Online Seminar Announcement: Wednesday 3 November 2021

Wednesday 3 November 2021

High Efficiency Deep Blue OLEDs

Jang-Joo Kim

Seoul National University, Korea
JooAm Co.

Time: 1pm in QLD 2pm in NSW, ACT, Vic, and Tas

11am in WA

12:30pm in NT

1:30pm in SA

4pm in New Zealand

Meeting URL: https://jcu.zoom.us/j/83099059507

The efficiency of organic light emitting diodes has been significantly improved during the last several years by developing phosphorescent and TADF emitters with high horizontal emitting dipole orientation and high PLQY along with the development of device structure with excellent charge balance to get EQE reaching almost 40%, corresponding to almost the theoretical limit of the efficiency. The most important remaining issue is the development of deep blue OLEDs. In this talk, we will firstly present a theoretical model to analyze the degradation mechanism of OLEDs and application of the model to blue OLEDs. Then we will talk about a strategy to realize deep blue TADF OLEDs with the EQE of 28% and CIE y value of 0.09 by narrowing the emission spectrum of blue emitting TADF emitters along with high horizontal emitting dipole orientation. Lastly, we will discuss on deep blue OLEDs utilizing triplet-triplet annihilation (TTA) process based on anthracene derivatives. For blue-emitting anthracene derivatives, the theoretical maximum contribution of TTA to emissive singlet excitons is 15%, which is insufficient for high-efficiency fluorescent devices. In this study, we realised a TTA contribution of nearly 25% using an anthracene derivative, breaking the theoretical limit. As a result, efficient deep-blue TTA fluorescent devices were developed, which exhibited maximum external quantum efficiencies of 10.2%. A theoretical model will be presented to explain the experimental results considering both the TTA and RISC to a singlet state from a high level triplet state formed by the TTA process.

During the seminar:

• Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.

• You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.

• If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars:

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts:

Seminars are typically held on the first Wednesday of each month.

At this time we are specifically encouraging HDR students to present their work to broad audience. If you are interested in speaking then please submit an abstract to bronson.philippa@jcu.edu.au.


Online Seminar Announcement: Wednesday 6 October 2021

Wednesday 6 October 2021

Time: 1pm in QLD 2pm in NSW, ACT, Vic, and Tas

11am in WA

12:30pm in NT

1:30pm in SA

4pm in New Zealand

Meeting URL:https://jcu.zoom.us/j/81696511133

Seminar schedule

Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed)

Presentation
1:00 – 1:25pm

Rivers of light – ternary exciplex blends for high efficiency solution-processed red phosphorescent organic light emitting diodes

Jaber Saghaei,1 Steven M. Russell,1 Hui Jin,1 Paul L. Burn,1* Almantas Pivrikas2, Paul E. Shaw1

1Centre for Organic Photonics & Electronics (COPE), School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia
2School of Engineering and Information Technology, Murdoch University, Perth, Western Australia, 6150, Australia
* p.burn2@uq.edu.au

Red-emitting organic light-emitting diodes (OLEDs) are important for displays and lighting, with the latter benefiting from solution processable materials, which would enable low embedded energy, scalable fabrication. Herein we describe the effect of annealing and phase separation on the performance of solution-processed OLEDs incorporating a light emitting layer composed of the exciplex host, m-MTDATA:OXD-7, and a red phosphorescent light-emitting dendrimer, Ir(tDCpq)3. Solution-processed OLEDs containing an annealed emissive layer with a low dendrimer concentration (2 wt%) were found to have the best performance, which was higher than the device in which the light emitting layer was not annealed. The improvement in performance of the annealed device was ascribed to improved charge mobility within the emissive layer caused by phase separation of the OXD-7. The OLEDs containing annealed m-MTDATA:OXD-7:(2 wt%) Ir(tDCpq)3 had maximum current, power and external quantum efficiencies of 17.9 cd/A, 19.4 lm/W, and 14.8±0.6%, respectively. The fact that the maximum EQE of 14.8% was larger than that expected based on the PLQY and the normal out-coupling efficiency of 20% from a bottom-emitting devices was determined to arise from the different pathways of exciton formation under photoexcitation and charge injection.

