Determining doping efficiency and mobility from conductivity and Seebeck data of n-doped C<sub>60</sub>
 layers

Menke, Torben; Ray, Debraj; Kleemann, Hans; Leo, Karl; Riede, Moritz

doi:10.1002/pssb.201552088

Cited by 13 publications

(10 citation statements)

References 22 publications

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“…Although the barrier value derived from the fitting of the case without the IL is larger than the maximum barrier, this difference is quite small and negligible. Carrier mobility fluctuation caused by IL penetration into the C 60 layer has been studied by Menke et al They investigated different ILs in different concentrations inside the C 60 layer and showed that there might be a reduction in carrier mobility with an increase in the dopant concentration in n -C 60 due to stronger scattering of carriers.…”

Section: Resultsmentioning

confidence: 99%

Ionically Gated Small-Molecule OPV: Interfacial Doping of Charge Collector and Transport Layer

Saranin

Mahmoodpoor

Voroshilov

et al. 2021

ACS Appl. Mater. Interfaces

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We demonstrate an improvement in the performance of organic photovoltaic (OPV) systems based on small molecules by ionic gating via controlled reversible n-doping of multi-wall carbon nanotubes (MWCNTs) coated on fullerene electron transport layers (ETLs): C60 and C70. Such electric double-layer charging (EDLC) doping, achieved by ionic liquid (IL) charging, allows tuning of the electronic concentration in MWCNTs and the fullerene planar acceptor layers, increasing it by orders of magnitude. This leads to the decrease of the series and increase of the shunt resistances of OPVs and allows use of thick (up to 200 nm) ETLs, increasing the durability of OPVs. Two stages of OPV enhancement are described upon the increase of gating bias V g: at small (or even zero) V g, the extended interface of ILs and porous transparent MWCNTs is charged by gating, and the fullerene charge collector is significantly improved, becoming an ohmic contact. This changes the S-shaped J–V curve via improving the electron collection by an n-doped MWCNT cathode with an ohmic interfacial contact. The J–V curves further improve at higher gating bias V g due to the increase of the Fermi level and decrease of the MWCNT work function. At the next qualitative stage, the acceptor fullerene layer becomes n-doped by electron injection from MWCNTs while ions of ILs penetrate into the fullerene. At this step, the internal built-in field is created within OPV, which helps in exciton dissociation and charge separation/transport, increasing further the J sc and the fill factor. The ionic gating concept demonstrated here for most simple classical planar small-molecule OPV cells can be potentially applied to more complex highly efficient hybrid devices, such as perovskite photovoltaic with an ETL or a hole transport layer, providing a new way to tune their properties via controllable and reversible interfacial doping of charge collectors and transport layers.

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Section: Resultsmentioning

confidence: 99%

Ionically Gated Small-Molecule OPV: Interfacial Doping of Charge Collector and Transport Layer

Saranin

Mahmoodpoor

Voroshilov

et al. 2021

ACS Appl. Mater. Interfaces

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“…While an influence of the EA of tetracyanoquinodimethane (TCNQ)-based molecules was observed, a quantitative understanding of its influence is still missing. Similarly, in studies of n-doped C 60 , lower limits for the doping efficiency of various dopants were derived but without investigating the role of the energy level alignment between host and dopant . Here, we study a series of amorphous host materials with gradually increasing IE to uncover its influence on the host–dopant charge transfer efficiency, conductivity, and thermoelectric properties.…”

Section: Introductionmentioning

confidence: 99%

Influence of Dopant–Host Energy Level Offset on Thermoelectric Properties of Doped Organic Semiconductors

et al. 2018

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Increasing the amount of charge carriers by molecular doping is important to improve the function of several organic electronic devices. In this work, we use highly fluorinated fullerene (C 60 F 48) to p-type dope common amorphous molecular host materials. We observe a general relation between the material's electrical conductivity and Seebeck coefficient, both strongly depending on the energy level offset between amorphous host and dopant. This suggests that the doping efficiency at similar doping levels is mainly determined by the electron transfer yield from host to dopant. Indeed, the dopant anion and host cation absorption strength correlate with the ionization energy (IE) of the host material. Host materials with an IE significantly below the electron affinity of the dopant yield the highest doping efficiency. Surprisingly, the doping efficiency reduces only by about one order of magnitude when the IE of the host material is increased by 0.55 eV, which we attribute to the disordered nature of the host materials

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“…Modulating the charge carrier density by doping is considered a key strategy for optimizing the power factor and ZT value. [9][10][11][12] Recently, significant progress has been made in p-type organic thermoelectric studies with ZT = 0.42 by using p-type doped conjugated polymers. [13,14] Both efficient p-type and n-type TE materials are required for practical applications.…”

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confidence: 99%

N‐Type Organic Thermoelectrics: Improved Power Factor by Tailoring Host–Dopant Miscibility

et al. 2017

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In this contribution, for the first time, the polarity of fullerene derivatives is tailored to enhance the miscibility between the host and dopant molecules. A fullerene derivative with a hydrophilic triethylene glycol type side chain (PTEG-1) is used as the host and (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine n-DMBI) as the dopant. Thereby, the doping efficiency can be greatly improved to around 18% (<1% for a nonpolar reference sample) with optimized electrical conductivity of 2.05 S cm , which represents the best result for solution-processed fullerene derivatives. An in-depth microstructural study indicates that the PTEG-1 molecules readily form layered structures parallel to the substrate after solution processing. The fullerene cage plane is alternated by the triethylene glycol side chain plane; the n-DMBI dopants are mainly incorporated in the side chain plane without disturbing the π-π packing of PTEG-1. This new microstructure, which is rarely observed for codeposited thin films from solution, formed by PTEG-1 and n-DMBI molecules explains the increased miscibility of the host/dopant system at a nanoscale level and the high electrical conductivity. Finally, a power factor of 16.7 µW m K is achieved at 40% dopant concentration. This work introduces a new strategy for improving the conductivity of solution-processed n-type organic thermoelectrics.

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Determining doping efficiency and mobility from conductivity and Seebeck data of n-doped C₆₀ layers

Cited by 13 publications

References 22 publications

Ionically Gated Small-Molecule OPV: Interfacial Doping of Charge Collector and Transport Layer

Ionically Gated Small-Molecule OPV: Interfacial Doping of Charge Collector and Transport Layer

Influence of Dopant–Host Energy Level Offset on Thermoelectric Properties of Doped Organic Semiconductors

N‐Type Organic Thermoelectrics: Improved Power Factor by Tailoring Host–Dopant Miscibility

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Determining doping efficiency and mobility from conductivity and Seebeck data of n-doped C60 layers

Cited by 13 publications

References 22 publications

Ionically Gated Small-Molecule OPV: Interfacial Doping of Charge Collector and Transport Layer

Ionically Gated Small-Molecule OPV: Interfacial Doping of Charge Collector and Transport Layer

Influence of Dopant–Host Energy Level Offset on Thermoelectric Properties of Doped Organic Semiconductors

N‐Type Organic Thermoelectrics: Improved Power Factor by Tailoring Host–Dopant Miscibility

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Determining doping efficiency and mobility from conductivity and Seebeck data of n-doped C₆₀ layers