High work-function hole transport layers by self-assembly using a fluorinated additive

Mauger, Scott A.; Li, Jun; Özmen, Özge Tüzün; Yang, Andy Y.; Friedrich, S.; Rail, M. Diego; Berben, Louise A.; Moulé, Adam J.

doi:10.1039/c3tc30973h

Cited by 21 publications

(42 citation statements)

References 33 publications

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“…The increased intensity of the pre-edge peak indicates an increased density of delocalized hole states in the SeP3MEET backbone, corresponding to p-type doping. Similar results have also been reported for the p-type doping of P3HT by PSS [13] and SeP3MEET doped with a PFI, Nafion [16]. In addition, the peak around 293 eV (associated with s * CÀF excitations [41,42]) also increases in intensity as expected due to the presence of F4TCNQ.…”

Section: Molecular Doping Of the Polar Layersupporting

confidence: 75%

“…As can be seen, significant changes are observed between the doped and undoped SeP3MEET films. The peak at 285.2 eV, which corresponds to the C1s(C]C) / p * C¼C transition and is associated with aromatic carbons in the thiophene rings, increases dramatically upon p-doping [16,39,40]. Note that no linear combination of the spectra from pure F4TCNQ and SP3MEET can account for the increased intensity of the pre-edge peak.…”

Section: Molecular Doping Of the Polar Layermentioning

confidence: 99%

“…The increased intensity at 300 eV is likely due to the subtle structural rearrangement of SeP3MEET with more side-chains at the film/air interface after annealing. Given that the spectra of doped films at mild and high heating are quite similar, it implies that unlike PFI doped SeP3MEET, where the doping process occurs only at elevated temperature [16], F4TCNQ doping occurs spontaneously.…”

Section: Molecular Doping Of the Polar Layermentioning

confidence: 99%

“…It was shown that PFI tends to phase separate out of the polymer due to its low miscibility in conjugated polymers, forming a PFI-rich skin between SeP3MEET and poly(3-hexylthiophene) (P3HT) layers. In this case, the location of the dopant remains stable under considerable thermal stress, which implies that reduced mixing can hinder undesired doping [16]. This relationship between ionic dopant miscibility and contact doping across a polar/non-polar interface was recently quantified for a variety of self-doped polymers [17].…”

mentioning

confidence: 99%

“…1), will be used to fabricate the polar and non-polar layers, respectively. SeP3MEET and P3HT are chosen because 1) both materials have similar polythiophene backbones; 2) P3HT is the most widely used conjugated polymer while SeP3MEET has been shown as a promising alternative to PEDOT:PSS [28,16], and 3) SeP3MEET forms a thermally stable bilayer with P3HT, so we can study the transport of F4TCNQ without interference from mixing between the layers. The first part of this paper explores whether F4TCNQ is able to dope SeP3MEET.…”

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The effect of thermal annealing on dopant site choice in conjugated polymers

Rochester

Jacobs

et al. 2016

Organic Electronics

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a b s t r a c tSolution-processed organic electronic devices often consist of layers of polar and non-polar polymers. In addition, either of these layers could be doped with small molecular dopants. It is extremely important for device stability to understand the diffusion behavior of these molecular dopants under the thermal stress and whether the dopants have preference for the polar or the non-polar polymer layers. In this work, a widely used molecular dopant 2, 3,5,7,8, was chosen to investigate dopant site preference upon thermal annealing between the polar thiophene poly(thiophene-3-[2-(2-methoxy-ethoxy)ethoxy]-2,5-diyl) (SeP3MEET) and non-polar thiophene poly(3-hexylthiophene) (P3HT). F4TCNQ is able to p-type dope both P3HT and SeP3MEET. Further doping studies of SeP3MEET using near edge X-ray absorption fine structure spectroscopy, conductivity measurements and atomic force microscopy show that the F4TCNQ additive competes for doping sites with the covalently attached dopants on the SeP3MEET. Calorimetry measurements reveal that the F4TCNQ interacts strongly with the side-chains of the SeP3MEET, increasing the melting temperature of the side-chains by 30 C with 5 wt% dopant loading. Next, the thermal stability of doping in the polar/ non-polar (SeP3MEET/P3HT) bilayer architectures was investigated. Steady-state absorbance and fluorescence results show that F4TCNQ binds much more strongly in SeP3MEET than P3HT and very little F4TCNQ is found in the P3HT layer after annealing. In combination with reflectometry measurements, we show that F4TCNQ remains in the SP3MEET layer with annealing to 210 C even though the sublimation temperature for neat F4TCNQ is about 80 C. In contrast, F4TCNQ slowly diffuses out of P3HT at room temperature. We attribute this difference in binding the F4TCNQ anion to the ability of the ethyl-oxy side-chains of the SeP3MEET to orient around the charged dopant molecule and thereby to stabilize its position. This study suggests that polar side-chains could be engineered to increase the thermal stability of molecular dopant position.

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Section: Molecular Doping Of the Polar Layersupporting

confidence: 75%

Section: Molecular Doping Of the Polar Layermentioning

confidence: 99%

Section: Molecular Doping Of the Polar Layermentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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The effect of thermal annealing on dopant site choice in conjugated polymers

Rochester

Jacobs

et al. 2016

Organic Electronics

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Hole Transporting Layers in Printable Solar Cells

Curiel

Más‐Montoya

2017

Printable Solar Cells

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Perfluorinated Ionomer‐Modified Hole‐Injection Layers: Ultrahigh‐Workfunction but Nonohmic Contacts

Belaineh

Tan

Png

et al. 2015

Adv Funct Materials

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Recently it has been reported that Nafion oligomers, i.e., 2‐(2‐sulfonatotetrafluoroethoxy)‐2‐trifluoromethyltrifluoroethoxyfunctionalized oligotetrafluoroethylenes, also called perfluorinated ionomers (PFIs), can be blended into poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDT:PSSH) films to increase their workfunctions beyond 5.2 eV. These PFI‐modified films are useful for energy‐level alignment studies, and have been proposed as hole‐injection layers (HILs). It is shown here however that these HILs do not provide sufficiently fast hole transfer into adjacent polymer semiconductor layers with ionization potentials deeper than ≈5.2 eV. X‐ray and ultraviolet photoemission spectroscopies reveal that these HILs exhibit a molecularly‐thin PFI overlayer that sets up a surface dipole that provides the ultrahigh workfunction. This dipolar layer persists even when the subsequent organic semiconductor layer is deposited, as evidenced by measurements of the diode built‐in potentials. As a consequence, the PFI‐modified HILs produce a higher contact resistance, and a lower equilibrium density of holes at the semiconductor contact than might have been expected from simple thermodynamic considerations of the reduction in hole‐injection barrier. Thus the use of insulating dipolar surface layers at the charge‐injection contact to tune its workfunction to match the relevant transport level of the semiconductor is of limited utility to achieve ohmic contact in these devices.

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High work-function hole transport layers by self-assembly using a fluorinated additive

Cited by 21 publications

References 33 publications

The effect of thermal annealing on dopant site choice in conjugated polymers

The effect of thermal annealing on dopant site choice in conjugated polymers

Hole Transporting Layers in Printable Solar Cells

Perfluorinated Ionomer‐Modified Hole‐Injection Layers: Ultrahigh‐Workfunction but Nonohmic Contacts

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