Gerardo Hernandez-sosa

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Organization: Karlsruhe Institute of Technology (KIT)

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Material Chemistry

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Organic Chemistry

OLED

Chemicals
References

Sulfone-Based Deep Blue Thermally Activated Delayed Fluorescence Emitters: Solution-Processed Organic Light-Emitting Diodes with High Efficiency and Brightness

Co-reporter:Nils Jürgensen, Andreas Kretzschmar, Stefan Höfle, Jan Freudenberg, Uwe H. F. Bunz, and Gerardo Hernandez-Sosa

Chemistry of Materials November 14, 2017 Volume 29(Issue 21) pp:9154-9154

Publication Date(Web):October 23, 2017

DOI:10.1021/acs.chemmater.7b02964

Low efficiencies of soluble blue emitter materials remain a major issue in the development of printed organic light-emitting devices. n-Alkylated carbazoles or sterically demanding ortho-substituted diphenylamines were employed as donor elements to increase solubility and to preserve blue emission of thermally activated delayed fluorescence (TADF) donor–acceptor–donor emitters employing a p-bis(phenylsulfonyl)benzene acceptor described in the literature. The soluble molecules exhibited increased steric hindrance of the amine donors and a small ΔEST as low as 0.32 eV. Thermally activated delayed fluorescence occurs, and photoluminescence quantum yields of ≤82% were achieved. Application of these TADF molecules in solution-processed organic light-emitting diodes resulted in high brightnesses of ≤10000 cd/m2, current efficiencies of ≤9.5 cd/A, and external quantum efficiencies of ≤8.5%, while retaining deep blue emission ranging from 466 to 436 nm with color coordinates low as CIEy = 0.08.

High-Performance Electron Injection Layers with a Wide Processing Window from an Amidoamine-Functionalized Polyfluorene

Co-reporter:Uwe H. F. Bunz;Martin Petzoldt;Sebastian Dück;Sebastian Stolz;Uli Lemmer;Manuel Hamburger;Michael Sendner

ACS Applied Materials & Interfaces May 25, 2016 Volume 8(Issue 20) pp:12959-12967

Publication Date(Web):2017-2-22

DOI:10.1021/acsami.6b03557

In this work, we present organic light-emitting diodes (OLEDs) utilizing a novel amidoamine-functionalized polyfluorene (PFCON-C) as an electron injection layer (EIL). PFCON-C consists of a polyfluorene backbone to which multiple tertiary amine side chains are connected via an amide group. The influence of molecular characteristics on electronic performance and morphological properties was tested and compared to that of the widely used, literature known amino-functionalized polyfluorene (PFN) and polyethylenimine (PEI). PFCON-C reduces the turn-on voltage (VON) of poly(p-phenylene vinylene) (PPV)-based OLEDs from ∼5 to ∼3 V and increases the maximum power efficiency from <2 to >5 lm W–1 compared to that of PFN. As a result of its semiconducting backbone, PFCON-C is significantly less sensitive to the processing parameters than PEI, and comparable power efficiencies are achieved for devices where thicknesses of PFCON-C are between 15 and 35 nm. Atomic force microscopy (AFM) measurements indicate that the presence of nonpolar side chains in the EIL material is important for its film-forming behavior, while Kelvin probe measurements suggest that the amount of amine groups in the side chains influences the work-function shift induced by the EIL material. These results are used to suggest strategies for the design of polymeric electron injection layers.Keywords: amino-functionalized polyfluorenes; electron injection layers; OLEDs; polyethylenimine; solution-processing;

Solution-Processed Bio-OLEDs with a Vitamin-Derived Riboflavin Tetrabutyrate Emission Layer

Co-reporter:Nils Jürgensen, Maximilian Ackermann, Tomasz Marszalek, Johannes Zimmermann, Anthony J. Morfa, Wojciech Pisula, Uwe H. F. Bunz, Felix Hinkel, and Gerardo Hernandez-Sosa

ACS Sustainable Chemistry & Engineering June 5, 2017 Volume 5(Issue 6) pp:5368-5368

Publication Date(Web):April 19, 2017

DOI:10.1021/acssuschemeng.7b00675

Solution processed biomaterials are required for the active component to develop printed biodegradable and biocompatible optoelectronic devices. Ideal film formation is crucial for the fabrication of multilayer thin film sandwich devices. We report on the characterization of thin films of the riboflavin-derived biomaterial riboflavin tetrabutyrate and its utilization in an organic light-emitting diode. We show that the nonsolution processable precursor can form homogeneous and smooth films with the addition of tailored side groups that change its solubility. We demonstrate by grazing incidence wide-angle X-ray scattering that this chemical derivative reduces the crystallinity and enhances emission, likely by suppressing π–π stacking interactions. Organic light-emitting diodes with a poly(9-vinylcarbazole)–emissive riboflavin tetrabutyrate bilayer structure yield a maximum luminance of 10 cd/m2 and external quantum efficiency of 0.02% with a 640 nm peak orange exciplex emission. External quantum efficiency measurements of a photodiode affirm the exciplex formation.Keywords: Biomaterial; Exciplex; Green electronics; Organic light-emitting diode; Organic semiconductor; Thin film;

