Photophysical properties of halide perovskite CsPb(Br1-xIx)3 thin films and nanowires

This is an accepted manuscript of an article published by Elsevier in Journal of Luminescence on 26/12/2019, available online: https://doi.org/10.1016/j.jlumin.2019.116985 The accepted version of the publication may differ from the final published version.© 2019 Thin films and nanowires based on lead halide perovskites are promising objects for the design of various optoelectronic devices as well as nano- and microlasers. One of the main advantages of such materials is their absorption and photoluminescence spectra tuning across the visible range via the change in their chemical composition, for instance, by substitution of one halide atom (Br) for another one (I) in the crystal lattice of CsPb(Br1-xIx)3. However, this approach gives materials showing unstable photoluminescence behavior caused by light-induced perovskite phase separation under high-intensity excitation at room temperature. In this work, CsPb(Br1-xIx)3 thin films and nanowires are obtained by chemical vapor anion exchange method from their CsPbBr3 counterparts fabricated by improved wet chemical methods. Spontaneous and stimulated emission from the mixed-halide and pristine bromide samples are studied. Tribromide nanowires exhibit lasing with relatively low thresholds (10–100 μJ/cm2) and high Q-factor of the laser mode up to 3500. The temperature dependence of the photoinitiated phase separation in CsPbBr1.5I1.5 samples is investigated, showing that light-induced phase instability of the mixed-halide nanowires can be suppressed at the somewhat higher temperature (250 K) than the value observed for the thin films having a similar chemical composition. The results obtained are important for the optimization of the functioning of optoelectronic devices based on considered perovskite materials.S.V.M. and A.A.Z. thank the Russian Science Foundation (grant 17-73-20336) for the financial support of study of nanostructures. S.V.M. acknowledges funding from the Ministry of Science and Higher Education of the Russian Federation (project 14.Y26.31.0010). M.V. acknowledges funding from the European Regional Development Fund according to the supported activity ‘Research Projects Implemented by World-class Researcher Groups’ under Measure No. 01.2.2-LMT-K-718, grant No. 01.2.2-LMT-K-718-01-0014. G.H. acknowledges ITMO Fellowship Program.Accepted versio

Fabrication of high-mobility poly(3-hexylthiophene) transistors at ambient conditions

We report on the fabrication of high-mobility organic thin-film transistors (OTFTs) made and tested under ambient conditions. A bottom gate, bottom contact architecture was used with a layer of poly(3-hexylthiophene) deposited on a 50 nm thick Al2O3 dielectric with pre-patterned Au source and drain electrodes. Fluoroalkyl trichlorosilane treatment of the Al 2O3 dielectric was found to significantly improve device performance. The field-effect hole mobility reproducibly reached 0.2 cm 2 V-1 s-1 (best device 0.29 cm2 V-1 s-1) with an on/off ratio of 104. Electrical and synchrotron X-ray scattering characterization shows that an interaction at the FOTS/P3HT interface is responsible for the high performance of these devices. The fabrication method described here is carried out under ambient conditions and does not require any post-deposition annealing or vacuum drying steps for the organic film; therefore it can simplify the manufacturing of OTFTs. © 2010 Elsevier B.V. All rights reserved

A light-emitting memristor

A light-emitting memristor (LEM) is reported based on a metal/mixed conductor/metal structure, where the mixed conductor is the ionic transition metal complex ruthenium(II) tris(bipyridine) with hexafluorophosphate counter ions. The device shows memory effects upon the application of an ac bias, in both current and electroluminescence intensity. The observation of memory in light emission offers the potential for optical read-out of the state of memristive devices. © 2009 Elsevier B.V. All rights reserved

Structural phase transition in pentacene caused by molecular doping and its effect on charge carrier mobility

The structural properties and charge carrier mobility of pentacene doped by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and 2,2-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (F6-TCNNQ) are studied by X-ray diffraction, scanning electron microscopy, field effect transistor measurements, and space charge limited currents (SCLC). We observe the presence of polycrystalline and amorphous domains within the doped pentacene film grown under co-deposition conditions. The appearance of the amorphous phase is induced by the molecular dopants F4-TCNQ and F6-TCNNQ. A strong drop of crystallite size is obtained at a doping concentration of around 7 and 4 wt.%, respectively. The loss of the polycrystalline structure is correlated to a strong decrease of the charge carrier mobility in pentacene in horizontal and vertical film structures. We discuss typical scenarios of charge transport for polycrystalline and amorphous thin films in order to explain the observed loss of mobility originated by the doping induced structural phase transition. In this way an optimum doping concentration for highest conductivity with acceptable mobility is determined which can help to improve the performance of organic solar cells and organic high-frequency rectification diodes. © 2011 Elsevier B.V. All rights reserved

Molecular doping for control of gate bias stress in organic thin film transistors

The key active devices of future organic electronic circuits are organic thin film transistors (OTFTs). Reliability of OTFTs remains one of the most challenging obstacles to be overcome for broad commercial applications. In particular, bias stress was identified as the key instability under operation for numerous OTFT devices and interfaces. Despite a multitude of experimental observations, a comprehensive mechanism describing this behavior is still missing. Furthermore, controlled methods to overcome these instabilities are so far lacking. Here, we present the approach to control and significantly alleviate the bias stress effect by using molecular doping at low concentrations. For pentacene and silicon oxide as gate oxide, we are able to reduce the time constant of degradation by three orders of magnitude. The effect of molecular doping on the bias stress behavior is explained in terms of the shift of Fermi Level and, thus, exponentially reduced proton generation at the pentacene/oxide interface. © 2014 AIP Publishing LLC

High voltage polymer solar cell patterned with photolithography

An acid-sensitive semiperfluoroalkyl resorcinarene has recently been demonstrated as an effective photoresist for the photolithographic patterning of organic semiconductor materials. In this work, we show that it can be used to pattern polymer solar cells fabricated from a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), so as to obtain high open circuit voltages (Voc). An array of 300 solar cells in series, with a period of 50 m, achieved a Voc of 90 V and a power conversion efficiency (PCE) of 0.3%. © 2009 The Royal Society of Chemistry