 

 


During the seminar:

• Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.

• You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.

• If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars:

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts:

Seminars are typically held on the first Wednesday of each month.

At this time we are specifically encouraging HDR students to present their work to broad audience. If you are interested in speaking then please submit an abstract to bronson.philippa@jcu.edu.au.


Online Seminar Announcement: Wednesday 1 September 2021

Wednesday 1 September 2021

Time: 1pm in QLD, NSW, ACT, Vic, and Tas

11am in WA 12:30pm in NT

12:30pm in SA

3pm in New Zealand

Meeting URL: https://jcu.zoom.us/j/83033425738

Seminar schedule

Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed)

Presentation
1:00 – 1:25pm

Understanding the formation and morphology of organic semiconductor thin films at the atomic level

Audrey V. Sanzogni

The University of Queensland

Functional thin films composed of organic semiconductors are transforming opto-electronic devices ranging from light weight flexible solar cells, lighting and displays to the latest in low-cost tuneable sensor materials. The key active layers in these devices are not only amorphous but often only tens of nanometre thick meaning the morphology of the material is dominated by interfacial effects and the properties of the materials depend not only on the chemical composition, but the manner of deposition and post-manufacturing processes. Furthermore, while experimental studies on amorphous systems can provide information on bulk or averaged properties, the performance of a specific device in terms of efficiency and life-time are often dominated by variations in the local morphology. To advance the utility of organic thin film devices, we need to understand how morphology relates to performance in atomic detail.
In my talk I will show how atomistic molecular dynamics simulations in which different manufacturing processes such as vacuum deposition1 and solution processing2 are reproduced in detail are providing novel insights into how morphology affects the performance of real devices. The predictive power of these models will be demonstrated as well as how elements such as the aggregation of guest molecules in a host matrix and the potential of solvent remaining in a thin film after solution deposition (Figure 1) are providing key insights into the function and properties of organic thin films.

Figure 1: Snapshots of a solution processing simulation over time and the resulting thin film

1. Lee, T.; Sanzogni, A.; Zhangzhou, N.; Burn, P. L.; Mark, A. E., Morphology of a Bulk Heterojunction Photovoltaic Cell with Low Donor Concentration. ACS Appl. Mater. Interfaces 2018, 10 (38), 32413-32419.

2. Lee, T.; Sanzogni, A. V.; Burn, P. L.; Mark, A. E., Evolution and Morphology of Thin Films Formed by Solvent Evaporation: An Organic Semiconductor Case Study. ACS Appl. Mater. Interfaces 2020, 12 (36), 40548-40557.

 


Presentation
1:25 – 1:50pm

Balanced Hole and Electron Transport in TCTA:Ir(ppy)3 Blends as Determined by Photo-MIS-CELIV

Mile Gao1, Paul L. Burn,1* Almantas Pivrikas2

1Centre for Organic Photonics & Electronics (COPE), School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia
2Physics department, Murdoch University, Perth, Western Australia, 6150, Australia
* p.burn2@uq.edu.au

Balanced charge injection and transport in organic light emitting diodes (OLEDs) is essential for highly efficient devices with small efficiency roll-off at high luminance. However, there are few reports on the measurement of charge mobility within the blend emissive layer of an OLED. In this presentation, we show that photoexcitation in conjunction with Metal-Insulator-Semiconductor Charge Extraction with Linearly Increasing Voltage (photo-MIS-CELIV) can be used to determine the hole and electron mobilities of the emissive blend layer in a single device architecture. We demonstrate the technique by studying the commonly used emissive blend of fac-tris[2-phenylpyridinato-C2,N]iridium(III) [Ir(ppy)3] and tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as well as neat TCTA and Ir(ppy)3 films. It was found that Ir(ppy)3 and its blend films with TCTA have measurable electron mobilities and critically they are of similar magnitude as their hole mobilities, irrespective of the Ir(ppy)3 doping ratio. Such balanced charge mobility suggests that the transport of both holes and electrons occurs mostly on the Ir(ppy)3 guest molecules in the blend. Additionally, we demonstrate that photo-MIS-CELIV can be used to measure the quantum efficiency of exciton dissociation in organic semiconductor thin films.

