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Intrinsic Organic Semiconductors as Hole Transport Layers in p–i–n Perovskite Solar Cells
No full textThin polymeric and small-molecular-weight organic semiconductors are widely
employed as hole transport layers (HTLs) in perovskite solar cells. To ensure
ohmic contact with the electrodes, the use of doping or additional high work
function (WF) interlayer is common. In some cases, however, intrinsic organic
semiconductors can be used without any additive or buffer layers, although their
thickness must be tuned to ensure selective and ohmic hole transport. Herein,
the characteristics of thin HTLs in vacuum-deposited perovskite solar cells are
studied, and it is found that only very thin (<5 nm) HTLs readily result in
high-performing devices, as the HTL acts as a WF enhancer while still ensuring
selective hole transfer, as suggested by ultraviolet photoemission spectroscopy
and Kelvin probe measurements. For thicker films (≥5 nm), a dynamic behavior
for consecutive electrical measurements is observed, a phenomenon which is
also common to other widely used HTLs. Finally, it is found that despite their
glass transition temperature, small-molecule HTLs lead to thermally unstable
solar cells, as opposed to polymeric materials. The origin of the degradation
is still not clear, but might be related to chemical reactions/diffusion at the
HTL/perovskite interface, in detriment of the device stability
Vacuum-deposited Multi-Cation Wide Bandgap Perovskite Solar Cells
No full textMetal halide perovskites have proven to be excellent semiconductors, with tunable band gap, high
absorption coefficients and large charge diffusion length. Multi-component lead halide perovskite
compositions are widely studied in order to stabilize the perovskite phase, in particular for wide bandgap
formulations. The vacuum-deposition of multi-component perovskites is not straightforward, as the number
of precursors is in principle limited by the number of thermal sources available in the vacuum chamber.
Here we present a process which allows to increase the complexity of the formulation of vacuum-deposited
lead halide perovskites films by multi-source deposition and pre-mixing both inorganic and organic
components. We apply it to the preparation of wide bandgap CsMAFA triple-cation perovskite solar cells,
which are found to be efficient but not thermally stable. With the aim of stabilizing the perovskite phase,
we add guanidinium (GA+) to the material formulation, and obtained CsMAFAGA quadruple-cation
perovskite films with improved thermal stability, as observed by X-ray diffraction and rationalized by
microstructural analysis. The corresponding solar cells showed similar performance with a remarkable
thermal stability, when compared to the triple-cation perovskite devices. This work paves the way towards
the vacuum-processing of complex perovskite formulations, with important implications not only for
photovoltaics but also for other fields of application
Mehanizmi adsorpcije jona Mn2+ u strukturu kompozita na bazi cementa i mineralnih aditiva
No full textPrirodni zeolit i bentonit korišćeni su kao mineralni aditivi za pripremu građevinskih kompozita na bazi cementa bezbednih za životnu sredinu. Ovo istraživanje se fokusira na adsorpcione kvalitete i mehanizme ove dve glinene sirovine, odnosno njihovu sklonost ka imobilizaciji jona teških metala poput Mn2+. Dobijeni rezultati su ispitani korišćenjem kinetičkih modela pseudo-prvog i pseudo-drugog reda. Ispitane su Langmirove i Frojndlihove izoterme. Zeolit i bentonit imaju različite adsorpcione afinitete za Mn2+ katjone. Sedam cementnih kompozita sa različitim mineralnim dodacima (leteći pepeo, zeolit, bentonit) podvrgnuto je ispitivanju luženja. Mehanizmi adsorpcije i hidratacije koji su imobilisali teške metale unutar cementnih kompozita doveli su do toga da eluati dobijeni na uzorcima cementa sa dodatkom letećeg pepela i gline (zeolit ili bentonit) sadrže niže koncentracije Mn2+ jona od procednih voda dobijenih na uzorcima cementa sa elektrofilterskim pepelom
Our MoDeCo2000: Results Overview of the Scientific and Research Project
No full textProject Mortar Design for Conservation - Danube Roman Frontier 2000 Years after (MoDeCo2000) deals with mortars used from the 1st to the 6th century AD along the part of the Danube frontier that is situated in the territory of today's Serbia and whose monuments form the UNESCO tentative list “Frontier of the Roman Empire - Danube Limes in Serbia”. The mentioned territory was a provincial area in the Roman period, and the construction activities that happened in this part of the empire were not particularly interesting to the international scientific community dealing with Roman architecture. The aim of this project is to gain knowledge of ancient mortar technology in this area, to allow conclusions to be made about building activities, the exploitation and use of raw materials, as well as the everyday life of the people on the frontier. After interpreting the results obtained in laboratories of testing historical materials, the project is making compatible mixtures of mortars for the future conservation of the Limes monuments, using local raw materials, but also improving the properties of these mortars with different additions
