Influence of the Emission Layer Thickness on the Optoelectronic Properties of Solution Processed Organic Light-Emitting Diodes

Höfle, Stefan; Lutz, Tobias; Egel, Amos; Nickel, Felix; Kettlitz, Siegfried W.; Gomard, Guillaume; Lemmer, Uli; Colsmann, Alexander

doi:10.1021/ph500186m

Cited by 46 publications

(39 citation statements)

References 37 publications

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“…The emission properties of fluorophores as a function of thickness when deposited on nonmetallic substrates has been reported. [70][71][72][73][74] No emission was expected for Rh6G on the gold surface since metals typically quench fluorescence. In contrast, Rh6G can be observed in SERS down to single molecule levels when adsorbed to metal nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

A comparison of SERS and MEF of rhodamine 6G on a gold substrate

Kohr

Karawdeniya

Dwyer

et al. 2017

Phys. Chem. Chem. Phys.

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Rhodamine 6G is spin-cast onto gold surfaces and the reflectance, emission, excitation, and SERS spectra are reported. Electron microscopy shows that the particle sizes of the gold are uniform for all preparations. Reflection spectra show that the Rh6G aggregates for thicker films and that the gold plasmon band shifts due to the refractive index change on the surface. The intensity of the SERS spectra increases with increasing surface coverage but the rate of change modulates between submonolayer and multilayer surface densities. The emission spectra behave unexpectedly as a function of Rh6G coverage. At submonolayer coverage the emission is relatively strong, decreases as the surface density increases to a monolayer, and then increases as the Rh6G thickness increases. Excitation spectra demonstrate that the emitting species at low surface density is monomeric but for thicker layers the excited state responsible for emission is Rh6G aggregates. For the thicker films, the Rh6G acts as its own dielectric layer for metal enhanced fluorescence of the aggregates.iii ACKNOWLEDGMENTS

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Section: Introductionmentioning

confidence: 99%

A comparison of SERS and MEF of rhodamine 6G on a gold substrate

Kohr

Karawdeniya

Dwyer

et al. 2017

Phys. Chem. Chem. Phys.

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“…The 150 nm thick bottom electrodes were doctor bladed from the PEDOT:PSS formulation Clevios HY E (Heraeus Deutschland GmbH & Co. KG), including dispersed AgNWs in air on a hot plate (65 °C) by using a universal thin‐film applicator (Zehntner ZUA 2000) with an applicator gap of 220 μm. During layer deposition, the applicator was accelerated from 10 to 80 mm s −1 to compensate the solution mass loss, which would otherwise lead to continuously decreasing layer thicknesses in the direction of coating . The PEDOT:PSS:AgNW‐coated and patterned PET substrates were flattened by hot‐pressing using an imprint tool (CNI, NIL Technology) and the temperature and pressure profiles are depicted in Figure b.…”

Section: Methodsmentioning

confidence: 99%

“…Complying with industrially relevant layer-deposition processes,w ed octor bladed the photoactive layer onto 2.5 7.5 cm 2 PET substrates,e ach carrying 18 devices of 0.22 cm 2 each on top of the optimized bottom HYE as depicted in Figure 4a.B ya ccelerating the coating bar during the layer deposition, we produced a wedge-shaped absorber layer on top of the electrode array. [12,39] Thet hickness gradient becomes visible in the interferences of the reflected light in the photograph in Figure 4b.T his experimental setup allowed us to study multiple layer thicknesses and their effect on the optoelectronic devicep roperties on one sample and within one experiment. Thed evices were completed by doctorb lading a1 50 nm thick HYE on top of the device.F igure 4c depicts the dependencies of the J SC and VLTo nt he photoactivel ayer thickness of the solar cells along the coating direction.…”

Section: All-solution-processed Solar Cellsmentioning

confidence: 98%

“…Complying with industrially relevant layer‐deposition processes, we doctor bladed the photoactive layer onto 2.5×7.5 cm 2 PET substrates, each carrying 18 devices of 0.22 cm 2 each on top of the optimized bottom HYE as depicted in Figure a. By accelerating the coating bar during the layer deposition, we produced a wedge‐shaped absorber layer on top of the electrode array . The thickness gradient becomes visible in the interferences of the reflected light in the photograph in Figure b.…”