1:50 – 2:00pm – Questions and discussion

During the seminar:

• Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.

• You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.

• If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars:

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts:

Seminars are typically held on the first Wednesday of each month.

At this time we are specifically encouraging HDR students to present their work to broad audience. If you are interested in speaking then please submit an abstract to bronson.philippa@jcu.edu.au.


Online Seminar Announcement: Wednesday 4 August 2021

Wednesday 4 August 2021

Time: 1pm in QLD, NSW, ACT, Vic, and Tas

11am in WA 12:30pm in NT

12:30pm in SA

3pm in New Zealand

Meeting URL: https://jcu.zoom.us/j/82093241646

Seminar schedule

Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed)

Presentation
1:00 – 1:25pm

Anisotropic Triplet Exciton Diffusion in Crystalline TIPS-Pentacene

Rohan J. Hudson, D.M. Huang and T.W. Kee

The University of Adelaide, Adelaide, South Australia, Australia

Singlet fission (SF) is a spin-allowed exciton multiplication process in which coupling of an excited singlet-state (S1) chromophore to an adjacent ground-state chromophore yields two triplet-state (T1) excited chromophores. This process has the potential to circumvent the theoretical efficiency limit for single-function photovoltaics, and as such has attracted significant interest in recent years. Organic SF chromophores typically exhibit significant structural anisotropy in their crystal packing, which can impact exciton transport and influence the design of SF-enhanced devices. An improved understanding of the link between structural anisotropy and exciton diffusion is therefore crucial for developing SF-based photovoltaics.
Here we use ultrafast transient absorption spectroscopy to quantify the anisotropy in the triplet exciton mobility of crystalline 6,13-(triisopropylsilylethynyl)-pentacene (TIPS-Pn), a prototypical SF chromophore. Bimolecular triplet−triplet annihilation in crystalline TIPS-Pn is well-described by a kinetic model that assumes isotropic, three-dimensional triplet exciton diffusion, but with physically unreasonable best fit parameters. Kinetic models that assume either one-dimensional or anisotropic three-dimensional exciton diffusion describe the data equally well but yield more physically realistic fit parameters, suggesting that triplet diffusion on the sub-nanosecond time scale occurs mostly along a single axis of the material. Diffusion coefficients calculated by density functional theory predict that triplet exciton diffusion occurs predominantly along the crystallographic a-axis, with migration in any other direction slower by over an order of magnitude. These findings highlight the need to treat parameters obtained from fits of experimental data with models of isotropic diffusion with caution for systems with anisotropic packing such as TIPS-Pn, and suggest that fast, directional exciton transport in layers or films of TIPS-Pn may be achieved by control of the chromophore morphology.

 

1:25 – 1:50pm

Structure-Property Relationships in Molecular Electronics

Masnun Naher,a Elena Gorenskaia,a Wenjing Hong,b Colin J. Lambert,c Richard J. Nichols,d Paul J. Low a*

a University of Western Australia, Australia;

b Xiamen University, China;

c Lancaster University, UK;

