Search query: charge transport polymer

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abstract: Charge transport in conjugated polymer semiconductors has traditionally been thought to be limited to a low mobility regime by pronounced energetic disorder. Much progress has recently been made in advancing carrier mobilities in field effect transistors through developing low disorder conjugated polymers. However, in diodes these polymers have to date not shown much improved mobilities, presumably reflecting the fact that in diodes lower carrier concentrations are available to fill up residual tail states in the density of states. Here, we show that the bulk charge transport in low disorder polymers is limited by water induced trap states and that their concentration can be dramatically reduced through incorporating small molecular additives into the polymer film. Upon incorporation of the additives we achieve space charge limited current characteristics that resemble molecular single crystals such as rubrene with high, trap free SCLC mobilities up to 0.2 cm2/Vs and a width of the residual tail state distribution comparable to kBT.Charge transport in organic diodes based on conjugated polymers is severely limited by the high water related trap concentration and energetic disorder. Here, the authors report high mobility trap free charge transport in low disorder conjugated polymers by incorporating small molecular additives.
author_names: Mark Nikolka

Katharina Broch

John Armitage

David A Hanifi

Peer J Nowack

Deepak Venkateshvaran

Aditya Sadhanala

Jan Saska

Mark Mascal

Seok-Heon Jung

Jin-Kyun Lee

Iain McCulloch

Alberto Salleo

Henning Sirringhaus
title: High mobility, trap free charge transport in conjugated polymer diodes
venue: Nature Communications
year: 2019

abstract: Room temperature flexible heat harvesters based on conducting polymers are ideally suited to cover the energy demands of the modern nomadic society. The optimization of their thermoelectric efficiency is usually sought by tuning the oxidation levels of the conducting polymers, even if such methodology is detrimental to the Seebeck coefficient (S) as both the Seebeck coefficient and the electrical conductivity (s) are antagonistically related to the carrier concentration. Here we report a concurrent increase of S and s and we experimentally derive the dependence of Seebeck coefficient on charge carrier mobility for the first time in organic electronics. Through specific control of the conducting polymer synthesis, we enabled the formation of a denser percolation network that facilitated the charge transport and the thermodiffusion of the charge carriers inside the conducting polymer layer, while the material shifted from a Fermi glass towards a semi metal, as its crystallinity increased. This work sheds light upon the origin of the thermoelectric properties of conducting polymers, but also underlines the importance of enhanced charge carrier mobility for the design of efficient thermoelectric polymers.
author_names: Ioannis Petsagkourakis

Eleni Pavlopoulou

Eric Cloutet

Yan Chen

Xjianjie Liu

Mats Fahlman

Magnus Berggren

Xavier Crispin

Stefan Dilhaire

Guillaume Fleury

Georges Hadziioannou
title: Correlating the Seebeck coefficient of thermoelectric polymer thin films to their charge transport mechanism
year: 2018

abstract: Beating the heat by blending Charge carriers move through semiconductor polymers by hopping transport. In principle, these polymers should be more conductive at higher temperatures. In practice, conductivity drops at high temperatures because interchain contacts are disrupted, which limits potential applications. Gumyusenge et al. now show that appropriate blending of a semicrystalline conjugated polymer with an insulating polymer that has a high glass transition temperature creates a morphology that stabilizes a network of semiconductor channels. High charge conductivity was maintained in these materials up to 220degC. Science, this issue p. 1131 Polymer semiconductors can maintain their conductivity at high temperatures when blended into insulating host polymers. Although high temperature operation (i.e. beyond 150degC) is of great interest for many electronics applications, achieving stable carrier mobilities for organic semiconductors at elevated temperatures is fundamentally challenging. We report a general strategy to make thermally stable high temperature semiconducting polymer blends, composed of interpenetrating semicrystalline conjugated polymers and high glass transition temperature insulating matrices. When properly engineered, such polymer blends display a temperature insensitive charge transport behavior with hole mobility exceeding 2.0 cm2/V*s across a wide temperature range from room temperature up to 220degC in thin film transistors.
author_names: Aristide Gumyusenge

Dung Thuy Thi Tran

Xuyi Luo

Gregory Matthew Pitch

Yan Zhao

Kaelon A Jenkins

Tim J Dunn

Alexander L Ayzner

Brett M Savoie

Jianguo Mei
title: Semiconducting polymer blends that exhibit stable charge transport at high temperatures
venue: Science
year: 2018

