Due to the cancellation of many scientific conferences, the AUCAOS committee is pleased to host online seminars on the first Wednesday of every month until normal conferences can resume.
Screen recordings of past seminars are available to view below.
Wednesday 5 August 2020
1:00 - 1:25pm AEST
Characterising the Interface and Dipole in Organic-based Photovoltaics
Dr. Yanting Yin
A combination of electron spectroscopy and ion scattering spectroscopy has been carried out to directly characterize the chemical and electrical properties at the interface formed with high workfunction (WF) hole transport layer-MoO3 and conjugate polymer. Characterization of chemical features and concentration distribution on a P3HT:PC61BM bulk-heterojuction (BHJ) with MoO3 arises an observation of energy shift of BHJ and diffusion of MoO3. The dipole formation at such interface can be indicated. Gradual changes upon electronic structure such as WF and valence electron states were observed from the analysis. A decomposition algorithm introduced in the work yields an insight into the dipole strength thus the complete energy level positioning at the interface can be restored. The mechanism of charge transport over the MoO3/BHJ interface was thus discussed with the determination of dipole strength maximizing at 2.1eV. A similar characterization upon interface was studied upon the growth of thermal-evaporated LiF on polymer BHJ. Further investigation has been made of the interface with a simulation of common contamination such as air exposure, and commercialized fabrication process such as thermal annealing consequence during fabrication. The results show that, the electronic properties of the original interface can be altered once the structure was subjected to contamination and thermal treatment. The analysis offers an insight of device performance of solar cells correlated to interface dipole features.
1:25 - 1:50pm AEST
Red Emission from Nature Inspired Bay-Annulated Indigo Derivatives
Ms Nicholle Wallwork 1,2
University of Queensland
Atul Shukla,1,3 Xin Li,1,2 Jan Sobus,1,3 Van T. N. Mai,1,2 Sarah K. M. McGregor,1,2 Kay Chen,2 Romain J. Lepage,2 Elizabeth H. Krenske,2 Evan G. Moore,2 M. Mamada,4 C. Adachi,4,* Ebinazar B. Namdas,1,3* Shih-Chun Lo1,2*
1. Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, Queensland, 4072, Australia
2. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072, Queensland, Australia
3. School of Mathematics and Physics, The University of Queensland, Queensland, Brisbane, Queensland, 4072, Australia
4. Centre for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan
Organic semiconductor materials offer high mechanical flexibility and high wavelength-tunability, which have great potential as a complementary technology to current inorganic lasers, particularly for spectroscopy, sensing, optical data communication, display, and security tag applications.1 Recent research efforts on organic semiconductor lasers have demonstrated notable organic semiconductor materials possessing both high optical gain and low amplified spontaneous emission (ASE) thresholds in blue and green colours.2 However, the same progress has not been made on red laser dyes mainly due to their low photoluminescence quantum yields (PLQYs) recognised as the "energy bandgap law" for low-energy emission. To overcome this, in this presentation our development of a new family of solution-processable organic semiconductor laser dyes with deep-red emission, high thermal stability and high PLQYs (≈100%) will be shown. Our strategies in achieving low film ASE thresholds (9.6 μJ/cm2 at 650 nm), low laser thresholds (6 μJ/cm2) and high stability under optical pumping (retained 90% of the initial output even after (≈9,600 pump pulses of continuous pumping at 20 Hz) will be further discussed.3 Finally, our preliminary work on TADF-Assistant Fluorescent OLEDs (TAF-OLEDs)4 based on the new red laser dyes will be demonstrated to show high promise as a new family of organic semiconductor materials.
1. A. J. C. Kuehne, M. C. Gather., Chem. Rev. 2016, 116, 12823.
2. T. N. V. Mai, A. Shukla, M. Mamada, S. Maedera, P. E. Shaw, J. Sobus, I. Allison, C. Adachi, E. B. Namdas, S.-C. Lo, ACS Photonics 2018, 5, 4447; Y. Oyama, M. Mamada, A. Shukla, E. G. Moore, S.-C. Lo, E. B. Namdas, C. Adachi, ACS Mater. Lett. 2020, 21, 161.