d University of Liverpool, UK

Molecular electronics (ME) is a rapidly maturing field concerned with the study of charge transport phenomena through a single molecule or an array of molecules organized between two (or more) macroscopic electrodes (Figure 1). By the careful design of the chemical structure it’s possible to study the different charge transport mechanism such as coherent tunneling and incoherent hopping and quantum interference phenomenon within the junction to achieve the functions of conventional electronic components such as chemical sensors and chemically-gated transistors (Chem-FETs), photodetectors, and thermoelectric materials.1
This presentation will describe the design and synthesis of range of linearly and cross-conjugated organic, organometallic and coordination complexes complex to study their electronic properties in the molecular junction. At the heart of this study is the exploration of the factors that influence electron transport through a molecule. In turn, this deeper understanding allows us to extend molecular design strategies beyond the search for highly conductive molecules and direct attention to more subtle concepts such as quantum interference,2 redox-gated molecular electronic response1 and the influence of the molecule-electrode contact1 and coupling to the overall electrical response of the junction (Figure 1). Molecular parameters such as the frontier orbital energy levels and HOMO-LUMO gap of the molecular candidates in their accessible redox states are therefore essential to these investigations. Therefore, in addition to the molecular junction-based measurements of molecular conductivity, investigation of the electronic structures and electrochemical properties of these molecular candidates using electrochemical, spectroelectrochemical and computational methods has also been undertaken.3

 

Figure 1: A schematic of a single-molecule junction, showing the conceptual features of the anchor group contacting to the electrode surface, a linking group or molecular backbone and some functional unit (e.g. a metal-ligand fragment).

The performance of the synthesised compounds to understand different charge transport mechanisms is being evaluated within scanning tunneling microscope break-junction (STM-BJ) in collaboration with Liverpool University (UK), and the theoretical calculations of molecular structure and model junctions were done in collaboration with Lancaster University (UK) and Xiamen University (China), and results will be reported.

References
1. M. Naher, D. C. Milan, O. A. Al-Owaedi, I. J. Planje, S. Bock, J. Hurtado-Gallego, P. Bastante, Z. M. Abd Dawood, L. Rincón-García, G. Rubio-Bollinger, S. J. Higgins, N. Agraït, C. J. Lambert, R. J. Nichols and P. J. Low, J. Am. Chem. Soc., 2021, DOI: 10.1021/jacs.0c11605.
2. F. Jiang, D. I. Trupp, N. Algethami, H. Zheng, W. He, A. Alqorashi, C. Zhu, C. Tang, R. Li, J. Liu, H. Sadeghi, J. Shi, R. Davidson, M. Korb, A. N. Sobolev, M. Naher, S. Sangtarash, P. J. Low, W. Hong and C. J. Lambert, Angew. Chem. Int. Ed., 2019, 58, 18987-18993.
3. M. Naher, S. Bock, Z. M. Langtry, K. M. O’Malley, A. N. Sobolev, B. W. Skelton, M. Korb and P. J. Low, Organometallics, 2020, 39, 4667-4687.

1:50 – 2:00pm – Questions and discussion

During the seminar:

• Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.

• You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.

• If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars:

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts:

Seminars are typically held on the first Wednesday of each month.

At this time we are specifically encouraging HDR students to present their work to broad audience. If you are interested in speaking then please submit an abstract to bronson.philippa@jcu.edu.au.


Online Seminar Announcement: Wednesday 7 July 2021

Due to the cancellation of many scientific conferences, the AUCAOS committee is pleased to announce an online seminar series. We intend to run seminars on the first Wednesday of every month until normal conferences can resume.

Date: Wednesday 7 July 2021

Time:
1pm in QLD, NSW, ACT, Vic, and Tas
11am in WA
12:30pm in NT
12:30pm in SA
3pm in New Zealand

Please note different times in some states due to the end of daylight savings time.

Click this link to join the meeting: https://jcu.zoom.us/j/84054173062

Seminar schedule
Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed): Presentation:
1:00 – 1:25pm Structural origins of long-range exciton diffusion in a non-fullerene acceptor

Dr Paul Hume
Victoria University of Wellington

In organic photovoltaic cells, absorption of light leads to the formation of excitons, which then diffuse to the donor/acceptor interface to generate photocurrent. The distance from which excitons can reach the interface is constrained by the exciton diffusion length, which has been difficult to quantitatively model or predict due to structural and energetic disorder. Modern non-fullerene acceptors have been shown to possess exceptionally large diffusion lengths, along with well-defined molecular and packing structures, suggesting that a predictive framework for materials design and computational screening may be possible.