abstract: Charge transport and film microstructure evolution are investigated in a series of polyethylenimine (PEI) doped (0.0 6.0 wt% amorphous metal oxide (MO) semiconductor thin film blends. Here, PEI doping generality is broadened from binary In2O3 to ternary (e.g. In+Zn in IZO, In+Ga in IGO) and quaternary (e.g. In+Zn+Ga in IGZO) systems, demonstrating the universality of this approach for polymer electron doping of MO matrices. Systematic comparison of the effects of various metal ions on the electronic transport and film microstructure of these blends are investigated by combined thin film transistor (TFT) response, AFM, XPS, XRD, X ray reflectivity, and cross sectional TEM. Morphological analysis reveals that layered MO film microstructures predominate in PEI In2O3, but become less distinct in IGO and are not detectable in IZO and IGZO. TFT charge transport measurements indicate a general coincidence of a peak in carrier mobility (mpeak) and overall TFT performance at optimal PEI doping concentrations. Optimal PEI loadings that yield mpeak values depend not only on the MO elemental composition but also, equally important, on the metal atomic ratios. By investigating the relationship between the MO energy levels and PEI doping by UPS, it is concluded that the efficiency of PEI electron donation is highly dependent on the metal oxide matrix work function in cases where film morphology is optimal, as in the IGO compositions. The results of this investigation demonstrate the broad generality and efficacy of PEI electron doping applied to electronically functional metal oxide systems and that the resulting film microstructure, morphology, and energy level modifications are all vital to understanding charge transport in these amorphous oxide blends.
author_names: Wei Huang

Peijun Guo

Li Zeng

Ran Li

Binghao Wang

Gang Wang

Xinan Zhang

R P H Chang

Junsheng Yu

Michael J Bedzyk

Tobin J Marks

Antonio F Facchetti
title: Metal Composition and Polyethylenimine Doping Capacity Effects on Semiconducting Metal Oxide Polymer Blend Charge Transport.
venue: Journal of the American Chemical Society
year: 2018

abstract: T.D.A. and A.F.P acknowledge financial support from Cambridge Display Technology (Company No. 2672530) O.S. acknowledges the support of the Center for Absorption in Science of the Ministry of Immigrant Absorption under the framework of the KAMEA Program.
author_names: Alexandra F Paterson

Yen-Hung Lin

Alexander D Mottram

Zhuping Fei

Muhammad Rizwan Niazi

Ahmad R Kirmani

Aram Amassian

Olga Solomeshch

Nir Tessler

Martin Heeney

Thomas D Anthopoulos
title: The Impact of Molecular p Doping on Charge Transport in High Mobility Small Molecule/Polymer Blend Organic Transistors
year: 2018

abstract: Significance Shear printing of electroactive polymers using natural brushes is a promising film deposition technique for printed electronics capable of microstructure control and electrical properties enhancement over large areas. Nevertheless, the interplay between film printing parameters, microstructure development, and charge transport is not well understood. We report that natural brush printing greatly enhances charge transport by as much as 5.7x through control of polymer nanofibril aggregate growth and backbone alignment, attributable to the oriented squamae of the natural hair. However, while brush shear induced aggregation enhances charge transport, we show that backbone alignment alone does not guarantee charge transport anisotropy. These results provide additional understanding of shear induced enhanced charge transport and set processing guidelines for high performance printed organic circuitry. Shear printing is a promising processing technique in organic electronics for microstructure/charge transport modification and large area film fabrication. Nevertheless, the mechanism by which shear printing can enhance charge transport is not well understood. In this study, a printing method using natural brushes is adopted as an informative tool to realize direct aggregation control of conjugated polymers and to investigate the interplay between printing parameters, macromolecule backbone alignment and aggregation, and charge transport anisotropy in a conjugated polymer series differing in architecture and electronic structure. This series includes (i) semicrystalline hole transporting P3HT, (ii) semicrystalline electron transporting N2200, (iii) low crystallinity hole transporting PBDTT FTTE, and (iv) low crystallinity conducting PEDOT:PSS. The (semi )conducting films are characterized by a battery of morphology and microstructure analysis techniques and by charge transport measurements. We report that remarkably enhanced mobilities/conductivities, as high as 5.7x/3.9x, are achieved by controlled growth of nanofibril aggregates and by backbone alignment, with the adjusted R2 (R2adj) correlation between aggregation and charge transport as high as 95% However, while shear induced aggregation is important for enhancing charge transport, backbone alignment alone does not guarantee charge transport anisotropy. The correlations between efficient charge transport and aggregation are clearly shown, while mobility and degree of orientation are not always well correlated. These observations provide insights into macroscopic charge transport mechanisms in conjugated polymers and suggest guidelines for optimization.
author_names: Gang Wang

