Thickness threshold of structural ordering in thin MEH-PPV films

The microstructure of thin poly-[2-methoxy-5-(2′-ethyl-hexyloxy)-p- phenylene vinylene] (MEH-PPV) films was investigated by photoluminescence measurements and X-Ray diffraction analysis over thickness from several tens up to several hundreds of nanometer. Obtained results were correlated with exciton diffusion length obtained by the photovoltage method. All measurements revealed that there is a threshold thickness for the microstructural order as well as for exciton diffusion length which are primary physical properties for function of any device made up from such films. Development of more ordered phase can be observed above the critical thickness of about 150 nm. Below the threshold, the polymer chains are preferentially in conformations promoting localized intrachain interactions. Above the threshold, two main features can be observed: (i) the conjugation length of polymer chain segments reaches its maximum and (ii) polymer stacking in more ordered and larger crystalline domains influences strongly the material properties, namely enhances the exciton diffusion length. © 2014 Elsevier Ltd. All rights reserved.Operational Programme 'Education for Competitiveness'; European Social Fund (ESF); national budget of the Czech Republic [CZ.1.07/2.3.00/20.0104, CZ.1.05/2.1.00/03.0111]; Operational Programme 'Research and Development for Innovations'; European Regional Development Fund (ERDF

Thickness threshold of structural ordering in thin MEH-PPV films

The microstructure of thin poly-[2-methoxy-5-(2′-ethyl-hexyloxy)-p- phenylene vinylene] (MEH-PPV) films was investigated by photoluminescence measurements and X-Ray diffraction analysis over thickness from several tens up to several hundreds of nanometer. Obtained results were correlated with exciton diffusion length obtained by the photovoltage method. All measurements revealed that there is a threshold thickness for the microstructural order as well as for exciton diffusion length which are primary physical properties for function of any device made up from such films. Development of more ordered phase can be observed above the critical thickness of about 150 nm. Below the threshold, the polymer chains are preferentially in conformations promoting localized intrachain interactions. Above the threshold, two main features can be observed: (i) the conjugation length of polymer chain segments reaches its maximum and (ii) polymer stacking in more ordered and larger crystalline domains influences strongly the material properties, namely enhances the exciton diffusion length. © 2014 Elsevier Ltd. All rights reserved.Operational Programme 'Education for Competitiveness'; European Social Fund (ESF); national budget of the Czech Republic [CZ.1.07/2.3.00/20.0104, CZ.1.05/2.1.00/03.0111]; Operational Programme 'Research and Development for Innovations'; European Regional Development Fund (ERDF

Exciton diffusion length and concentration of holes in MEH-PPV polymer using the surface voltage and surface photovoltage methods

Novelized method of the surface photovoltage (SPV) measurement convenient for evaluation of exciton diffusion length and thickness of the space charge region (SCR) in organic semiconductors is applied to poly[2-methoxy-5-(2′- ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) polymer. Exciton diffusion length and thickness of the SCR was found. The experiment is complemented by measurements of surface potential by the Kelvin probe force microscopy yielding the work function and concentration of free holes. The latter value is much lower than the concentration of ionized states determined from the thickness of the space charge region, which can be ascribed to the presence of traps. © 2012 Elsevier B.V. All rights reserved

Charge transient, electrochemical and impedance measurements as tools for characterization of nano-heterostructural organic/inorganic semiconductors

Some organic small molecules as well as conjugated polymers are attractive organic semiconductors with rich applications in the branch of immerging organic electronics, e.g., in light-emitting, switching and photovoltaic devices. Surprisingly, there is the lack of methods, suitable for elucidation of basic injection and transport properties. This contribution deals with application of several techniques based on charge transient measurements, isothermal charge transient spectroscopy (IQTS) in microscopic mode, electrochemical methods of double step voltcoulometry (DSVCM) and electrochemical impedance spectroscopy (EIS), which are potentially suitable for obtaining information about basic parameters of traps and their influence on the transport properties. To test the characterization methods we first used the prototypical polysilane-poly[methyl(phenyl)silylene] (PMPSi). Phototodegradation of the by UV radiation is known to cause chain scission and creation of dangling bonds and weak bonds by known mechanisms. Next we show the applicability to study the electron structure of presented methods on PPV and blend of PPV and nano-CdS

Trade-off between high performance and long life due to nanofiller effects in polymer LEDs: MEH-PPV/Al2O3 nanocomposite study

This work presents the effect of nanofiller (Al2O3) in the polymer matrix MEH-PPV - Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] on optical, optoelectronic, and electrical properties. These properties were investigated using UV–Vis absorption, and photoluminescence spectroscopy. Exciton diffusion length was examined using the surface photovoltage (SPV) method, mobility of charge carriers was evaluated with charge extraction by linearly increasing voltage (CELIV) measurements. Information concerning the band structure was obtained using energy resolved-electrochemical impedance spectroscopy (ER-EIS). The influence of nanoparticles on the development of the micro structure in thin layers was examine with grazing-incidence wide-angle X-ray scattering (GIWAXS). Prepared nanocomposite thin films were subsequently used as active layers in polymer light-emitting diodes. Luminance, current efficiency, and stability of prepared polymer light emitting diodes were tested. The presented work clarifies the effect of non-conductive nanofiller on the properties of the polymer matrix and on the performance of OLEDs with an active layer made of nanocomposite material.DKRVO, (RP/CPS/2022/007); Internal Grant Agency of Tomas Bata University, (IGA/CPS/2023/006, IGA/CPS/2024/002); Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Agentúra na Podporu Výskumu a Vývoja, APVV, (APVV-22-0132); Vedecká Grantová Agentúra MŠVVaŠ SR a SAV, VEGA, (2/0165/22)Ministry of Education, Youth and Sports of the Czech Republic [RP/CPS/2022/007]; Internal Grant Agency of Tomas Bata University in Zln [IGA/CPS/2023/006, IGA/CPS/2024/002]; Slovak Scientific Grant Agency VEGA [2/0165/22]; Slovak Research and Development Agency [APVV-22-0132

An experimental and theoretical study of the structural ordering of the PTB7 polymer at a mesoscopic scale

Our extensive study based on optoelectronic and electric measurements (which consisted of: UV–Vis absorption, photoluminescence, surface photovoltage measurement, charge extraction by linearly increasing voltage, and energy-resolved electrochemical impedance spectroscopy) revealed the fundamental role of the thickness of the formation of intra- and interchain interaction in poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) films. We have shown that the final optoelectronic and electronic properties of PTB7 films are governed by the structural ordering development of the transition from nano-to submicroscale. The ordering of polymer chains and competition between the formation of J- and H-aggregates results in a non-trivial dependence of luminescence, exciton diffusion length, transport band gap, and defect concentration. According to a theoretical analysis, the driving forces responsible for the observed phenomena are associated with the thickness threshold dependence of the thin film drying mode which can proceed with or without the polymer skin formation on the surface of forming film. © 2019 Elsevier LtdMinistry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504]; Operational Program Research and Development for Innovations - European Regional Development Fund (ERDF); national budget of the Czech Republic [CZ.1.05/2.1.00/19.0409]; Internal Grant Agency of TBU [IGA/CPS/2016/007, IGA/CPS/2017/008, IGA/CPS/2018/007]; Scientific Grant Agency VEGA [2/0081/18]; Slovak Research and Development Agency [APVV SK-CN-RD-18-0006]; [SVV 260 444/2018