We recently demonstrated1 that the large diffusion coefficient observed experimentally2 in an archetypical non-fullerene acceptor, IDIC, can be accurately quantified using density functional theory, and that the low energetic disorder means that the crystal structure provides a meaningful starting point to understand exciton motion in thin films. By accounting for short- and long-range excitonic interactions3, as well as spatiotemporal disorder, we can accurately predict experimental values for exciton diffusivity and diffusion length. The simplicity and accuracy of this approach are directly linked to the structural order of these materials, and an electronic coupling profile that is unusually resilient to thermal distortions – highlighting the potential for computational materials screening. Moreover, we show that these factors, combined with the low reorganisation energy and significant long-range electronic coupling, lead to diffusion rates that approach the upper limit of incoherent energy transfer, and long diffusion lengths that relieve constraints on organic solar cell device architectures.

1. P. A. Hume, W. Jiao, and J. M. Hodgkiss, J. Mater. Chem. C 2021, 9, 1419.
2. S. Chandrabose, K. Chen, A. J. Barker, J. J. Sutton, S. K. K. Prasad, J. Zhu, J. Zhou, K. C. Gordon, Z. Xie, X. Zhan and J. M. Hodgkiss, J. Am. Chem. Soc., 2019, 141, 6922.
3. P. A. Hume and J. M. Hodgkiss, J. Phys. Chem. A, 2020, 124, 591

1:25 – 1:50pm Characterising Exciton Generation in Bulk-heterojunction Organic Solar Cells

Kiran Sreedhar Ram1

1College of Engineering, IT and Environment, Purple 12, Charles Darwin University, Darwin, NT 0909, Australia
2Energy and Resources Institute, Charles Darwin University, 0909 Darwin, NT, Australia

The research and development in the field of organic solar cells (OSCs) have been thriving over the last few decades due to being of low cost, light weight and flexibility compared to the inorganic solar cells (ISCs). However, there are two major challenges in bringing OSCs to the commercial stage: i) low power conversion efficiency (PCE) and ii) low stability or degradation [1]. Bulk-heterojunction (BHJ) OSCs with an active layer based on fullerene acceptor have currently dominated the research activities in organic photovoltaic because of their excellent charge transport properties. However, fullerene acceptor materials have some disadvantages which include limited chemical and energetic tunability, narrow range of absorption spectra and unstable morphology thereby limiting the overall PCE and stability of the devices thus fabricated. Therefore, the research focus has moved to the use of non-fullerene (NF) acceptors in BHJ OSCs. In this research, work has been done in understanding the characteristics of exciton generation in conventional and inverted NF acceptor based BHJ OSCs and the results are also compared to fullerene acceptor based BHJ OSCs. [2]
The characterisation of exciton generation is carried out in three BHJ OSCs, OSC1: an inverted NF BHJ OSC, OSC2: a conventional NF BHJ OSC and OSC3: a conventional fullerene BHJ-OSC. It is found that the overlap of the regions of strong constructive interference of incident and reflected electric fields of electromagnetic waves and those of high photon absorption within the active layer depends on the active layer thickness. An optimal thickness of the active layer can thus be obtained at which this overlap is maximum. We have simulated the rates of total exciton generation and position dependent exciton generation within the active layer as a function of the thicknesses of all the layers in all three OSCs and optimised their structures. Based on our simulated results, the inverted NF BHJ OSC1 is found to have better short circuit current density which may lead to better photovoltaic performance than the other two. [2]

[1] K. S. Ram and J. Singh, “Highly Efficient and Stable Solar Cells with Hybrid of Nanostructures and Bulk Heterojunction Organic Semiconductors,” Advanced Theory and Simulations, vol. 2, no. 6, p. 1900030, 2019/06/01 2019, doi: 10.1002/adts.201900030.
[2] Sreedhar Ram K, Mehdizadeh-Rad H, Ompong D, Setsoafia DDY, Singh J. Characterising Exciton Generation in Bulk-Heterojunction

1:50 – 2:00pm Open discussion

 

During the seminar:

  • Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.
  • You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.
  • If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts

Seminars are held on the first Wednesday of each month.