Section: All‐solution‐processed Solar Cellsmentioning

confidence: 99%

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Hot‐Pressed Hybrid Electrodes Comprising Silver Nanowires and Conductive Polymers for Mechanically Robust, All‐Doctor‐Bladed Semitransparent Organic Solar Cells

et al. 2018

Self Cite

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Future low‐cost, high‐throughput production of organic solar cells in roll‐to‐roll printing processes calls for all‐solution‐processable device architectures. Mechanical flexibility and robustness are mandatory to roll the solar foils during printing and to eventually comply with certain end‐user requirements. Here, we report on semitransparent organic solar cells, comprising top and bottom silver nanowire (AgNW) electrodes that were embedded into conductive poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The devices exhibited excellent robustness in bending experiments with radii of 5 and 2.5 mm as well as upon folding. To avoid short circuits from nanowires that could stick out of the bottom electrodes, the PEDOT:PSS:AgNW layers were flattened by hot‐pressing after deposition. All solar cells were fabricated in air by doctor blading and exhibited a clear (haze‐free) transparency due to the absence of bus bars. On photoactive areas of 0.5 cm2, power conversion efficiencies of 3.8 % were obtained.

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“…[22,23] Thickness gradients can be easily fabricated by blade coating [24] and indeed have been employed as a demonstration for the potential of gradients in the optimization of organic photovoltaics (OPV) and organic light emitting diodes (OLEDs) at laboratory scale. [24,25] The local evaluation of performance is typically done by using techniques such as light beam induced current (LBIC), micro-electroluminescence or lock-in thermography. [26] While these techniques are commonly employed for other types of studies, such as degradation studies, they can be equally suited for the inspection of samples intendedly fabricated with lateral inhomogeneities.…”

Section: Introductionmentioning

confidence: 99%

High‐Throughput Multiparametric Screening of Solution Processed Bulk Heterojunction Solar Cells

Sánchez-Díaz

Rodríguez‐Martínez

Córcoles-Guija

et al. 2018

Adv Elect Materials

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(MDMO-PPV) or poly(3-hexylthiophene) (P3HT) combined with soluble fullerenes, [6,7] up to current PCE values exceeding 10% for several systems. [9][10][11][12][13] There is no specific fundamental limitation to organic materials that indicates that much higher values are not possible, and the number of potential candidates is nearly infinite. Indeed, the organic nature of the photoactive materials offers a myriad of possibilities to modify their chemical structure; for the case of conjugated polymers, there exists a vast assortment of combinations depending on the choice of moieties, the bridging atoms, the length and branching points of the alkyl side chains, and the molecular weight, to name but a few. Using search engines to inspect the literature, we estimate that in the last ten years ≈5000 organic conjugated materials have been tested in BHJ solar cells, albeit only a few tenths have been studied and optimized in depth. While applied quantum theory can help to select promising candidates, [14][15][16] the final performance often depends on a number of issues difficult to predict a priori, such as solubility, miscibility of compounds, tendency to crystallize, exact energy levels in the blend, etc. In practice, this means that for a given promising backbone, a family of systems need to be tested, including different side chains, molecular weights, donor:acceptor combinations, etc. [17] Within this large and uncharted spectrum of materials and processing variables, combinatorial screening methodologies are highly on demand to speed up their exploration while helping the technology to approach the theoretical Shockley-Queisser limit of >20% PCE. [18,19] From the engineering point of view, three main aspects must be addressed for the evaluation of a material system for BHJ solar cells, namely the active layer thickness, the donor-acceptor (D:A) blending ratio and the nanoscale morphology (typically controlled by deposition conditions, thermal annealing, and use of additives). Ideally, those three variables can be optimized separately and to some extent it is usually an acceptable approximation; however, the full potential of a novel active layer material requires for fine tuning of the preparation conditions that take into consideration the subtle interplay between them. [20] For instance, the optimum thickness is often found close to the first interference maximum, which is governed by the refractive index of the active layer; this, on the other hand, will be a function of the D:A ratio (fullerenes typically have higher refractive index than polymers) and the degree of crystallinity One of the major bottlenecks in the development of organic photovoltaics is the time needed to evaluate each material system. This time ranges from weeks to months if different variables such as blend composition, thickness, annealing, and additives are to be explored. In this study, the use of lateral gradients is proposed in order to evaluate the photovoltaic potential of a material system up to 50 times faster. A platform that c...

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Influence of the Emission Layer Thickness on the Optoelectronic Properties of Solution Processed Organic Light-Emitting Diodes

Cited by 46 publications

References 37 publications

A comparison of SERS and MEF of rhodamine 6G on a gold substrate

A comparison of SERS and MEF of rhodamine 6G on a gold substrate

Hot‐Pressed Hybrid Electrodes Comprising Silver Nanowires and Conductive Polymers for Mechanically Robust, All‐Doctor‐Bladed Semitransparent Organic Solar Cells

High‐Throughput Multiparametric Screening of Solution Processed Bulk Heterojunction Solar Cells

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