Design of Compatible Mortars for Conservation Interventions
No full textArchitectural heritage suffers from many deterioration patterns among which mortar aging and degradation present a significant task for conservation practitioners and scientists. The functional requirements of compatible repair mortars strongly depend on the properties of historical mortars. In this sense, in depth characterisation of historical mortars and technologies is crucial for the development and design of the repair mortars
Narrowband Monolithic Perovskite–Perovskite Tandem Photodetectors
No full textNarrowband photodetectors (PDs) are sought after for many applications
requiring selective spectral response. The most common systems combine
optical bandpass filters with broadband photodiodes. This work reports a
method to obtain a narrowband response in a perovskite PD by the monolithic
integration of a perovskite photoconductor and a perovskite photodiode.
The spectral response of the tandem PD is determined by the bandgap
energy difference of the two perovskites, and exhibits a full width at half
maximum below 85 nm, an external quantum efficiency up to 68% and a high
specific detectivity of ≈1012 Jones in reverse bias, enabling the device to detect
weak light signals. The absorption profile of the narrowband PD can be tuned
by changing the thickness and bandgap of the wide bandgap perovskite
absorber
Aplitic Granite Waste as Raw Material for the Production of Outdoor Ceramic Floor Tiles
Get PDFOne of the significant problems in the production of ceramic tiles is the very high consump-tion of natural resources such as clay, feldspar, and quartz. The possibility of replacing part of the formulation of ceramic batches is of great importance. In this research, the possibility of using aplitic granite waste from dimensional stone production was analyzed in detail. The waste is considered a low-cost substitute for feldspar in Serbia. The milled powdery waste was analytically tested to reveal its chemical and mineralogical contents, particle size distribution, and other important properties. The ceramic tiles containing aplitic granite waste (GW) and GW/raw clay mixture (CGW) were hydraulically pressed, and the ceramic and technological properties determined. This waste can act as a filler while forming, drying, and firing, since the high content of quartz helps to control the shrinkage and acts as a fluxing agent in high temperatures due to its feldspathic nature. The waste was found favorable in the production of ceramic tiles, as the gained values of modulus of rupture and water absorption were 28.68 MPa and 1.33%, respectively. The parameters defined in the series of standards EN ISO 10545 were tested on a semi-industrial probe, determining that this combination of materials (without the addition of quartz) may be efficiently used to produce ceramic floor tiles. The usage of what would otherwise be waste material contributes to sustainable management and environmentally friendly solutions by avoiding landfilling, while at the same time it enabling the conservation of scarce natural feldspar deposits
Failure analysis of beam of unmanned aerial vehicle
No full textThe high level of worthiness of unmanned aerial vehicles (UAV), particularly in everyday life, is something that will be common thing in close future. The design solutions for UAV us subject of constant innovation, focused on the improving structure performances and weight reducing. The use of new materials. like various composites, is necessary during this process to fulfill such demanding structural design requirements. Despite the fact that such kind of composite made UAV structures are subjected to the detailed calculation procedures and experimental verifications in the design phase, the fracture and failure can occur during testing in real operation conditions. The redesign procedure is required in order to overcome the noted issues.
This paper describes failure analysis, as well as structural redesign procedure for a beam element of an unconventional UAV. The fracture analysis is based on the numerical calculations of the deformation and stress state of the element, as well as experimental investigation of material characteristics. The developed redesign solution contains modifications in material of the element, as well as the changes in the structure design of the failure zone. The Finite Element Analysis is performed and discussed for both of the element structures: original design and redesign based on the fracture analysis. The conclusions obtained by the comparison of these Finite Element Analyses show the significant structure improvements in the stress concentration zone, achieved by the proposed redesign
