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!
Tomorrow, Wednesday March 30, we have two sessions at our Symposium EP1: Organic Excitonic Systems and Devices.
EP1.2: Organic Emitters
The morning focus will be on the emitters itself, where we will here recent progress on various molecular concepts for high performance luminescence. This will include the fundamental studies that excel our current understanding of these emitters. Some things that we will see:
- Design rules for TADF emitters
- Crystalline OLED emission layers for nearly perfect emitter alignment
- Investigation of exciplex emission (electric field dependence and charge separation)
- Nickel-Tetra-Mesityl-Porphoyrin photophysics
- Platinum complexes for high efficiency, color pure blue OLEDs
- Control of molecular orientation
- TADF emitters for LECs and OLEDs
- Biluminescence for optical sensing
- Photophysics of H- and J-aggregates
Our invited speakers of the morning are: Andrew Monkman, Wolfgang Brütting, and Frank Würthner.
EP1.3: Organic Lasers
In the afternoon we switch gears – Its laser time. With the basis of the laser tutorial we had on Monday, we should be all set for some interesting contributions related to laser physics with organics. Important: Due to a serious illness of one of our speakers, the program of the first part of the EP1.3 session has been updated. We will start at 2:00pm rather than the originally planned time of 1:30pm. Please refer to the online program for the latest updates!
Here are some details to the post-lunch session:
- Condensate physics with organic polaritons
- Tunable, narrow line width solid-state lasers
- LED-pumped organic lasers (planar integration) based on luminescent concentration
- Self-assembled colloidal lasers
- Low threshold up-converted laser
- Strong coupling in organic microcavities
- Solvent nano imprint lithography of polymer lasers
- Photoluminescence enhancement in nano cavities
Our afternoon invited speakers are: Stéphane Kéna-Cohen and Alexander J. Kuehne.
Again, a lot of cool and interesting things to look forward to. See you tomorrow!
Tomorrow, Tuesday March 29, we start out with the first Session of our Symposium EP1 Organic Excitonic Systems and Devices. The session runs under the title Organic Light-Emitting Devices (OLEDs). So clearly, we are looking to a collection of recent progress on the OLED technology, where the optimization of efficiency is in the central focus. Here are some keywords that will represent the content of tomorrow:
- Enhanced emission of OLEDs
- Bright NIR OLEDs based on high mobility polymers
- Intrinsic degradation mechanisms in UV and blue OLEDs
- Increased stability of TADF OLEDs
- 100% triplet harvesting in fluorescent OLEDs
- Blue phosphorescent OLEDs
- Absence of triplet up-conversion in anthracene based emitters
- Afterglow OLEDs (a demonstration of biluminescence in OLEDs)
- Origin and control of emitter orientation in OLEDs
Our invited speakers for this session are: Mark Thompson, Stephen R. Forrest, and Jang-Joo Kim.
A couple of impressions from our tutorial connected to the MRS Spring 2016 Symposium EP1: Organic Excitonic Materials and Devices: In short, the room has been packed with more attendees than chairs in the room. Chihaya Adachi started out giving us a complete overview on a class of materials for organic light-emitting diodes, he pioneered, namely thermally activated delayed fluorescence (TADF)-type emitters. He reflected on his initial reports on TADF in 2009, when nobody in the community cared about this concept, lacking competitive efficiency values at the time. Nowadays, these materials are TADF on par with phosphorescence in respect to device efficiency. Listening between the lines, we learned that up to date, the Adachi Lab counts more than 200 TADF molecules made – impressive.
After very limited coffee supply during the break, Stéphane Kéna-Cohan switched gears and gave us a very insightful introduction to the world of organic based lasers. Beginning with the very basics needed for understanding the concepts of lasers in general, we ended up learning the very current developments connected with laser research based on organic materials. The key potential here is seen for its high degree of possible integration, which is for instance important for bio-applications. When discussing the challenges remaining towards the demonstration of an electrically pumped organic laser, Stéphane Kéna-Cohan motivated where the threshold for electrical pumping roughly is using a back-on-an-envelope calculation, which actually fits on an envelope, as the picture below proves.
With the tutorial done, we are looking forward to the upcoming four days of regular symposium program. The sessions will reconvene at a different room: PCC North, 200 Level, Room 227 A. See you tomorrow.
Finally, the first ever MRS Spring Meeting in Phoenix, Arizona, is here in 2016. It runs from March 28 to April 1. My colleagues Malte C. Gather, Marc A. Baldo, Chihaya Adachi and I are excited to participate in this event with the Symposium EP1: Organic Excitonic Materials and Devices. We are looking forward to a full week of a packed, interesting, and diverse program.
But before the symposium even starts, we have a tutorial to offer: Tutorial EP1: Organic Excitonic Materials and Devices – OLEDs and Lasers. It will run tomorrow, Monday March 28 from 8:30 am to 12 pm. Location is PCC North, 100 Level, Room 125 B.
We are happy to have Chihaya Adachi (Kyushu University) and Stéphane Kéna-Cohen (Ècole Polytechnique de Montréal) as instructors for the tutorial on board. We will hear in-depth introductions to OLEDs and Lasers, respectively. Come and join us tomorrow to kick-off our Symposium EP1 early with this half-day tutorial session. Here are the details:
Part I: Chihaya Adachi
The first segment will discuss the key properties of organic molecules important for the use in electroluminescent devices, i.e., organic light-emitting diodes (OLEDs). The fact that about 75% of the excitons are formed in an energetically distinct, nonradiative triplet state urges materials designers to come up with innovative solutions. There will be a detailed discussion of a very recent excitonic scheme: thermally activated delayed fluorescence (TADF), which Professor Adachi and his research team recently pioneered.
Part II: Stéphane Kéna-Cohen
This segment will begin with a review of basic laser physics in the context of organic lasers, briefly surveying state-of-the-art organic lasers and their applications. Electrically pumped organic lasing remains one of the open challenges in the field of organic electronics and the main difficulties toward achieving this goal will be discussed. The second half will cover a new type of laser, dubbed a polariton laser, which has the potential to drastically lower organic laser thresholds. The physics behind such polaritons will be discussed and some of the fascinating physics that have been observed (ballistic propagation, spontaneous vortices, superfluidity) will be described.
See you tomorrow!