Wei Huang

Nicholas D Eastham

Simone Fabiano

Eric F Manley

Li Zeng

Binghao Wang

Xinan Zhang

Zhihua Chen

Ran Li

R P H Chang

Lin X Chen

Michael J Bedzyk

Ferdinand S Melkonyan

Antonio F Facchetti

Tobin J Marks
title: Aggregation control in natural brush printed conjugated polymer films and implications for enhancing charge transport
venue: Proceedings of the National Academy of Sciences
year: 2017

abstract: Morphology of conjugated polymers is a critical factor that significantly affects intrinsic charge transport characteristics and in turn performance of polymer based devices. Morphological defects including misaligned crystalline grains and grain boundaries significantly impede efficient charge hopping between transport sites, resulting in degradation of device performance. Therefore, one important challenge is to control morphology of active polymer thin films for achieving high performance flexible electronic devices. In the past decade, significant progress has been achieved in morphology control of conjugated polymer thin films using solution based processing techniques. This review focuses on recent advances in processing strategies that can tune the morphologies and thus impact charge transport properties of conjugated polymer thin films. Of the available processing strategies, polymer solution treatments and film deposition techniques will be mainly highlighted. The correlation between processing conditions, active layer morphologies, and device performance will be also be discussed.
author_names: Mincheol Chang

Gyun-Taek Lim

Byoungnam Park

Elsa Reichmanis
title: Control of Molecular Ordering, Alignment, and Charge Transport in Solution Processed Conjugated Polymer Thin Films
venue: Polymers
year: 2017

abstract: Although the effects of alkyl chain spacers have been extensively studied for p type conjugated polymers with a donor (D) acceptor (A) repeating unit, few studies have examined their effects for n type polymers with an A D A architecture having two different acceptors in the repeating unit. Herein, diketopyrrolopyrrole thiophene bithiazole A D A type polymer semiconductors (DPPBTz) containing branched alkyl chains of 24 alkyl with C1 spacer (P 24 DPPBTz) and 29 alkyl with C6 spacer (P 29 DPPBTz) were designed and synthesized to elucidate the effect of the alkyl chain branching position on the electron dominant charge transport system. Due to the strong electron deficiency and trans planar conformation of the bithiazole group, DPPBTz based polymer semiconductors exhibit n type dominant electrical properties with a high electron mobility of up to 1.87 cm2 V 1 s 1. Systematic studies on the photophysical properties, thin film microstructures, and electrical properties of the DPPBTz polymers revealed that upon modification of the branching position, A D A n type dominant semiconductors differently behave compared to D A p type dominant semiconductors. This is attributed to the relatively weaker intermolecular interactions in A D A type semiconductors, making the C1 spacer more efficient for electron transport. These findings reveal the molecular design rule of alkyl side chains in A D A n type dominant conjugated polymers for the first time.
author_names: Hojeong Yu

Hyong Nam Kim

Inho Song

Yeon Hee Ha

Hyungju Ahn

Joon Hak Oh

Yun-Hi Kim
title: Effect of alkyl chain spacer on charge transport in n type dominant polymer semiconductors with a diketopyrrolopyrrole thiophene bithiazole acceptor donor acceptor unit
year: 2017

abstract: Abstract A metal free photoanode nanojunction architecture, composed of B doped carbon nitride nanolayer and bulk carbon nitride, was fabricated by a one step approach. This type of nanojunction (s BCN) overcomes a few intrinsic drawbacks of carbon nitride film (severe bulk charge recombination and slow charge transfer) The top layer of the nanojunction has a depth of ca. 100 nm and the bottom layer is ca. 900 nm. The nanojunction photoanode results into a 10 fold higher photocurrent than bulk graphitic carbon nitride (G CN) photoanode, with a record photocurrent density of 103.2 mA cm 2 at 1.23 V vs. RHE under one sun irradiation and an extremely high incident photon to current efficiency (IPCE) of ca. 10 at 400 nm. Electrochemical impedance spectroscopy, Mott Schottky plots, and intensity modulated photocurrent spectroscopy show that such enhancement is mainly due to the mitigated deep trap states, a more than 10 times faster charge transfer rate and nearly three times higher conductivity due to the nanojunction architecture.
author_names: Qiushi Ruan

Wenjun Luo

Jijia Xie

Yiou Wang

Xu Liu

Zhiming Bai

Claire J Carmalt

Junwang Tang
title: A Nanojunction Polymer Photoelectrode for Efficient Charge Transport and Separation
venue: Angewandte Chemie
year: 2017

abstract: The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce 2,3,5,6 tetrafluoro 7,7,8,8 tetracyanoquinodimethane (F4TCNQ) into poly(3 hexylthiophene 2,5 diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X ray data suggest that F4TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not p stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6 8 A from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F4TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm2 V 1 s 1 in the most crystalline P3HT samples. Temperature dependent conductivity measurements show that polaron mobility in SqP doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature.
author_names: D Tyler Scholes

Patrick Y Yee

Jeffrey R Lindemuth

Hyeyeon Kang

Jonathan W Onorato

Raja Ghosh

Christine K Luscombe

Frank C Spano

Sarah H Tolbert

Benjamin J Schwartz
title: The Effects of Crystallinity on Charge Transport and the Structure of Sequentially Processed F4TCNQ Doped Conjugated Polymer Films
year: 2017