Online Seminar Announcement: Wednesday 5 August 2020

Dr. Yanting Yin
Flinders University

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.

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 Lo^1,2*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.

References: 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.