Charge Carrier Transport In Poly Research Articles

Charge carrier transport in poly(p-phenylene vinylene):methanofullerene photovoltaic blends

The charge carrier transport and energetic disorder in OC1C10-PPV:PCBM blends with different fullerene concentrations are investigated. We demonstrate that the temperature-dependent current density versus voltage (J–V) characteristics of PCBM electron-only device and OC1C10-PPV hole-only device can be accurately described using our recently introduced improved mobility model. Furthermore, the $$J-V$$ characteristics of OC1C10-PPV:PCBM blends that were measured in electron-only and hole-only devices for different wt% of PCBM can also be accurately described by the improved mobility model. Additionally, we find that the width of the Gaussian density of states $$\sigma$$ and zero-field mobility of electron and hole in OC1C10-PPV:PCBM blends are the function of wt% PCBM. For electron-only devices based on OC1C10-PPV:PCBM blends, the electron mobility gradually increases with increase in the PCBM weight ratio, while the width of the Gaussian density of states $$\sigma$$ gradually decreases with increase in the PCBM weight ratio. Surprisingly, the hole mobility and the width of the Gaussian density of states $$\sigma$$ in hole-only devices based on OC1C10-PPV:PCBM blends show an identical behavior. These results provide information about the energetic disorder and a simplified modeling of the charge transport in disordered organic semiconductors.

Electrophysical properties of poly(N-vinylcarbazole)-carbon nanotubes composite films

The specific features of charge carrier transport in poly(N-vinylcarbazole) films doped with single-wall carbon nanotubes have been investigated. The mobilities of electrons and holes in ITO-polymer composite-Al samples have been determined by the time-of-flight method and by measuring the voltage-current characteristics of steady-state currents. According to the time-of-flight experiments, in the films of a poly(N-vinylcarbazole)-0.26 wt % single-wall carbon nanotubes composite, the drift mobility of electrons lies within (1.2–4.5) × 10−6 cm2/(V s) and exceeds the mobility of holes by a factor of 5. The shape of the transient current suggests the dispersion character of transport of electrons and holes. With an increase in the concentration of single-wall nanotubes from 0.26 to 0.43 wt %, the conductivity of the composite films increases by two orders of magnitude; that is, the threshold of conductivity percolation has been achieved. A simple model is proposed to describe the transport of charge carriers in the polymer system under study.

Charge carrier dynamics in organic semiconductors by position dependent optical probing

We investigate charge carrier transport in poly-(3-hexylthiophene) films where sizable lateral photovoltaic effects are observed. Spatiotemporal measurements of the lateral photovoltage (LPV) using a local optical probe are carried out on device structures consisting of the semiconducting polymer film with a Schottky-type backcontact and a front pair of Ohmic contacts. We employ a spreading impedance approach in the context of a discrete circuit element model to obtain a quantitative understanding of the spatial dependence and the frequency response of the lateral photovoltage. An excellent agreement between theoretical model and experiment is found, leading to an understanding of the origin of LPV in organic systems.

Electrical properties of σ‐conjugated polymers with additives and their applications in sensors

AbstractThe charge carrier transport in poly[methyl(phenyl)silylene] (PMPSi) proceeds predominantly along the σ‐delocalized Si backbone with participation of interchain hopping and polaron formation. The charge carrier mobility increases with increasing electron affinity of acceptor dopands having zero dipole moments. On the other band, the hole drift mobility is influenced by the dipole moment of the dopand. The electrostatic charge‐dipole interactions cause a broadening of the energy distribution of transport states, which results in a decrease in the charge carrier mobility. An addition of organic salts leads, under the conditions of increased humidity, to an increase in electrical conductivity and capacitance. This is demonstrated on the layers PMPSi/1,5‐dimorpholino‐1,5‐diphenylpentamethinium perchlorate.