3. A. Shukla, N. R. Wallwork, X. Li, J. Sobas, V. T. N. Mai, S. K. M. McGregor, K. Chen, R. J. Lepage, E. H. Krenske, E. G. Moore, E. B. Namdas, S.-C. Lo, Adv. Opt. Mater. 2020, 8, 1901350.
4. H. Nakanotani, T. Higuchi, T. Furukawa, K. Masui, K. Morimoto, M. Numata, H. Tanaka, Y. Sagara, T. Yasuda, C. Adachi, Nature Commun. 2014, 5, 4016.
Acknowledgement: We thank Australian Research Council (DP160100700 and DP180103047), and Department of Industry, Innovation and Science (AISRF53765), and Japan Society for the Promotion of Science (JSPS Core-to-Core 18050011-000441) for financial support.
Thursday 2 July 2020
1:00 - 1:25pm AEST
Hybrid organic/inorganic chromophores
Dr Nathaniel Davis
Victoria University of Wellington
Luminescent light harvesting chromophores have the potential to improve many optoelectronic technologies, such as photovoltaics, LEDS, lasers and luminescent solar concentrators. Our research into the creation of artificial light-harvesting antenna complexes aims to disrupt the current chromophore technology. The current state of the art chromophores can be split into two types: 1) Organics, which suffer heavily from instability and reabsorption; and 2) Inorganics, which solved many of the problems inherent with organic emitters in terms of stability and reabsorption but require complex surface treatments to improve their luminescent efficiency (LE). We aim to combine the beneficial properties of both these systems into a single hybrid chromophore. This will act to improve the LE of the hybrid particle and reduce reabsorption losses. The science behind attaching chromophores to nanocrystals and studying the subsequent photophysics is in its infancy. We envision two options forward, that would promote the field, both based on the replacement of ligands on a nanocrystal that offer colloidal stability with ones that add additional optoelectronic properties. 1) Energy transfer from the ligand into the nanocrystal, which will have potential applications for increased solar absorption, efficient transport of excitations, and singlet fission. 2) Coupling a highly luminescent molecule to a nanocrystal, avoids the complex surface passivations (treatments) required by current state-the-art nontoxic emitters and offers the potential for upconversion of light.This talk will look at our recent success with caesium lead halide nanocrystals.
1:25 - 1:50pm AEST
Dicyanovinyl-based fluorescent sensors for dual mechanism amine sensing
Dr. Guanran Zhang
University of Queensland
Food wastage due to spoiling is a global economic issue and contributes to over-farming and overfishing with real environmental consequences. Smart food packaging is a promising solution to this problem, the idea of which is to utilize responsive sensors that allow direct monitoring of the gasses released from food as it spoils and provides a visual indicator to the consumer. Here we report two dicyanovinyl-fluorene-benzothiadiazole-based fluorescent compounds, K12 and K12b, both of which showed rapid response to biogenic amines via two independent mechanisms. When primary alkyl amines were present in solution, they underwent Michael addition with the dicyanovinyl group of the sensing material, resulting in rapid color change. The reaction products of K12 and K12b with primary amines also showed a decrease and increase in the fluorescence quantum yield, respectively, enabling a unique dual-sensor array with turn-off/turn-on response. In addition, fluorescence quenching via photoinduced hole transfer was observed in the solid-state sensor films with a wide range of primary, secondary and tertiary amines, enabling rapid and sensitive detection of amine vapors. Finally, as a proof-of-concept integrated packaging sensor, soft membranes incorporating K12 and K12b were prepared and showed rapid response to primary amine vapor.
