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!
This afternoon, we are progressing with the general scheme of topics with the session EP1.5 Excitons in Organic and Hybrid Systems II of our Symposium EP1. Important: We have one additional speaker in the afternoon: Klaus Meerholz – his talk got shifted from Friday to this session. The following topics we will see:
- NIR EL from surface plasmons
- Area light-emitting transistors
- Multiple FRET pathways
- Topological phases in organic materials
- Manipulating Excitons with plasmonic nanoantennas
- Singlet exciton fission
- Real time exciton diffusion mapping
- Organic memory devices
Our invited speakers for the afternoon are Jana Zaumseil, Joel Yuen-Zhou, Gleb M. Akselrod, and Klaus Meerholz.
See you in a bit!
This announcement comes in parallel with the start of the session Excitons in Organic and Hybrid Systems I of our Symposium EP1, which began 5 minutes ago. Today we are looking in more detail on processes connected with excitons in organic and hybrid systems. We will see sophisticated techniques, modeling, etc.
Here are some keywords that we will come across during the morning program:
- Nanoscale exciton migration
- QM/MM simulation of TADF materials
- Exciton migration in TADF materials
- Exciton transport in colloidal QDs
- Spin oscillations
- Single molecule look on TADF
- Spatial confinement of triplet excitons in rubrene
- Exciton processes in OLEDs
Our invitees are Naomi Ginsberg, William Tisdale, John Lupton, and Grayson Ingram.
In a new paper – Spin-dependent charge transfer state design rules in organic photovoltaics – published in Nature Communications, we probe intermolecular charge transfer states with the aid of their luminescent thermally activated delayed fluorescence (TADF) channel. In addition to probing this TADF with time-resolved photoluminescence alone, we examine the dynamics of the system under a variation of the electron and hole spacing of the CT states, controlled through external pressure. The comparison of two different acceptor molecules with either low or high local triplet energies directly shows the significance of the careful energetic design of charge separating interface in organic photovoltaics. Here, a low lying triplet level on the acceptor significantly quenches the CT triplet states, increasing the overall recombination losses.
In my last post, I highlighted our most recent publication in Scientific Reports, which discusses novel strategies to achieve room temperature phosphorescence of organic semiconductors by means of sample engineering and exciton management (see: ‘Room temperature triplet state spectroscopy of organic semiconductors‘). In today’s post, I’d like to give some very convincing evidence, how well these approaches work out in real time and space.
In the video below, you see a couple of glass slides that are covered with a thin film composed of the polymer PMMA [Poly(methyl 2-methylpropenoate)], into which 2 wt% of the well known organic material NPB [N,N′-di(naphtha-1-yl)-N,N′-diphenyl-benzidine] is embedded. The sample is optically excited with a 365 nm LED, giving rise to blue fluorescence of NPB. Whenever the LED is turned off, the sample shows a persistent emission of green/yellow color, which is the phosphorescence of NPB. Conditions: room temperature, nitrogen atmosphere.
Organic electronic devices such as solar cells and light-emitting diodes convert between photons and charges (and vice versa) via intermediate, localized states: the excitons. It is the localized nature of the fundamental electronic excitation of organic semiconductors that make them prone to bimolecular annihilation processes. In this paper, Nanostructured Singlet Fission Photovoltaics Subject to Triplet-Charge Annihilation, we investigate the interaction between triplet excitons and charges (or more precisely polarons) in archetypical, state-of-the-art singlet fission photovoltaic cells. This understanding is crucial because singlet fission, capable of generating multiple excitons per incident photon, solely relies on the formation and consecutive dissociation of long-lived, dark triplet excitons.