Charge carrier transport in poly(2,5-dialkoxy- p-phenylene ethynylene)s

The charge carrier transport in poly[2,5-dioctyloxy-1,4-diethynyl-phenylene- alt-2,5,-bis(2′-ethylhexyloxy)-1,4-phenylene], a poly( p-phenylene ethynylene) (PPE) derivative, was investigated by time-of-flight (TOF) measurements. The charge transport characteristics in this material are ambipolar, and the transport is dispersive, with high electron (2.2×10 −3 cm 2 V −1 s −1) and hole (1.8×10 −3 cm 2 V −1 s −1) mobilities at room temperature and at low field (3.1×10 4 V cm −1). The mobility strongly depends on the field strength, and is observed to decrease with increasing bias. The positional and energetic disorder parameters were calculated from the temperature and field dependencies of the charge mobility using a Gaussian disorder transport formalism. The positional disorder was found to be larger than the energetic disorder over the entire experimental temperature range, leading to the observed negative field dependence of the carrier mobility.

Charge carrier transport in poly[methyl(phenyl)silylene]: the effect of additives

AbstractPoly[methyl(phenyl)silylene], PMPSi, was doped with compounds of the electron acceptor type. The charge carrier mobility increases with increasing electron affinity of the acceptors having zero dipole moments. At the same time the energy distribution of hopping states narrows. On the other hand, the hole drift mobility is influenced by the dipole moment of the dopand. The electrostatic charge carrier‐dipole interaction causes a broadening of the energy distribution of transport states which results in a decrease in the charge carrier mobility. The charge carrier transport can be explained by the disordered polaronic theory, according to which the activation energy of charge carrier mobility has contributions based on the dynamic disorder, i.e. the polaronic barrier, and on the static disorder, i.e. the variation of the energy of transport states as a result of the environment. Copyright © 2001 John Wiley & Sons, Ltd.

Negative Charge Carrier Transport in Poly(methylmethacrylate-co-9-anthracenyl-methylmethacrylate) Thin Films

We have investigated the current–voltage characteristics of devices made of poly(methylmethacrylate-co-9-anthracenyl-methylmethacrylate) (10 : 1) sandwiched between aluminium electrodes. We found that the negative charge carrier mobility in this copolymer is equal to 3 × 10—11 cm2/Vs and that the negative charge carrier traps are distributed following an exponential distribution with a characteristic energy of 77 meV.

Charge injection and transport inpoly(4,4'-biphenylenevinylene)

We investigated the positive charge carrier transportin poly(4,4'-biphenylenevinylene), PBPV, thin films using Au andAl electrodes. It was observed that Au/PBPV/Al devices presentspace-charge limited transport, whereas in Al/PBPV/Al devicesthe charge transport is injection limited. The positive chargecarrier mobility was found to be approximately 6×10-9 cm2 V-1 s-1. Applying theRichardson-Schottky thermionic emission theory to Al/PBPV/Aldevices we determined the Al/PBPV barrier height for positivecharge carrier injection.

Charge carrier transport in poly(p-phenylenevinylene) light-emitting devices

The role of doping and trap states for charge carrier transport in light-emitting devices based on unsubstituted poly(p-phenylenevinylene) (PPV) was investigated and charge carrier mobilities were determined by different techniques. Using temperature dependent impedance spectroscopy and thermally stimulated currents, the energetic depth and density of states created by doping of PPV during device fabrication on different substrate materials were determined. It was found that the conversion of PPV on indium–tin oxide (ITO) substrates creates shallow traps with a depth of about 0.1–0.2 eV, which are responsible for the p-type doping of PPV and govern the room temperature device characteristics. The total density of ionized acceptors at room temperature is of the order of 1016–1017 cm-3. The temperature dependent behaviour of electrical transport quantities such as conductivity and mobility is dominated by deeper states with energies in the range 0.6–1 eV. Their density can be varied by applying a vacuum to the devices. The charge carrier mobility in PPV was determined by the time-of-flight (TOF) method on devices with the configuration ITO/PPV/Al, which is typically used in light-emitting diodes. Hole mobilities in the region of 10-5 cm2 V-1 s-1 at room temperature for an electric field of about 105 V cm-1 were obtained. Field and temperature dependent TOF measurements yielded an exponential increase in the mobility with increase in the applied field and thermally activated behaviour with activation energies between 0.4 and 0.7 eV on different samples. The values of the mobility at room temperature are consistent with space-charge limited currents, but considerably larger than the values from transient electroluminescence measurements. This indicates that the transit times obtained by the latter method are dominated by the much lower electron mobility rather than by the hole mobility. Assuming luminescence quenching within a distance of 20 nm of the Al contact, an electron mobility of about 10-8 cm2 V-1 s-1 can be estimated at room temperature and fields in the region of 105 V cm-1.

