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    Morphology versus Vertical Phase Segregation in Solvent Annealed Small Molecule Bulk Heterojunction Organic Solar Cells
    (Hindawi, 2015-10-11) Kovalenko, Alexander; Pospíšil, Jan; Zhivkov, Ivaylo; Vala, Martin; Weiter, Martin
    The deep study of solvent annealed small molecules bulk heterojunction organic solar cells based on DPP(TBFu)2 : PC60BM blend is carried out. To reveal the reason of the solvent annealing advantage over the thermal one, capacitance-voltage measurements were applied. It was found that controlling the vertical phase segregation in the solar cells a high fullerene population in the vicinity of the cathode could be achieved. This results in increase of the shunt resistance of the cell, thus improving the light harvesting efficiency.
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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.
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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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    Effect of the Side Chains and Anode Material on Thermal Stability and Performance of Bulk-Heterojunction Solar Cells Using DPP(TBFu) 2 Derivatives as Donor Materials
    (Hindawi, 2015-12-08) Kovalenko, Alexander; Vrchotová, Jana; Vala, Martin; Luňák, Stanislav; Weiter, Martin
    An optimized fabrication of bulk-heterojunction solar cells (BHJ SCs) based on previously reported diketopyrrolopyrrole donor,ethyl-hexylated DPP(TBFu)2,aswellastwonewDPP(TBFu)2derivatives with ethyl-hexyl acetate and diethyl acetal solubilizingside-chains and PC60BM as an acceptor is demonstrated. Slow gradual annealing of the solar cell causing the effective donor-acceptor reorganization, and as a result higher power conversion efficiency (PCE), is described. By replacing a hole transportinglayer PEDOT:PSS with MoO3we obtained higher PCE values as well as higher thermal stability of the anode contact interface.DPP(TBFu)2derivative containing ethyl-hexyl acetate solubilizing side-chains possessed the best as-cast self-assembly and highcrystallinity. However, the presence of ethyl-hexyl acetate and diethyl acetal electrophilic side-chains stabilizes HOMO energy ofisolated DPP(TBFu)2donors with respect to the ethyl-hexylated one, according to cyclic voltammetry. Effect of the Side Chains and Anode Material on Thermal Stability and Performance of Bulk-Heterojunction Solar Cells Using DPP(TBFu) 2 Derivatives as Donor Materials.
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    Organic Electrochemical Transistor Microplate for Real-Time Cell Culture Monitoring
    (MDPI, 2017-09-27) Salyk, Ota; Víteček, Jan; Omasta, Lukáš; Šafaříková, Eva; Stříteský, Stanislav; Vala, Martin; Weiter, Martin
    A microplate with a multielectrode array of 96 organic electrochemical transistors (OECTs) based on the semiconductive polymer poly(3,4-ethylenedioxythio-phene):poly(styrene sulfonic acid) PEDOT:PSS was developed and fabricated by the screen printing method. It consists of a microplate of a 12 × 8 chimney–well array with transistors on the bottom. The OECT is circular with a channel of 1.5 mm2 in the centre surrounded by the circular gate electrode.