Organic light-emitting diodes made from small molecular weight organic semiconductors are composed of multiple functional layers. These layers are in most cases amorphous assemblies of the molecular building blocks. In our joint paper with our collaborators of the Group of Nanomaterials and Microsystems (GNaM) at the Universitat Autònoma de Barcelona entitled ‘High-performance organic light-emitting diodes comprising ultrastable glass layers‘, we shed some light on the growth of these layers. The work is published in Science Advances. The molecules making up the amorphous layers do not necessarily fall into place perfectly so that over time (but these are very long times beyond the lifespan of an OLED) the molecules wiggle into a more compact assembly. This settling can be accelerated greatly if the molecules on the surface are given some extra energy to migrate. Providing excess thermal energy through an elevated substrate temperature, much more stable morphologies – called ultrastable glasses – are formed. The optimum condition for this growth is around 85% of the materials glass transition temperature.
In our study we have tested this growth condition for four different phosphorescent emitters in one common device stack and found that both the external quantum efficiencies and device lifetimes significantly increased. The illustration below summarizes our work graphically.
The full citation is: J. Ràfols-Ribé, P.-A. Will, C. Hänisch, M. González-Silveira, S. Lenk, J. Rodríguez-Viejo, S. Reineke, High-performance organic light-emitting diodes comprising ultrastable glass layers. Sci. Adv. 4, eaar8332 (2018). DOI: 10.1126/sciadv.aar8332.
At this year’s SPIE Photonics Europe 2018 in Strasbourg, France, the new conference Organic Electronics and Photonics: Fundamentals and Devices (Conference 10687) will celebrate its inaugural meeting. My colleague Prof. Koen Vandewal (now at Hasselt University) and I are jointly chairing this conference.
This first conference lasts for three days (24 – 26 April 2018) and aims to concentrate the exciting and diverse research using organic materials for electronic and/or photonic applications. The conference starts on Tuesday with a full day focusing on thermally activated delayed fluorescence (TADF), followed by the Wednesday programme discussing organic photovoltaics and photodetectors as well as other optoelectronic and photonic devices, and concludes on Thursday with morning and afternoon sessions on organic light-emitting diodes.
The PHEBE consortium is well represented at this event with Prof. Andy Monkman (Durham University) giving an invited talk in the TADF Session on Tuesday with the title ‘Ultrafast reverse intersystem crossing and 100% PLQY in the same TADF molecule, really!’ followed by another contribution from the PHEBE consortium about white OLEDs using blue TADF emitters by Ludwig Popp et al. (TU Dresden and Kaunas University of Technology) ‘Warm-white hybrid emission from TADF and phosphorescence and its application in OLEDs’. The conference is co-organized by the PHEBE member Prof. Sebastian Reineke.
Many experts in the field of OLEDs and TADF, including Wolfgang Brütting, Reinder Coehoorn, Vladimir Dyakonov, Franky So, Seunghyup Yoo, Eli Zysman-Coleman, will be presenting their newest results. With Cynora GmbH and Osram OLED GmbH, leading European companies working on OLEDs will be also represented at the conference.
To register for this event, please visit http://spie.org/conferences-and-exhibitions/photonics-europe
The conference Organic Light Emitting Materials and Devices (OP212) goes into its 22nd round (XXII) this year at the SPIE Optics+Photonics 2018 in San Diego. The abstracts for contributions are due February 7, 2018 – so a couple of weeks to go. Don’t miss out this excellent opportunity to showcase your latest research results. A pdf version of the Call for Papers can be downloaded here: OP18P OP212 Call Flyer.
The abstract submission deadline for the upcoming SPIE Photonics Europe 2018 (April 22-26, 2018) in Strasbourg, France, is closing in: October 23, 2017, so only 3 days to go!
My colleague Koen Vandewal and I organize the new Conference Organic Electronics and Photonics: Fundamentals and Devices (EPE117).
We are inviting everyone working in the field of organic electronics and photonics to consider our Conference and to submit an abstract. We are looking forward to a broad, state-of-the-art exchange of research and development trends.
Please do also spread the word, if you know colleagues of yours, who might be interested to go.
In this paper entitled ‘Transparent and color-tunable organic light-emitting diodes with highly balanced emission to both sides‘ we demonstrate transparent, two-color, stacked OLEDs that allow for balanced top- and bottom-emission. Making use of ultra thin, composite metal electrodes, this design avoids the use of ITO, such that this architecture can be transferred to flexible substrates. Careful optical design made it possible that the luminance of the device is virtually identical to both viewing directions, which is a great improvement over many earlier device layouts.
Our new paper entitled “Adjustable white-light emission from a photo-structured micro-OLED array” published in Light: Science & Applications discusses an approach towards micro-OLED arrays made of differently emitting sub pixels without non-emissive areas. This is achieved using orthogonal lithography techniques in a way that only the first OLED unit is structured while the next one to follow is made in a “fill-the-gap” approach. In this conceptual demonstration, we pair blue and yellow OLEDs in a stripe layout, which can be addressed individually for complete color tunability. Feature sizes of the stripes are down to 20 micrometer.
Its the last day of MRS Spring 2016 and still we are by far not done with our Symposium EP1: Organic Excitonic Systems and Devices. We have a full day of oral presentations split into two major sessions.
EP1.7: Advanced Organic Devices and Modeling
As the title indicates, some new concepts for devices based on organic materials will be central in this session. This is complemented by some efforts on modeling. Keywords for this session are:
- Stretchable electronic structures
- Modeling exciton and polaron dynamics for transient EL in OLEDs
- Nanoscale electrical inhomogeneities in OLEDs
- Visible light communications with organic systems
- Method to predict interface barriers in OLED layers
- Rare-earth up-conversion composites for PV
Our invited speaker in the morning is Graham A. Turnbull. Note: Franky So was not able to come to Phoenix, so that his presentation is cancelled. Klaus Meerholz had his talk already late last night.
EP1.8: Excitonic Charge Transfer States
Our final look in this last session is on charge transfer states and related phenomena. Most naturally, this is the time, where we will have presentations that are closer to photovoltaic properties than in the days before. Actually, this session closes the loop to the first sessions of the week, where we were guided a lot by internal charge transfer states in TADF materials.
Here are some details to the post-lunch session:
- Enhancing exciton dissociation rates at heterojunctions using FRET
- CT state transport at donor-acceptor blends
- Magnetic field modulation of exciton recombination
- Tailoring interfaces using additive engineering
- Generation and modulation of chi^2 optical non-linearities
- Printing highly efficient solution processed solar cells
- Multiple CT states in ordered and disordered systems
Max Shtein will be our invited speaker of the afternoon session.
See you around!