Electron injection and interfacial trap passivation in solution-processed organic light-emitting diodes using a polymer zwitterion interlayer

Co-reporter:Marta Ruscello, Sebastian Stolz, D. Leonardo Gonzalez Arellano, Florian Ullrich, Sabina Hillebrandt, Eric Mankel, Annemarie Pucci, Wolfgang Kowalsky, Todd Emrick, Alejandro L. Briseno, Gerardo Hernandez-Sosa

Organic Electronics 2017 Volume 50(Volume 50) pp:

Publication Date(Web):1 November 2017

DOI:10.1016/j.orgel.2017.08.014

•Poly(sulfobetaine methacrylate (PSBMA) was used as electron injection layer in inverted and regular architecture OLEDs.•PSBMA layer changes the work function of the cathode depending on its thickness.•PSBMA acts as a trap passivation layer when used on ZnO cathodes, making the device more stable and better performing.Here we describe the use of a polymer zwitterion as a solution-processable material that serves as the key component of the electron injection layer (EIL) in solution processed organic light-emitting diodes (OLEDs). Poly(sulfobetaine methacrylate) (PSBMA) was employed in both regular and inverted device configurations as a work-function modifier for Al and ZnO cathodes, respectively. For both architectures, PSBMA significantly improved the OLED performance when compared to reference devices without EIL in terms of turn-on voltage and luminance. In inverted devices, PSBMA showed a passivation effect on ZnO surface trap states, producing better performing and more stable devices.Download high-res image (153KB)Download full-size image

The Swiss-Army-Knife Self-Assembled Monolayer: Improving Electron Injection, Stability, and Wettability of Metal Electrodes with a One-Minute Process

Co-reporter:Milan Alt;Malte Jesper;Janusz Schinke;Sabina Hillebrt;Patrick Reiser;Tobias Rödlmeier;Iva Angelova;Kaja Deing;Tobias Glaser;Eric Mankel;Wolfram Jaegermann;Annemarie Pucci;Uli Lemmer;U. H. F. Bunz;W. Kowalsky;G. Hernez-Sosa;R. Lovrincic;M. Hamburger

Advanced Functional Materials 2016 Volume 26( Issue 18) pp:3172-3178

Publication Date(Web):

DOI:10.1002/adfm.201505386

A novel Self-assembled Monolayer (SAM) forming molecule bisjulolidyldisulfide (9,9'-disulfanediylbis(2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinoline)) is demonstrated which lowers the work function of metal surfaces by ≈1.2 eV and can be deposited in a 1 min process. Bisjulolidyldisulfide exists in a stable disulfide configuration prior to surface exposure and can therefore be stored, handled, and processed in ambient conditions. SAM from bisjulolidyldisulfide are deposited on metal surfaces (Au and Ag), including inkjet printed Ag on polyethylene terephthalate substrates, investigated by photoelectron and infrared spectroscopy, and used as electrodes in n-type organic field effect transistor (OFET). Treatment of electrodes in OFET devices with with bisjulolidyldisulfide-SAMs reduces the contact resistance by two orders of magnitude and improves shelf life with respect to pristine metal electrodes. The presented treatment also increases the surfaces wettability and thereby facilitates solution processing of a subsequent layer. These beneficial properties for device performance, processing, and stability, combined with ease of preparation and handling, render this SAM-forming molecule an excellent candidate for the high-throughput production of flexible electronic devices.

Emissive Polyelectrolytes As Interlayer for Color Tuning and Electron Injection in Solution-Processed Light-Emitting Devices

Co-reporter:Serpil Tekoglu, Martin Petzoldt, Sebastian Stolz, Uwe H. F. Bunz, Uli Lemmer, Manuel Hamburger, and Gerardo Hernandez-Sosa

ACS Applied Materials & Interfaces 2016 Volume 8(Issue 11) pp:7320

Publication Date(Web):February 29, 2016

DOI:10.1021/acsami.6b00665

Herein we present a solution-processed hybrid device architecture combining organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) in a bilayer architecture. The LEC interlayer promotes the charge injection from an air-stable Ag cathode as well as permits the color tuning of the device emission. To this end, we used an alcohol-soluble anionic polyfluorene derivative, the properties of which were investigated by absorption and photoluminescence spectroscopy as well as by cyclic voltammetry. The bilayer device exhibited operating voltages ∼6 V and a color tuning of the emission spectrum dependent on the LEC interlayer thickness. The hybrid devices presented a color emission ranging from the yellow (x = 0.39, y = 0.47) toward the green region (x = 0.29, y = 0.4) of the Commission Internationale de I’Eclairage (CIE) 1931 chromaticity diagram.Keywords: conjugated polyelectrolyte; electron injection layer; LECs; OLEDs; polyfluorene