Charge carrier mobility in poly(p-phenylenevinylene) studied by the time-of-flight technique

The charge carrier transport in poly(p-phenylenevinylene) (PPV) is investigated by the time-of-flight technique. Mobilities of positive carriers in PPV are determined and the dispersive character of transport is established. The dispersion parameters are analyzed in the frame of a multiple trapping model. The drift mobility of the positive carriers is in the range of 10-5 cm2/V at room temperature for an electric field of 105 V/cm and increases with increasing field and temperature. The mobility shows thermally activated behavior with an activation energy of about 0.75 eV at zero field. It is shown that the experimental results can be interpreted by polaron transport.

Charge carrier transport in poly(phenylene vinylene) films

Peculiarities of charge carrier transport in phenyl-substituted poly(phenylene vinylene)s of various structures are considered. Time-of-flight measurements were carried out to study the influence of applied electric field, temperature and matrix polarity on the transport of charge carriers in these polymers. In poly(phenylene vinylene)s the transport of charge carriers is controlled by trapping on charged traps (charged-trap-limited band transport) and experimental data are interpreted in terms of the Poole-Frenkel model. The values of both electron mobility and hole mobility ( μ e = 2.6 × 10 −8m 2V −1 s −1 at F = 6 × 10 7V m −1 and T = 278 K, μ h = 7 × 10 −9m 2 V −1s −1 at F = 6 × 10 7V m −1 and T = 294 K) are higher than in other polymer systems.

Charge-carrier transport in poly(n-propylmethylsilane) over a wide temperature range encompassing the glass transition and the melting point

Abstract The hole drift mobility of poly(n-propylmethylsilane) showing thermochromism has been measured over a wide temperature range encompassing its glass transition temperature T g and its melting point T m. The drift mobility obeys Gill's empirical expression for the field and temperature dependences below T g. It levels off near 10-4cm2V-1s-1 with the disappearance of the field dependency above T g, and gradually decreased just below T m, where distinct thermochromism due to the change of the effective o conjugation length in the Si backbone chain was observed. Above T m the mobility increases again in the molten state. The lowering of the drift mobility due to the shortening of the o conjugation length was also observed in rapidly quenched samples which exhibited a mobility about one order of magnitude lower, strongly indicating that the effective o conjugation length in the Si backbone chain determines the charge-carrier transport properties in organopolysilanes.

Optical sensitization of charge carrier transport in poly(N-vinyl carbazole).

Abstract— The photoconductivity of thin films of poly(N‐vinyl carbazole), and poly(N‐vinyl carbazole) sensitized with a thin layer of amorphous selenium, has been measured using a ‘xerographic’ condenser discharge technique and a conventional time of flight light pulse photo‐response technique. Direct camer generation and hole mobility in the polymer was found to be strongly field dependent. There appears to be no evidence for deep trapping. Hole transport through the polymer was able to be sensitized by light absorbed in the selenium. The results indicate that the photosensitization mechanism can be thought of in terms of hole generation and transport in selenium, field‐modulated injection across the selenium polymer interface and transport through the polymer.