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    Density of bulk trap states of hybrid lead halide perovskite single crystals: temperature modulated space-charge-limited-currents
    (Springer Nature, 2019-03-04) Pospíšil, Jan; Zmeškal, Oldřich; Nešpůrek, Stanislav; Krajčovič, Jozef; Weiter, Martin; Kovalenko, Alexander
    Temperature-modulated space-charge-limited-current spectroscopy (TMSCLC) is applied to quantitatively evaluate the density of trap states in the band-gap with high energy resolution of semiconducting hybrid lead halide perovskite single crystals. Interestingly multicomponent deep trap states were observed in the pure perovskite crystals, which assumingly caused by the formation of nanodomains due to the presence of the mobile species in the perovskites.
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    Study of Optical and Electrical Properties of Organic Thin Films for Photovoltaic Applications
    (Kaunas University of Technology, 2015-09-02) Pospíšil, Jan; Schmiedová, Veronika; Zmeškal, Oldřich; Černý, Jiří
    The paper deals with the study of optical, electrical and dielectric properties of thin film organic materials suitable for the preparation of optoelectronic devices (e.g. photodiodes, phototransistors, photovoltaic cells). As active layers palladium phthalocyanine (PdPc[t-Bu]4), fullerene (acceptor material, PCBM) and their mixture (9:5 mass %) were used. Thin films were prepared by two methods: by spin coating (Chemat technology Spin Coater) and by material inkjet printing (Dimatix Materials Printer DMP-2800). UV-VIS spectroscopy and ellipsometry were used to study the optical properties. The paper also presents results of electrical and dielectric measurements.
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    Vacuum Deposited Diphenyl-Diketo-Pyrrolopyrroles Structures with Photoelectrical Application
    (IOP Publishing Ltd, 2014-05-15) Georgiev, Yavor; Zhivkov, Ivaylo; Angelov, George; Takov, Tihomir; Přikryl, Radek; Stříteský, Stanislav; Vrchotová, Jana; Weiter, Martin
    ITO|composite|Al structures with active DPP-C60 composite films (ratio 60:40 mass %) of about 100 nm thicknesses were prepared. The surface morphology of the films was studied by SEM imaging, which revealed uniform films containing separate spherical structures. It was found that the optimized preparation of the structures under the aforementioned conditions leads to an improvement of their photoelectrical properties.
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    An Electrochemical NO2 Sensor Based on Ionic Liquid: Influence of the Morphology of the Polymer Electrolyte on Sensor Sensitivity
    (MDPI, 2015-11-11) Kuberský, Petr; Altšmíd, Jakub; Hamáček, Aleš; Nešpůrek, Stanislav; Zmeškal, Oldřich
    A systematic study was carried out to investigate the effect of ionic liquid in solid polymer electrolyte (SPE) and its layer morphology on the characteristics of an electrochemical amperometric nitrogen dioxide sensor. Five different ionic liquids were immobilized into a solid polymer electrolyte and key sensor parameters (sensitivity, response/recovery times, hysteresis and limit of detection) were characterized. The study revealed that the sensor based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][N(Tf)2]) showed the best sensitivity, fast response/recovery times, and low sensor response hysteresis. The working electrode, deposited from water-based carbon nanotube ink, was prepared by aerosol-jet printing technology. It was observed that the thermal treatment and crystallinity of poly(vinylidene fluoride) (PVDF) in the solid polymer electrolyte influenced the sensitivity. Picture analysis of the morphology of the SPE layer based on [EMIM][N(Tf)2] ionic liquid treated under different conditions suggests that the sensor sensitivity strongly depends on the fractal dimension of PVDF spherical objects in SPE. Their deformation, e.g., due to crowding, leads to a decrease in sensor sensitivity.
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    Physical properties investigation of reduced graphene oxide thin films prepared by material inkjet printing
    (Hindawi Publishing Corporation, 2017-08-23) Schmiedová, Veronika; Pospíšil, Jan; Kovalenko, Alexander; Čuboň, Tomáš; Zmeškal, Oldřich; Weiter, Martin
    The article is focused on the study of the optical properties of inkjet-printed graphene oxide (GO) layers by spectroscopic ellipsometry. Due to its unique optical and electrical properties, GO can be used as, for example, a transparent and flexible electrode material in organic and printed electronics. Spectroscopic ellipsometry was used to characterize the optical response of the GO layer and its reduced form (rGO, obtainable, for example, by reduction of prepared layers by either annealing, UV radiation, or chemical reduction) in the visible range. The thicknesses of the layers were determined by a mechanical profilometer and used as an input parameter for optical modeling. Ellipsometric spectra were analyzed according to the dispersion model and the influence of the reduction of GO on optical constants is discussed. Thus, detailed analysis of the ellipsometric data provides a unique tool for qualitative and also quantitative description of the optical properties of GO thin films for electronic applications.