Poly(lactic-co-glycolic acid) (PLGA) as Ion-Conducting Polymer for Biodegradable Light-Emitting Electrochemical Cells

Co-reporter:Johannes Zimmermann, Nils Jürgensen, Anthony J. Morfa, Bohui Wang, Serpil Tekoglu, and Gerardo Hernandez-Sosa

ACS Sustainable Chemistry & Engineering 2016 Volume 4(Issue 12) pp:

Publication Date(Web):September 29, 2016

DOI:10.1021/acssuschemeng.6b01953

The use of biocompatible and biodegradable materials in optoelectronics will enable the development of promising applications in the field of healthcare and environmental sensors as well as a more sustainable production of technology. Here, we present light-emitting electrochemical cells which utilize the biodegradable polymer poly(lactic-co-glycolic acid) (PLGA) to promote ionic conductivity in the active layer of light-emitting electrochemical cells. The device performance was analyzed in terms of the volume fraction of PLGA in the active layer blend as well as with respect to three different lactic:glycolic monomer ratios (85:15, 75:25, 65:35). In all three cases, adding PLGA to the active layer leads to an improvement of the turn-on voltage of up to 2 V compared to reference devices without PLGA. This can be attributed to an increase in ionic conductivity, which was determined by impedance spectroscopy. Increasing the relative amount of PLGA in the active layer shows that the improvement is ultimately limited by poor intermixing with the polymeric emitter as observed by fluorescent microscopy. The best devices achieved turn-on voltages of 4.1 V and a maximum luminance of 3800 cd m–2 at 7.1 V.Keywords: Biodegradable; Biopolymer; Ion-conducting polymer; Light-emitting electrochemical cell; Phase separation; Solid polymer electrolyte;

Aerosol-Jet Printed Flexible Organic Photodiodes: Semi-Transparent, Color Neutral, and Highly Efficient

Co-reporter:Ralph Eckstein;Tobias Rödlmeier;Tobias Glaser;Sebastian Valouch;Ralf Mauer;Uli Lemmer;Gerardo Hernez-Sosa

Advanced Electronic Materials 2015 Volume 1( Issue 8) pp:

Publication Date(Web):

DOI:10.1002/aelm.201500101

The Compromises of Printing Organic Electronics: A Case Study of Gravure-Printed Light-Emitting Electrochemical Cells

Co-reporter:Gerardo Hernez-Sosa;Serpil Tekoglu;Sebastian Stolz;Ralph Eckstein;Claudia Teusch;Jannik Trapp;Uli Lemmer;Manuel Hamburger;Norman Mechau

Advanced Materials 2014 Volume 26( Issue 20) pp:3235-3240

Publication Date(Web):

DOI:10.1002/adma.201305541

Aerosol jet printed top grids for organic optoelectronic devices

Co-reporter:Ralph Eckstein, Gerardo Hernandez-Sosa, Uli Lemmer, Norman Mechau

Organic Electronics 2014 Volume 15(Issue 9) pp:2135-2140

Publication Date(Web):September 2014

DOI:10.1016/j.orgel.2014.05.031

•Digitally printed silver grids with 20 μm line widths fabricated on top of inverted organic solar cells.•Highly transparent (>90%) and low resistive (∼10 Ω/□) printed current collecting grids.•Significantly increased PCE by 64% due to low sheet resistance.•Ink formulation was optimized for homogeneous printing results at higher printing speeds.•Devices with printed top electrode grids have been demonstrated with 1D, 2D, and hexagonal grid layout.Aerosol jet deposited metallic grids are very promising as transparent electrodes for large area organic solar cells and organic light emitting diodes. However, the homogeneity and the printing speed remain a challenge. We report homogeneous and rapidly printed metallic lines based on a complex-based metal–organic silver ink using a processing temperature of 140 °C. We show that inhomogeneities, which are present in printed structures at increased printing speeds and mainly caused by drying effects, can be improved by adding high boiling point solvents. We demonstrate solution processed highly conductive and transparent hybrid electrodes on inverted organic solar cells comprising digitally printed top silver grids.Graphical abstract

Rheological and Drying Considerations for Uniformly Gravure-Printed Layers: Towards Large-Area Flexible Organic Light-Emitting Diodes

Co-reporter:Gerardo Hernez-Sosa;Nils Bornemann;Ingo Ringle;Michaela Agari;Edgar Dörsam;Norman Mechau;Uli Lemmer

Advanced Functional Materials 2013 Volume 23( Issue 25) pp:3164-3171

Publication Date(Web):

