Trap origin of field-dependent mobility of the carrier transport in organic layers

Montero, José M.; Bisquert, Juan

doi:10.1016/j.sse.2010.09.009

Cited by 18 publications

(10 citation statements)

References 30 publications

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“…(2) is defined from the ratio of the free to total chargecarrier density, the effective mobility is usually electric field and temperature dependent. However, the band mobility is not inherently dependent on either of these quantities [19]. Note that this definition of the effective mobility does not account for nonideal injection.…”

Section: B the Mott-gurney Lawmentioning

confidence: 99%

“…Hopping charge transport in such a Gaussian DOS leads to a dependence of the (effective) mobility on the temperature, electric field, and charge-carrier density that has been parametrized by Pasveer et al and subsequently used in a series of papers describing unipolar transport in organic semiconductors [17,18]. However, it has previously been shown that exponential tails (which is a good approximation of a Gaussian in a limited energy range) or even more complex shapes of the DOS are sometimes required to describe certain aspects of the physics of organic semiconductor devices [3,[12][13][14]19,20]. For instance, molecular dynamics and tight-binding simulations on P3HT lead to a DOS that is neither a pure Gaussian nor a pure exponential tail but rather a combination of both [21].…”

Section: Introductionmentioning

confidence: 99%

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Charge Transport in Spiro-OMeTAD Investigated through Space-Charge-Limited Current Measurements

et al. 2018

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Extracting charge-carrier mobilities for organic semiconductors from space-charge-limited conduction measurements is complicated in practice by nonideal factors such as trapping in defects and injection barriers. Here, we show that by allowing the bandlike charge-carrier mobility, trap characteristics, injection barrier heights, and the shunt resistance to vary in a multiple-trapping drift-diffusion model, a numerical fit can be obtained to the entire current density-voltage curve from experimental space-charge-limited current measurements on both symmetric and asymmetric 2; 2 0 ; 7; 7 0 -tetrakis(N; N-di-4-methoxyphenylamine)-9; 9 0 -spirobifluorene (spiro-OMeTAD) single-carrier devices. This approach yields a bandlike mobility that is more than an order of magnitude higher than the effective mobility obtained using analytical approximations, such as the Mott-Gurney law and the moving-electrode equation. It is also shown that where these analytical approximations require a temperature-dependent effective mobility to achieve fits, the numerical model can yield a temperature-, electric-field-, and charge-carrier-density-independent mobility. Finally, we present an analytical model describing trap-limited current flow through a semiconductor in a symmetric single-carrier device. We compare the obtained charge-carrier mobility and trap characteristics from this analytical model to the results from the numerical model, showing excellent agreement. This work shows the importance of accounting for traps and injection barriers explicitly when analyzing current density-voltage curves from space-charge-limited current measurements.

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Section: B the Mott-gurney Lawmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Charge Transport in Spiro-OMeTAD Investigated through Space-Charge-Limited Current Measurements

et al. 2018

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“…Transport occurs through polaron hopping between these states, which have a distribution of energies. In the last few years, many groups, for example, [1][2][3][4][5][6][7][8] have shown that charge transport in polymers can only be understood by invoking deep traps, that is, charge states whose energies lie too deep in the band gap in concentrations too great to be accounted by tail states in the energetic distribution.…”

Section: Introductionmentioning

confidence: 99%

Mesoscopic kinetic Monte Carlo modeling of organic photovoltaic device characteristics

et al. 2012

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Measured mobility and current-voltage characteristics of single layer and photovoltaic (PV) devices composed of poly{9,9-dioctylfluorene-co-bis[N,N -(4-butylphenyl)]bis(N,N -phenyl-1,4-phenylene)diamine} (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) have been reproduced by a mesoscopic model employing the kinetic Monte Carlo (KMC) approach. Our aim is to show how to avoid the uncertainties common in electrical transport models arising from the need to fit a large number of parameters when little information is available, for example, a single current-voltage curve. Here, simulation parameters are derived from a series of measurements using a self-consistent "building-blocks" approach, starting from data on the simplest systems. We found that site energies show disorder and that correlations in the site energies and a distribution of deep traps must be included in order to reproduce measured charge mobility-field curves at low charge densities in bulk PFB and F8BT. The parameter set from the mobility-field curves reproduces the unipolar current in single layers of PFB and F8BT and allows us to deduce charge injection barriers. Finally, by combining these disorder descriptions and injection barriers with an optical model, the external quantum efficiency and current densities of blend and bilayer organic PV devices can be successfully reproduced across a voltage range encompassing reverse and forward bias, with the recombination rate the only parameter to be fitted, found to be 1 × 10 7 s −1 . These findings demonstrate an approach that removes some of the arbitrariness present in transport models of organic devices, which validates the KMC as an accurate description of organic optoelectronic systems, and provides information on the microscopic origins of the device behavior.

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“…Space‐charge‐limited current (SCLC) is as an adequate technique employed to study the intrinsic bulk charge transport properties of a semiconductive single crystal . The pioneering work by Karl and co‐workers had aroused the extensive investigations of the bulk charge transport in OSCs, which elucidated the physical understanding of the motion of carriers in organic molecular semiconducting materials. In a number of studies characterizing the electrical properties along the vertical direction out of the ab ‐planes, thermal activation transport through the vertical direction has been observed.…”

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confidence: 99%

Vertical Charge Transport via Small Polaron Hopping within TIPS‐Pentacene Lamellar Single Crystal

Wang

Liu

Dong

et al. 2017

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A modified liquid method is employed to grow an ultralarge 6,13-bis(triisopropylsilylethynyl)pentacene crystal, ensuring fabrication and measurements of the two terminal devices. The hole transport mechanism is studied by analyzing the space charge limited currents (SCLCs) at various temperatures. Modified SCLC theory with a small polaron hopping model is developed and employed to successfully simulate the I-V curves. Values of effective hopping distance, transfer integral, and reorganization energy are extracted and reasonably discussed. A scenario is suggested that hopping transport takes place from one molecule to its nearest neighbor along the c-axis, with every molecule acting as a trapping center.

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Trap origin of field-dependent mobility of the carrier transport in organic layers

Cited by 18 publications

References 30 publications

Charge Transport in Spiro-OMeTAD Investigated through Space-Charge-Limited Current Measurements

Charge Transport in Spiro-OMeTAD Investigated through Space-Charge-Limited Current Measurements

Mesoscopic kinetic Monte Carlo modeling of organic photovoltaic device characteristics

Vertical Charge Transport via Small Polaron Hopping within TIPS‐Pentacene Lamellar Single Crystal

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