Charge injection and transport in electrochemical films of poly(3-hexylthiophene)

Valaski, R.; Moreira, L. M.; Micaroni, Liliana; Hümmelgen, Ivo A.

doi:10.1063/1.1494850

Cited by 40 publications

(26 citation statements)

References 29 publications

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“…[4][5][6] The increase in mobility was related to side-chain-induced self-organization into a well-ordered twodimensional lamellar structure. 2 In contrast, electron transport has not been reported up to now in P3HT, most probably because electrons are heavily trapped. Molecular oxygen impurities have been proposed as one possible trap, 7 but little has been done to systematically address the issue.…”

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confidence: 95%

“…We report here a study that reveals unexpected promise for poly(3-hexylthiophene) (P3HT) as a material with both good electron and hole transport. P3HT has been widely studied in the past and is well known as being an effective hole transport polymer, with higher hole mobility than many other conjugated polymers, including the poly(phenylenevinylene)s. 2 Initially, however, rather low hole mobilities were reported for regiorandom P3HT. 3 However, when head-to-tail regioregularly substituted P3HT became available, the hole mobilities were found to be dramatically improved.…”

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confidence: 99%

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High ambipolar and balanced carrier mobility in regioregular poly(3-hexylthiophene)

Choulis

Kim

Nelson

et al. 2004

Applied Physics Letters

207

120

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The carrier transport of carefully purified regioregular poly(3-hexylthiophene) films has been studied using time-of-flight photocurrent measurements. We find balanced ambipolar transport with a room-temperature mobility for holes of 3 Ã 10 −4 cm 2 V −1 s −1 and for electrons of 1.5Ã 10 −4 cm 2 V −1 s −1 at electric fields ജ10 5 V / cm. The transport is relatively field independent and weakly temperature dependent, pointing to a high degree of chemical regioregularity and purity. Conjugated polymers are of increasing interest as new materials for electronic applications, offering the potential for low fabrication cost, easy processing, and flexibility. Organic light-emitting diodes (OLEDs), field-effect transistors (FETs), photodiodes, and solar cells are all applications under intense study and first products are already emerging. One of the limitations for the utilization of such organic semiconductors is that they have relatively poor carrier transport properties in terms both of absolute mobility and with respect to the balance between hole and electron mobility. Low mobilities can limit practical applications, for instance, of OLEDs in passive matrix addressed displays due to low current densities in the space-charge-limited current regime, and unbalanced transport can reduce OLED-based display emission efficiency. Low mobility also impacts on switching speed in FETs and on solar cell efficiency, and again unbalanced transport has additional drawbacks in both of these applications.In general, electron transport in conjugated polymers is much worse than hole transport, and tends to be highly dispersive, with no clear transit time observed in time-offlight (ToF) photocurrent measurements. 1 Better electron transport polymers are, therefore, much needed in order to achieve the desired combination of enhanced and balanced carrier transport. We report here a study that reveals unexpected promise for poly(3-hexylthiophene) (P3HT) as a material with both good electron and hole transport. P3HT has been widely studied in the past and is well known as being an effective hole transport polymer, with higher hole mobility than many other conjugated polymers, including the poly(phenylenevinylene)s. 2 Initially, however, rather low hole mobilities were reported for regiorandom P3HT. 3 However, when head-to-tail regioregularly substituted P3HT became available, the hole mobilities were found to be dramatically improved. [4][5][6] The increase in mobility was related to side-chain-induced self-organization into a well-ordered twodimensional lamellar structure. 2 In contrast, electron transport has not been reported up to now in P3HT, most probably because electrons are heavily trapped. Molecular oxygen impurities have been proposed as one possible trap, 7 but little has been done to systematically address the issue. The extensive literature for P3HT highlights the importance of both structural and chemical influences on transport properties.In this letter, we present results concerning carrier transport in regioregular (RR)...

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confidence: 95%

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confidence: 99%

High ambipolar and balanced carrier mobility in regioregular poly(3-hexylthiophene)

Choulis

Kim

Nelson

et al. 2004

Applied Physics Letters

207

120

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“…The film roughness increases with the thickness, being around 12% of the thickness in the full thickness range measured. This value is smaller than observed in other polythiophene derivative thin films also produced by electrosynthesis, like poly (3-hexylthiophene), PHT [11] and poly(3-methylthiophene), PMT [12]. In Fig.…”

Section: Resultsmentioning

confidence: 44%

“…From Eq. Table 1, this mobility value is compared with those obtained by us [11,12] for others polythiophene derivatives prepared by electrochemical method. Table I: Positive charge carriers mobility for polythiophene derivatives grown by electrochemical methods: poly(3-methylthiophene) (PMT) [12], poly(3-hexylthiophene) (PHT) [11] and poly (3-octylthiophene) (POT).…”

Section: From Eq (1) We Havementioning

confidence: 99%

The electronic behavior of poly(3-octylthiophene) electrochemically synthesized onto Au substrate

Valaski¹,

Moreira²,

Micaroni³

et al. 2003

Braz. J. Phys.