In the spirit of building a community in these challenging times, you are encouraged to give a talk. Do you have a talk that you would have given at a conference that was cancelled? Please consider adapting that talk for this format.

Submit abstract by email to bronson[dot]philippa[at]jcu[dot]edu[dot]au.


Online Seminar Announcement: Wednesday 5 May 2021

Due to the cancellation of many scientific conferences, the AUCAOS committee is pleased to announce an online seminar series. We intend to run seminars on the first Wednesday of every month until normal conferences can resume.

Date: Wednesday 5 May 2021

Time:
1pm in QLD, NSW, ACT, Vic, and Tas
11am in WA
12:30pm in NT
12:30pm in SA
3pm in New Zealand

Please note different times in some states due to the end of daylight savings time.

Click this link to join the meeting: https://jcu.zoom.us/j/84611488938

Seminar schedule
Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed): Presentation:
1:00 – 1:25pm The Effects of Deposition Technique on Charge and Exciton Dynamics in OLEDs – A Computational Study

Stephen Sanderson
James Cook University & The University of Queensland

Solution-processed OLED films present a number of advantages in cost and scalability over their vacuum-deposited counterparts. However, they currently do not meet the same performance standards, tending to degrade at a faster rate. Towards understanding this, kinetic Monte-Carlo transport modelling combined with molecular dynamics deposition modelling offers a detailed picture of device operation, and allows for the establishment of structure-property relationships that can be difficult to observe through other means. This presentation gives an overview of KMC modelling techniques in the context of phosphorescent OLEDs, along with an outline of techniques developed for building thicker solution-deposited films without the need for prohibitively large initial systems. Using these techniques, a comparison is made between charge and exciton dynamics in solution- and vacuum-deposited OLED films with the goal of gaining insight into the cause of experimentally observed differences in degradation rate.

1:25 – 1:50pm Ternary Strategy and Burn-in Degradation Investigation of Organic Solar Cells

Leiping Duan
The University of New South Wales

Organic solar cells (OSCs) as a low-cost new generation of renewable energy technology have become a promising contender that could serve as an alternative to silicon to established photovoltaic (PV) technologies in the future. Meticulous active layer engineering is a crucial element for OSCs to improve the device performance, where the application of the ternary strategy is an effective pathway. The ternary strategy retains the simplicity of the fabrication for organic solar cells and exhibits a higher potential towards large-scale fabrication. Investigating the novel application of ternary strategy in OSCs is a promising method towards higher device performance. Apart from the pursuit of the device performance, research for the long-term OSCs device stability is also critical for its practical applications and future commercialization. Burn-in degradation has become an ineluctable barrier for OSCs to achieve long-time stability, where an in-depth understanding of the mechanism behind burn-in degradation has become the precondition to conquer this barrier.
The aim of research works in my PhD thesis is to improve the performance of OSCs and provide understandings of its degradation mechanism behind. The ternary strategy, especially incorporated with novel non-fullerene acceptor materials, as a performance improving method, is the primary focal point in this thesis. In this thesis, we derived three novel ternary OSCs and provided a comprehensive investigation of the mechanism behind its performance enhancement. On the other hand, this thesis also systematically investigated the burn-in degradation mechanism in OSCs. We analysed the degradation mechanism based on each instability factor including light, heat, and air, to gain in-depth understating. Moreover, combined with the application of ternary strategy and the burn-in degradation study, we did a case study of the burn-in degradation in the high-efficiency PTB7-Th: COi8DFIC: PC71BM ternary OSCs. We found that the ternary strategy could increase the stability of the device, and the burn-in degradation mechanism in ternary OSCs is more dependent on its dominant binary counterpart. Overall, insights gained in this work into the nature of ternary strategy and burn-in degradation provide a step for OSCs towards large scale application and future commercialization.

1:50 – 2:00pm Open discussion

 

During the seminar:

  • Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.
  • You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.
  • If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts

Seminars are held on the first Wednesday of each month.

