n‐Doping of Organic Electronic Materials using Air‐Stable Organometallics

Guo, Song; Kim, Sang Bok; Mohapatra, Swagat K.; Qi, Yabing; Sajoto, T.; Kahn, Antoine; Marder, Seth R.; Barlow, Stephen

doi:10.1002/adma.201103238

Cited by 171 publications

(177 citation statements)

References 22 publications

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“…16 Dimeric organometallic reductants of the same class as those used in the C 60 study have also been used to n-dope materials processed from solution, including the polymer poly{[N,N 0 -bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5 0 -(2,2 0 -bithiophene)}, P(NDI 2 OD-T 2 ). 20,21 We show here that the charge-transport properties of films cast from solution containing P(NDI 2 OD-T 2 ) and ultra-low concentrations of the organometallic n-dopant pentamethylrhodocene dimer, [RhCp*Cp] 2 , follow a similar dependence on dopant concentration to that previously seen for C 60 .…”

supporting

confidence: 69%

“…24,25 The concentration of P(NDI 2 OD-T 2 ) in toluene was kept constant at 10 mg/ml throughout all measurements to achieve uniform film thicknesses across devices. The dopant solution was added to the host solution in very small amounts, ranging from 7.8 Â 10 À5 to 7.8 Â 10 À3 molar ratio (MR), which correspond to doping densities of 6 Â 10 16 to 6 Â 10 18 26,27 and previous experiments on the closely related rhodocene dimer/ P(NDI 2 OD-T 2 ) system 20,21 indicate the feasibility of the reaction, as shown in Fig. 1.…”

mentioning

confidence: 89%

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Dopant controlled trap-filling and conductivity enhancement in an electron-transport polymer

Higgins

Mohapatra

Barlow

et al. 2015

Applied Physics Letters

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Charge transport in organic semiconductors is often inhibited by the presence of tail states that extend into the band gap of a material and act as traps for charge carriers. This work demonstrates the passivation of acceptor tail states by solution processing of ultra-low concentrations of a strongly reducing air-stable organometallic dimer, the pentamethylrhodocene dimer, [RhCp*Cp]2, into the electron transport polymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}, P(NDI2OD-T2). Variable-temperature current-voltage measurements of n-doped P(NDI2OD-T2) are presented with doping concentration varied through two orders of magnitude. Systematic variation of the doping parameter is shown to lower the activation energy for hopping transport and enhance film conductivity and electron mobility.

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confidence: 69%

mentioning

confidence: 89%

Dopant controlled trap-filling and conductivity enhancement in an electron-transport polymer

Higgins

Mohapatra

Barlow

et al. 2015

Applied Physics Letters

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“…Through structural optimization they achieve electrical conductivities and thermoelectric power factors as high as 0.5 S.cm −1 and 1.4 μW.m −1 K −2 , respectively. A variety of new organometallic complexes, 87 hydride donors, 1,3-Dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole (DMBI), 88 and…”

Section: N-type Organic Thermoelectric Materialsmentioning

confidence: 99%

Review—Organic Materials for Thermoelectric Energy Generation

Cowen

Atoyo

Carnie

et al. 2017

ECS J. Solid State Sci. Technol.

130

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Organic semiconductor materials have been promising alternatives to their inorganic counterparts in several electronic applications such as solar cells, light emitting diodes, field effect transistors as well as thermoelectric generators. Their low cost, light weight and flexibility make them appealing in future applications such as foldable electronics and wearable circuits using printing techniques. In this report, we present a mini-review on the organic materials that have been used for thermoelectric energy generation. The reduction in the effects of climate change, caused by the burning of fossil fuels, has recently been given increased emphasis by major world governments and it is therefore necessary to consider the efficiency of the methods we currently use to generate energy. It has previously been estimated that 63% of global energy consumption is wasted with the major form of this waste being heat.1,2 It is therefore important to develop methods of reconverting this wasted heat back in to useful forms of energy, such as electricity.Thermoelectric generators (TEG) are a promising technology which make use of a process known as the Seebeck effect for heat recovery. The Seebeck effect can be described as two dissimilar conductors or semiconductors connected thermally in parallel and electrically in series and exposed to a temperature gradient causing a difference in voltage between the two materials.3,4 In a TEG one p-type and one ntype semiconductor make use of the Seebeck effect by connecting one to the other electrically in series and thermally in parallel; a general device setup is shown in Figure 1. By connecting the two components, by a junction which is heated, the n-type component of the device transports electrons from the hot junction to a heat sink while the p-type material transports positively charged holes along the same direction of the temperature gradient. The reverse is also possible if the holes and electrons flow away from a cold connecting junction to a heated point at the end of each semiconductor, this induces a constant cooling at the junction through the Peltier effect. 4,5The quantification of the Seebeck effect, in a specific material, is given by the Seebeck coefficient, α, and is the open circuit voltage of a material subjected to a temperature gradient, commonly with units on the scale of μVK −1 to mVK −1 . 6 A materials overall efficiency in the conversion of heat to electricity is given by the dimensionless figure of merit, ZT, defined as,where σ is the electrical conductivity and κ is the thermal conductivity. [6][7][8] It is therefore necessary for thermoelectric materials to have a high electrical conductivity and a low thermal conductivity making electrically conducting metals inappropriate for thermoelectric applications due to their high thermal conductivities and low z E-mail: m.j.carnie@swansea.ac.uk; derya.baran@kaust.edu.sa; b.c.schroeder@qmul .ac.uk Seebeck coefficients. The ideal thermoelectric materials should be an electrical crystal to maximize σ and at the s...