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We investigate the electronic characteristics and the absorption spectra of poly(3-octylthiophene), POT, films grown by electrochemical methods onto Au substrates. We discuss the results considering the morphological factor. POT films thickness can be controlled by current density in the electropolymerization process. The film roughness depends on the thickness, being about 12% of film thickness. The samples for electrical measurements were made in sandwich structure, Au/POT/metal (metal: Ni, Al). Analyzing current-voltage data we were able to estimate the positive charge carrier mobility (5×10 −4 cm 2 V −1 s −1 ) and the potential barrier height in the metal/polymer interfaces (0.1 eV for Au/POT and Ni/POT and 0.85 eV for Al/POT). I IntroductionConjugated polymers have been object of intense research in the last years. These organic semiconductors present good mechanical features, facility of production and offer the possibility of construction of devices with larger active areas than their inorganic counterparts. Among these polymers, polythiophene and its derivatives have received special considerations. Polythiophenes have a good chemical stability upon environmental conditions and produce stable interfaces with electrode metals commonly used in electronics, like aluminum and gold [1,2]. Another important feature of polythiophene films is a large absorption coefficient in the visible range of the electromagnetic spectrum [3,4,5]. These characteristics make polythiophene and its derivatives interesting materials for solar cell applications [6]. One of the major problems in polymer devices is the small charge carrier mobility. The morphology of the polymer film takes important place in this situation. In amorphous materials the transport occurs via hopping between localized states and disorder contributes to a further reduction of mobility. Many methods have been used to improve the order degree or the crystallinity in polymer films [7,8]. The use of polymers with large side chain segments is one of the methods employed with this intent. The increase in the side chain length improves the order and the planarity of the polymer chains [9]. So, the order is expected to be higher in poly(3-octylthiophene), POT, than in other polythiophene derivatives, like poly(3-metylthiophene) and consequently, also the charge carrier mobility.When a potential barrier energy ϕ for the charge carriers injection at the interface between the electrode and the polymer is so that ϕ >> kT (k is the constant of Boltzmann and T is the absolute temperature) the transport is better described by Simmons current density expression, derived for thermionic injection into low mobility materials [10].

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“…The workfunction of aluminiuml is − 4.3 eV, and the highest occupied molecular orbital (HOMO) of P3HT has been estimated to range between −5.1 and − 5.2 eV, from an SCLC analysis of hole only thin film devices [29], cyclic voltametry [30], and photoelectron spectroscopy [31]. The energy gap estimated from absorption spectroscopy is about 2.1 eV, therefore the lowest unoccupied molecular orbital (LUMO) is about − 3.0 eV.…”

Section: Methodsmentioning

confidence: 99%

Current Conduction in Poly(3-Hexylthiophene) and in Poly(3- Hexylthiophene) doped [6,6]-Phenyl C61-Butyric Acid Methylester Composite Thin Film Devices

Chiguvare¹,

Parisi²

2012

Zeitschrift Für Naturforschung A

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Transport properties of poly(3-hexylthiophene) (P3HT), and of its blend with [6,6]-phenyl C61-butyric acid methylester (PCBM), were studied by analysing temperature dependent current-voltage characteristics of spin cast thin films sandwiched between aluminium electrodes in a metal-insulatormetal (MIM) configuration. It was found that in Al/P3HT/Al devices, the current is limited by space charge that accumulates near the hole injecting electrode due to the poor bulk transport properties of P3HT. At low temperatures and high applied electric fields the current density obeys a power law of the form J ∼ V m , characteristic of space charge limited current (SCLC) in the presence of exponentially distributed traps within the band gap. These traps are filled by charge that is injected by quantum mechanical tunnelling, which is adequately described by the Fowler-Nordheim (FN) theory. By calculating the majority charge carrier mobility in Al/P3HT/Al and Al/P3HT:PCBM/Al devices from the Ohmic, SCLC, and FN tunnelling fits at different temperatures, we have obtained that the charge carrier mobility in P3HT is two orders smaller than the electron mobility in the P3HT:PCBM blend at room temperature, but comparable at low temperatures. This information is important in determining the origin of open circuit voltage and short circuit current limit in solar cells that employ this blend as the active layer.

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Charge injection and transport in electrochemical films of poly(3-hexylthiophene)

Cited by 40 publications

References 29 publications

High ambipolar and balanced carrier mobility in regioregular poly(3-hexylthiophene)

High ambipolar and balanced carrier mobility in regioregular poly(3-hexylthiophene)

The electronic behavior of poly(3-octylthiophene) electrochemically synthesized onto Au substrate

Current Conduction in Poly(3-Hexylthiophene) and in Poly(3- Hexylthiophene) doped [6,6]-Phenyl C61-Butyric Acid Methylester Composite Thin Film Devices

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