In the spirit of building a community in these challenging times, you are encouraged to give a talk. Do you have a talk that you would have given at a conference that was cancelled? Please consider adapting that talk for this format.

Submit abstract by email to bronson[dot]philippa[at]jcu[dot]edu[dot]au.


Online Seminar Announcement: Wednesday 7 April 2021

Due to the cancellation of many scientific conferences, the AUCAOS committee is pleased to announce an online seminar series. We intend to run seminars on the first Wednesday of every month until normal conferences can resume.

Date: Wednesday 7 April 2021

Time:
1pm in QLD, NSW, ACT, Vic, and Tas
11am in WA
12:30pm in NT
12:30pm in SA
3pm in New Zealand

Please note different times in some states due to the end of daylight savings time.

Click this link to join the meeting: https://jcu.zoom.us/j/86449047647

Seminar schedule
Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed): Presentation:
1:00 – 1:25pm Organic Polariton Lasing with Molecularly Isolated Perylene Diimides

Dr. Girish Lakhwani
Sydney University

In the last decade, strong light matter coupling has become an alternative path to achieve lasing in organic materials via use of polaritons. Polariton lasers do not require population inversion and thus hold the promise of lower laser thresholds. Organic materials are particularly suited for polariton lasing as their large absorption coefficients result in impressive exciton-photon couplings strengths at room temperature. Here I will demonstrate polariton lasing in a molecularly isolated perylene diimide. [1,2] The emission exhibits threshold behaviour, spatial coherence, and the characteristic blue-shifting of polariton systems. We expect perylene dyes will become a useful polariton laser class.

1. Sabatini et al. J Mater Chem C, 7, 2954 (2019)
2. Sabatini et al. Appl. Phys. Lett, 117, 041103 (2020)

1:25 – 1:50pm Optimal quantum dot size for photovoltaics with fusion

Dr. Laszlo Frazer
Monash University

Light fusion increases the efficiency of solar cells by converting photons with lower energy than the bandgap into higher energy photons. The solar cell converts the produced photons to current. We use Monte Carlo simulation to predict that lead sulfide quantum dot sensitizers will enable fusion with a figure of merit on the mA/cm^2 scale, exceeding current records, while enabling silicon cell compatibility. Performance is highly sensitive to quantum dot size, on the order of mA/cm^2/nm.

1:50 – 2:00pm Open discussion

 

During the seminar:

  • Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.
  • You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.
  • If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts

Seminars are held on the first Wednesday of each month.

In the spirit of building a community in these challenging times, you are encouraged to give a talk. Do you have a talk that you would have given at a conference that was cancelled? Please consider adapting that talk for this format.

Submit abstract by email to bronson[dot]philippa[at]jcu[dot]edu[dot]au.


Online Seminar Announcement: Wednesday 10 March 2021

Due to the cancellation of many scientific conferences, the AUCAOS committee is pleased to announce an online seminar series. We intend to run seminars on the first Wednesday of every month until normal conferences can resume.

Date: Wednesday 10 March 2021

Time:
1pm in QLD
2pm in NSW, ACT, Vic and Tas
11am in WA
12:30pm in NT
1:30pm in SA
4pm in New Zealand

Click this link to join the meeting: https://jcu.zoom.us/j/81590417076

Seminar schedule
Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed): Presentation:
1:00 – 1:25pm N-Heterocyclic Carbene Platinum(II) Dialkynyl Complexes – A New Class of Highly Tunable and Efficient Emitter Systems

Assoc. Prof. Koushik Venkatesan
Macquarie University

New and efficient light-emitting materials are required for a broad range of potential applications in the fields of sensors, storage, photoelectronic devices, and optical devices. Extensive investigations on transition metal complexes as triplet emitters for application in phosphorescent organic light emitting devices (PhOLEDs) have been carried out. Metal complexes with specific ligand environment allow to tailor the luminescent properties in a precise fashion for a specific application. Achieving high stability, high quantum efficiency and specific chromaticity remains a major challenge in this field. Recently, our group has demonstrated a series of highly emissive platinum(II) complexes bearing N-heterocyclic carbene ligands with promising photophysical properties. Further building on this work, we have developed new series of small molecules and investigated their detailed luminescent properties. Selected molecules that have been fabricated into devices show high potential for applications in light emitting devices.

