical preparation routes generate non-porous materials. The presence of pores and their lamellar shape are assigned to the supramolecular organization in the hybrid original matrix. Both the pore size and the specific surface area increase with the length of the side alkyl chains. This non-classical hybrid route provides NiMoO4 with features responsible for better catalytic performance in propane ODH when compared with non-porous catalysts obtained by co-precipitation.
Today’s photovoltaic sources are still dominated by the crystalline Si technology. However, the use of bulk Si is limited because of material consumption, competition with microelectronic industry for high-quality Si materials, efficiency limits and only limited output under low-light conditions (when the sky is overcast or indoors). Organic photovoltaics (OPV) with its variety of polymers suitable for light-harvesting, cheap fabrication, a flexibility of the modules and operation in the dim light conditions can be a promising alternative for silicon-based photovoltaics. Carbon materials (graphene and nanotubes) combination with organic polymers is regarded as a prospective active material in OPV and is currently being explored. However, the perspectives of nanodiamond (ND) in OPV, in spite of the unique properties of the material, remain unexplored. NDs and their structural as well as electronic properties are very stable under various conditions for a long time. Diamond nanoparticles are merely carbon and they are completely non-toxic. Covalent chemistry works similarly as for organics and thus they enable grafting of various chemical moieties on NDs surface. NDs are also available in large quantities at reasonable prices.
In this work composites of nanodiamond and polypyrrole (PPy) as organic dye were fabricated by inexpensive scalable technology and its opto-electronic properties were investigated. Infrared spectroscopy and atomic force microscopy evidence formation and pronounced mutual interaction of PPy and nanodiamond in the composite at the nanoscale. The nanocomposite exhibits the highest photovoltage and highly enhanced broadband (1- 3.5 eV) absorption coefficient compared to pristine materials. In this respect combination of both oxygen and hydrogen functional groups appears to be the most favorable surface termination of nanodiamond in its composite with PPy for light harvesting. Theoretical DFT calculations reveal HOMO and LUMO spatial separation at the nanodiamond-PPy interface and energetic level alignment favorable for exciton dissociation. Assembled preliminary hybrid solar cells with ND/PPy as an active material prove functionality of the concept with opportunity for further improvement. The results of the opto-electronic measurements open the prospects for a breakthrough in the field of organic photovoltaics. The work was supported by GACR 15-01809S and MSMT project CZ.02.1.01/0.0/0.0/15_003/0000464.
Sustainability is the edifice for the development of efficient chemical processes. Catalytic transformations are especially attractive owing to the generally mild and selective reaction conditions and the reduction of waste byproducts. Nevertheless, even catalysts need to be efficiently removed from a reaction mixture, often down to the ppm levels due to the toxicity of some transition metals that are being used. Magnetic nanoparticles are attractive platforms for catalysts and reagents, which can be rapidly and quantitatively removed with the aid of an external magnet. Choosing examples from our research group, strategies for covalent and non-covalent immobilization of catalysts, reagents, and functional materials on magnetic nanoparticles, as well as their application in various areas of organic synthesis, will be discussed.
Carbon based nanofillers have been of interest to researchers for decades. Carbon allotropes such as graphene have been embedded in various matrices to improve the material property such as gas-barrier, thermal-conductivity and tensile-strength of the parent material. One such material is bitumen, for the reason that nearly 70% of all global road is made of asphalt (bitumen + aggregate). Bitumen, as we know it, is a petroleum byproduct with complex chemistry, contains naturally occurring nanoparticles known as asphaltene. The chemistry of bitumen and the percentage of asphaltene can vary greatly depending on external and internal factors such as the source and method of bitumen extraction. This makes graphene embedded bitumen a complex ternary phase system. Within the framework of this paper, we focus on the phase stability and particle interaction between graphene and asphaltene in order to optimize the process of tailoring the microstructure of graphene embedded bitumen to improve the gas barrier and mechanical properties. We use characterization techniques such as rotational-rheometer, DSC, chemical titration and road engineering standards such as RTFOT and penetration-grade to study the critical-clustering-concentration, phase behavior and the impact of embedding graphene to manufacturing process of asphalt. Phase separation and agglomeration of dissimilar nanoparticles was observed when graphene embedded bitumen (1% vol) was subjected to RTFOT, increasing the change in viscosity by 12.21-14.65% when compared to 10.31% in std. bitumen. Hence this paper aspires to provide a brief look into tailoring of nanocomposites with dissimilar nanofillers and embedding nanofillers such as graphene into complex matrices.
The most common tasks, we encounter during restoration stone historical monument buildings, include mainly cleaning and removing of the crust from their surface. As part of the experimental research of nanomaterials and the widespread use of these materials for the preservation and restoration of stone monuments, the use of TiO2 is currently being addressed. Applications have shown that this oxide can be used to protect against microorganisms and UV degradation due to its antifungal and antibacterial effects. At the same time, the photocatalytic properties of TiO2 represent the possibility of chemical decomposition and the creation of a self-cleaning environment and self-sterilization area. Applying lime nanosuspensions with TiO2 nanoparticles will reduce the rate of deposition of pollutants as a result of photocatalytic phenomena and thus slow the development of degradation processes.
Most of the biofertilizers and biopesticides are of microbial and biochemical origin (bacteria, fungi, plant extracts). Though sustainable and environment-friendly shelf life of microbial inoculants, on-field stability, and active dosage remain critical issues.
A major reason is the fact that bacteria-loaded water-based biopolymer coatings are of low mechanical stability and are prone to increased permeability of small molecules like water vapor and oxygen including reactive oxygen species that dramatically reduce bacterial viability and functionality and furthermore shelf life of formulated seeds. Concerning spray formulations adhesion to the leaves, protection against sunlight (UV), wind and rain and precision of delivery (spraying pattern, spraying volume, time and frequency) are important issues.
Using nanocellulose as filler in microbial seed coatings and protective shell and adhesion promoter in spray formulations we aim to substantially improve stability and efficiency of microbial formulations. Different compositions of nanocellulose based composite liquid formulations were evaluated with respect to the viability of desiccation-sensitive Gram negative Paraburkholderia phytofirmans, PsJN and Pseudomonas putida, furthermore robust Gram positive spore-forming strains (Paenibacillus sp.). Typical binder materials include gelatine, whey protein, polyvinylpyrrolidone (PVP), poly vinyl alcohol (PVA) and carboxymethylcellulose (CMC) amongst others. Biocompatibility of the selected materials and desiccation tolerance of the selected bacteria were evaluated in screening tests. Effect of pH, concentration, viscosity and osmolarity on microbial viability was evaluated as well as UV absorbance, adhesion to plant leaves and spraying pattern were investigated. Results from field tests on maize and hortensia finally add to chemical and microscopic analysis of composite formulations and plant/microbe - nanocomposite interactions and highlight the potential of nanocellulose in agroformulations.