DOI:10.1002/adfm.201202862

Abstract

Printing organic semiconductor inks by means of roll-to-roll compatible techniques will allow a continuous, high-volume fabrication of large-area flexible optoelectronic devices. The gravure printing technique is set to become a widespread process for the high throughput fabrication of functional layers. The gravure printing process of a poly-phenylvinylene derivative light-emitting polymer dissolved in a two solvent mixture on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is studied. The surface tensions, contact angles, viscosities, and drying times of the formulations are investigated as a function of the solvent volume fraction and polymer concentration. The properties of the ink grant a homogeneous printed layer, suitable for device fabrication, when the calculated film leveling time is shorter than a critical time, at which the film has been frozen due to loss of solvent via evaporation. The knowledge obtained from the printing process is applied to fabricate organic light-emitting diodes (OLEDs) on flexible substrates, yielding a luminance of ≈5000 cd m⁻².

Gravure printed flexible small-molecule organic light emitting diodes

Co-reporter:Serpil Tekoglu, Gerardo Hernandez-Sosa, Edgar Kluge, Uli Lemmer, Norman Mechau

Organic Electronics 2013 Volume 14(Issue 12) pp:3493-3499

Publication Date(Web):December 2013

DOI:10.1016/j.orgel.2013.09.027

•Green emitting flexible SMOLEDs were fabricated by gravure printing.•The small molecule emitter was embedded in a PS matrix enabling the gravure process.•Rheological properties and drying were considered to tune the ink formulation.•Gravure printed device exhibit 67% higher efficiency than the spincoated references.Small-molecule based flexible organic light-emitting diodes (SMOLEDs) were fabricated by gravure printing. In order to modify rheological properties of the functional ink, the green emitter was embedded into an ultrahigh molecular weight polystyrene (UHMW-PS) matrix. The viscosity of the ink was characterized as a function of the small molecule:UHMW-PS weight ratio and solvent type. The gravure printed SMOLEDs exhibited a maximum luminance of 850 cd m−2, a maximum efficiency of up to 7.7 cd A−1, and turn on voltage of ∼3.5 V. The gravure printed SM:UHMW-PS device exhibits ∼67% higher luminance efficiency comparing to the spin-coated pristine SM device.Graphical abstract

The role of the polymer solid electrolyte molecular weight in light-emitting electrochemical cells

Co-reporter:Gerardo Hernandez-Sosa, Ralph Eckstein, Serpil Tekoglu, Tobias Becker, Florian Mathies, Uli Lemmer, Norman Mechau

Organic Electronics 2013 Volume 14(Issue 9) pp:2223-2227

Publication Date(Web):September 2013

DOI:10.1016/j.orgel.2013.05.040

•Light-emitting electrochemical cells were prepared using different Mw of PMMA.•The LECs solution viscosity increased in direct correlation to the PMMA Mw.•The PMMA Mw influenced the ionic conductivity and therefore Vth of the devices.•Phase separation in the thin film increased with PMMA Mw.•The best device exhibited an effective maximum luminance ∼2500 cd m−2.Different molecular weights (Mw) of poly (methyl methacrylate) (PMMA) were used as the base for the polymer solid electrolyte (PSE) in light-emitting electrochemical cells (LECs). The rheological properties of the LECs formulations are influenced by the Mw of PMMA. The Mw of PMMA also influences the PSE ionic conductivity and therefore affects the threshold voltage of the devices. Furthermore, partial segregation of the two polymers is observed, which correlates directly to the PMMA Mw. The device with the best performance was prepared with a PMMA Mw of 350,000 and exhibited an effective maximum luminance ∼3000 cd m−2.Graphical abstract

One-step additive crosslinking of conjugated polyelectrolyte interlayers: improved lifetime and performance of solution-processed OLEDs

Co-reporter:Sebastian Stolz, Martin Petzoldt, Naresh Kotadiya, Tobias Rödlmeier, Ralph Eckstein, Jan Freudenberg, Uwe H. F. Bunz, Uli Lemmer, Eric Mankel, Manuel Hamburger and Gerardo Hernandez-Sosa

Journal of Materials Chemistry A 2016 - vol. 4(Issue 47) pp:NaN11156-11156

Publication Date(Web):2016/11/08

DOI:10.1039/C6TC04417D

We crosslink an amino-functionalized polyfluorene by the solvent additive 1,8-diiodooctane (DIO). DIO remains in the film after drying of the main solvent and chemically binds to the amino-side groups after a low temperature annealing step, rendering the polyfluorene film insoluble in non-polar solvents. We correlate the amount of DIO, the reduction of operational voltage and increase in lifetime of solution-processed OLEDs. We demonstrate a fully solution-processed device using the crosslinked polyfluorene electron injection layer and an inkjet-printed Ag top electrode.