Thursday 4 June 2020
1:00 - 1:25pm AEST
An introduction into synthetic molecular motors
Dr Jos Kistemaker
The University of Queensland
Scientific advances made in the last three decades, inspired by Nature's example, has led to a diverse collection of synthetic molecular machinery. A prominent example of this machinery is the molecular motor developed by Feringa and co-workers which is based on a light driven overcrowded alkene. The study of several generations of molecular motors and their properties have had primarily academic merit, however, later developments have shown that these nanomachines can be used to do actual work and might prove to be the driving force in the transition to actual applications.
This talk will provide an introduction into the field of synthetic molecular motors with an emphasis on light driven rotary motors. The role of autonomy and chirality in different designs will be highlighted and several examples will be used to showcase the expression and translation of these features to other groups, molecules and larger scales.
1:25 - 1:50pm AEST
Electronic coupling: A significant contributor to electron transfer between similarly structured surface-bound porphyrins and Co2+/3+ complex electrolytes
Mr Inseong Cho
University of Wollongong
Electronic coupling is often assumed to play a minor role in interfacial electron transfer (ET) between similarly structured electron donors and acceptors. To check this assumption, we investigated the ET kinetics between four surface-bound free-base and Zn porphyrins and five Co2+/3+ complexes redox mediators with different ligands using transient absorption spectroscopy (TAS). The ET rates measured in this work are the fastest reported in the literature for surface-bound molecules and donors dissolved in electrolytes. By using a novel sub-ns TA setup, the importance of enhanced TAS time-resolution is demonstrated. Fitting the measured ET rate versus -ΔG resulted in poor fits with unrealistic trends in reorganisation energy values. This is explained by up to 60% variation of the electronic coupling (HDA) depending on the size of the alkyl-substituent of the Co2+/3+ complexes redox mediator. The HDA values obtained by assuming a constant reorganisation energy are shown to be dependent on tunnelling distances, characterised by tunnelling attenuation factor βel = 0.16 to 2.0 Å-1. This work suggests that changes in electronic coupling even by small structural modification previously considered negligible can be as significant as the effect of driving force.
Thursday 7 May 2020
1:00 - 1:25pm AEST
Microstructure formation in solution-processed semiconducting polymer thin films
Prof. Chris McNeill
Semiconducting polymers are interesting materials that are being developed for a wide range of applications including polymer field-effect transistors, polymer solar cells, and polymer light emitting diodes. The performance of such devices is strongly dependent upon the thin film microstructure of the active semiconducting polymer thin film. As semiconducting polymers are processed from solution, the resulting thin film microstructure is complicated and can be hard to control. In this presentation I will present research performed in my group aimed at understanding how microstructure forms in solution-processed semiconducting polymer thin films. A focus will be placed on the n-type naphthalene dimide-based polymer P(NDI2OD-T2) which exhibits a rich microstructure and good performance in field-effect transistors and polymer solar cells. The influence of molecular weight and processing conditions on thin film microstructure will be discussed, along with the impact of thin film microstructure on field-effect transistor performance. This talk will also feature a host of different synchrotron-based techniques that have been used to understand the polymer physics and microstructure of this system.
1:25 - 1:50pm AEST
Charge transport in disordered materials for photodetector applications
Dr. Almantas Pivrikas
Non-crystalline disordered semiconductors such as organic molecules, polymers, nanoparticles offer great advantage for electronic devices where the novel physics as well is yet to uncovered. All these materials lack long range structural order and have one common feature - their electrical conduction is inferior compared to highly-crystalline inorganic semiconductors such as silicon because of orders of magnitude lower electron and hole mobilities as well as strong recombination rates. Yet, organic electronic devices made using these disordered materials have the performance comparable to their classical inorganic counterparts. Photoconductivity and charge transport measurement techniques such as Time-of-Flight or Hall-effect are typically not applicable or unreliable to study the charge transport in these disordered systems. In this presentation the core problems with experimental issues will be explained and our novel techniques introduced. Our work relating to hot photocarrier utilization in photodetectors as well as the novel peculiarities of charge carrier recombination in crystalline and disordered semiconductors will be demonstrated.