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“…[14] Therefore, finding a molecular donor, compatible with both vacuum-deposition and solution processes such as drop-casting, is desirable to be incorporated as a WF-reducer for bottom and top electrodes into all-solution processed or multilayer devices. [17]- [18] The dimers formed by some 19-electron organometallic sandwich compounds, such as the dimer of 1,2,3,4,5-pentamethylrhodocene (1 2 , molecular structure shown in Figure 1), are promising candidates for this purpose: their reductant ability has already been demonstrated by the effective n-doping for a variety of organic semiconductors, [19] their 18-electron configurations lead to moderate air-stability, and they can be processed using both vacuum deposition at low temperature (~120 ºC) and solution processes. [19] Indeed, the Ir analogue of 1 2 has been used to reduce the WF of ITO, ZnO, and Au via dip-coating, [20] and the dimer of ruthenium pentamethylcyclopentadienyl mesitylene has been shown to reduce the WF of ITO by dip-coating [20] and that of ZnO through vacuum processing, [21] and 1 2 has been used to reduce the WF of CVD graphene by dip-coating.…”

Section: Introductionmentioning

confidence: 99%

“…In the present case, the interfacial electron transfer converts the neutral 1 2 to the cationic monomers of 1 2 (1 + ). [11], [19], [20] The positive potential caused by the resulting surface layer of 1 + cations leads to the WF reduction of the substrates.…”

Section: Introductionmentioning

confidence: 99%

Effective Work Function Reduction of Practical Electrodes Using an Organometallic Dimer

Akaike

Nardi

Oehzelt

et al. 2016

Adv Funct Materials

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The control of the cathode work function (WF) is essential to enable efficient electron injection and extraction at organic semiconductor/cathode interfaces in organic electronic devices. The adsorption of an air-stable molecular donor onto electrodes, compatible with both evaporation and solution processes, is a simple way to reduce the WF. Such a versatile molecule, however, has not been identified yet. In this paper, ultraviolet photoelectron spectroscopy is used to confirm that depositing an ultrathin layer of the moderately air-stable pentamethylrhodocene-dimer onto various conducting electrodes, by either vacuum 2 deposition or drop-casting from solution, substantially reduces their WF to less than 3.6 eV, with 2.8 eV being the lowest attainable value. Detailed measurements of the Rh core levels with X-ray photoelectron spectroscopy reveal that the electron transfer from the molecule to the respective substrates is responsible for the appreciable WF reduction. Notably, even after air-exposure, the WF of the donor-covered electrodes remains below those of typically used clean cathode-metals such as Al and Ag, rendering the approach appealing for practical applications. The WF reduction, together with the observed air-stability of the covered electrodes, demonstrates the applicability of the pentamethylrhodocene-dimer to reduce the WF for a wide range of electrodes used in all-organic or organic-inorganic hybrid devices.

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n‐Doping of Organic Electronic Materials using Air‐Stable Organometallics

Cited by 171 publications

References 22 publications

Dopant controlled trap-filling and conductivity enhancement in an electron-transport polymer

Dopant controlled trap-filling and conductivity enhancement in an electron-transport polymer

Review—Organic Materials for Thermoelectric Energy Generation

Effective Work Function Reduction of Practical Electrodes Using an Organometallic Dimer

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