9:00 - 9:25InvitedID: 277
EXCITON AND CHARGE DIFFUSION IN ORGANIC AND HYBRID SEMICONDUCTORS
Organic Semiconductor Centre, School of Physics and Astronomy, University of St Andrews, St Andrews, United Kingdom
The diffusion of charges and excitons is very important in a wide range of optoelectronic
devices, especially solar cells. In hybrid perovskites, the absorption of light generates
charges which diffuse to the interface with the contact layers. In organic solar cells, light
generates excitons which then diffuse to an acceptor. We will show how in both cases time-
resolved spectroscopy is a powerful technique for the study of these processes and gives
important insight into device design and operation. We use similar techniques – for
example surface quenching – to study exciton or charge diffusion. We report a study
comparing CH 3 NH 3 PbI3 on PEDOT:PSS and on NiO. Carrier extraction involves both
transport across the active layer and transfer at the interface to the hole extraction layer.
We find that hole diffusion is very fast (diffusion coefficient ~2 cm 2 /Vs) but that PEDOT:PSS
limits the overall extraction rate. In contrast NiO enables faster charge extraction.
9:25 - 9:50InvitedID: 248
A NEW APPROACH TO SUPER-RESOLUTION SPECTROSCOPY
1Institute of Integrative Biology of the Cell, Gif sur Yvette, France; 2Center for Physical Sciences and Technology, Vilnius, Lithuania
We have developed a new approach to super-resolution fluorescence spectroscopy, based on the use of a detector smaller than the diffrraction-limited image of a point emitter. With such a small detector, classical scaning microscopy acquires super-resolution.
This method, entirely based on geometric optics, allows super-resolution images to be recorded from any type of fluorophore, and allows images from autofluorescent samples to be recorded at resolution higher than 100 nm.
Examples of the use of this method in biology, showing the amazing axial and lateral resolution of the method as well as its wide potential use, will be displayed.
This approach can be used not only in fluorescence, but also in any diffusion method, as well as in transmission, leading in the near future to the first super-resolution transmission microscope.
9:50 - 10:15InvitedID: 228
FEATURES AND FATES OF EXCITONS IN LUMINESCENT ORGANIC SOLIDS
IMDEA Nanoscience, Madrid, Spain
The last years have seen a boost in small molecule based conjugated materials for innovative (opto)electronic applications. Targeted design of such materials requires nevertheless a systematic understanding of structure-property relationships; this however can only be achieved if all intra- and intermolecular parameters are controlled. We are therefore systematically investigating luminescent single crystals and nanoparticles by integrating optical spectroscopy and quantum chemistry to unveil features and fates of molecular excitons when going from solution to the solid state. Our studies give detailed insight in the conditions for effective & color-tuned spontaneous and stimulated light emission, stressing the cooperative effect of molecular properties, intermolecular arrangement and morphology.
 Solid State Luminescence Enhancement in p-Conjugated Materials: Unraveling the Mechanism beyond the Framework of AIE/AIEE. J. Shi et al, J. Gierschner, J. Phys. Chem. C 121 (2017) 23166.
 Twist Elasticity Controlled Crystal Emission in Highly Luminescent Polymorphs of Cyano-Substituted Distyrylbenzene (bDCS). J. Shi et al, J. Gierschner, Adv. Opt. Mater. 5 (2017) 1700340.
 Organic Single Crystal Lasers - a Materials View. J. Gierschner et al, Adv. Opt. Mater. 4 (2016) 348.
 Luminescent Distyrylbenzenes: Tailoring Molecular Structure and Crystalline Morphology. J. Gierschner, S. Y. Park, J. Mater. Chem. C 1 (2013) 5818–5832.
 Highly Emissive H-Aggregates or Aggregation-Induced Emission Quenching? The Photophysics of All-Trans Para-Distyrylbenzene. J. Gierschner et al, J. Phys. Chem. Lett. 4 (2013) 2686.
10:15 - 10:30ID: 175
CROSSED 2D VS. SLIPPED 1D PI-STACKING IN POLYMORPHS OF CRYSTALLINE ORGANIC THIN FILMS: IMPACT ON THE ELECTRONIC AND OPTICAL RESPONSE
1University of Valencia, Burjassot (Valencia), Spain; 2Institute of Solid State Physics, Graz University of Technology, Graz, Austria; 3Madrid Institute for Advanced Studies, IMDEA Nanoscience, Madrid, Spain; 4Center for Supramolecular Optoelectronic Materials, Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea; 5Laboratory for Chemistry of Novel Materials, Université de Mons, Mons, Belgium; 6Elettra-Sincrotrone Trieste, AREA Science Park, Basovizza, Trieste, Italy
The device functionality of small molecule-based organic optoelectronics depends strongly on the intermolecular arrangements and on morphological factors. This becomes apparent if the optical or electric response of different polymorphs of the same materials are considered. In particular, 2D arrangements – gathered via edge-to-face (herringbone) or slipped face-to-face (brickwork) packing motifs - were early realized as advantageous for efficient charge transport.
Here, we report on the successful x-ray diffraction structure analysis of two polymorphic phases (B, G) of a dicyano-distyrylbenzene derivative, being a crucial step for the understanding of the electronic and optical response of the final devices. B- and G-phase show dramatically different molecular 2D crossed π-stack vs. 1D slipped π-stack packing motifs. The drastically different device functionalities, i.e. the (anisotropic) electronic and optical response, are fully elucidated by means of (time-dependent) density functional theory, (TD)DFT, being all together a crucial step towards future device analysis of novel third generation organic optoelectronic materials.
10:30 - 10:55InvitedID: 281
CAN EXCIPLEX DIFFUSE?
Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea
Excited-state charge-transfer complexes (exciplexes) play very important roles in organic photonic devices such as organic light emitting diodes or organic photovoltaics as intermediate for triplet harvesting using fluorescent molecules or for charge generation, respectively, so that they eventually act as a key factor determining the device performance. However, their movement or diffusion has been neglected despite its influence on device performance due to the lack of apparent charge-transfer absorption. Here, we clearly demonstrate, based on the analysis of transient photo-luminescence, that the exciplexes move via energy transfers (ETs) from exciplex donors to exciplex acceptors and the ETs takes place via the Dexter mechanism.