1:25 – 1:50pm Classification of Coherent Enhancements of Light-Harvesting Processes

Assoc. Prof. Ivan Kassal
The University of Sydney

Several kinds of coherence have recently been shown to affect the performance of light-harvesting systems, in some cases significantly improving their efficiency. Recently, we classified the possible mechanisms of coherent efficiency enhancements [1], based on the types of coherence that can characterize a light-harvesting system and the types of processes these coherences can affect. We show that enhancements are possible only when coherences and dissipative effects are best described in different bases of states. In addition, our classification allows us to predict a previously unreported coherent enhancement mechanism.

I will discuss the implications of this classification for the field of organic photovoltaics. Several coherent mechanisms have been proposed for boosting OPV efficiency, but most of them are impossible. A few manifestations of coherence may matter, including one that we are confident plays a big role in OPV performance [2].

[1] Stefano Tomasi and Ivan Kassal, J. Phys. Chem. Lett. 2020, 11, 2348–2355.

[2] Daniel Balzer, Thijs J.A.M. Smolders, David Blyth, Samantha N. Hood, and Ivan Kassal, Chem. Sci. doi:10.1039/D0SC04116E (2021).

1:50 – 2:00pm Open discussion

 

During the seminar:

  • Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.
  • You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.
  • If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts

Seminars are held on the first Wednesday of each month.

In the spirit of building a community in these challenging times, you are encouraged to give a talk. Do you have a talk that you would have given at a conference that was cancelled? Please consider adapting that talk for this format.

Submit abstract by email to bronson[dot]philippa[at]jcu[dot]edu[dot]au.


Online Seminar Announcement: Wednesday 3 February 2021

Due to the cancellation of many scientific conferences, the AUCAOS committee is pleased to announce an online seminar series. We intend to run seminars on the first Wednesday of every month until normal conferences can resume.

Date: Wednesday 3 February 2021

Time:
1pm in QLD
2pm in NSW, ACT, Vic and Tas
11am in WA
12:30pm in NT
1:30pm in SA
4pm in New Zealand

Click this link to join the meeting: https://jcu.zoom.us/j/89897826579

Seminar schedule
Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed): Presentation:
1:00 – 1:25pm A flexible organic solar cell based on doped graphene/PET substrate

Dr. Hellen Jin
The University of Queensland

Graphene has shown tremendous potential as a transparent conductive electrode (TCE) for flexible organic solar cells (OSCs). However, the trade-off between electrical conductance and transparency as well as surface roughness of the graphene TCE with increasing layer number limits power conversion efficiency (PCE) enhancement and its use for large-area OSCs. Here, we use a 300 nm-thick poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester as the photoactive layer and a benzimidazole (BI)-doped graphene as the transparent anode to demonstrate efficient OSCs with good flexibility. It is found that 3 layer (L) graphene had the best balance between sheet resistance, optical transmittance and surface roughness for optimized cell design. A 0.2 cm2 cell with a 3L BI-doped graphene anode achieves a PCE of 6.85%, which is one of the highest PCE values reported so far for flexible graphene anode-based OSCs. The flexible cells are robust, showing only a small performance degradation during up to 250 flexing cycles. Moreover, the combination of the thick photoactive layer with the optimized 3L BI-doped graphene TCE enabled production of 1.6 cm2 flexible OSCs with a PCE of 1.8%. Our work illustrates the importance of graphene TCE development for flexible OSCs as well as other wearable optoelectronic devices.

1:25 – 1:50pm Carbene-metal-amides as emitting materials in high-efficiency organic light-emitting diodes

Dr. Patrick Conaghan
University of Sydney / University of Cambridge

Emitting materials in organic light-emitting diodes are predominantly phosphorescent iridium complexes or all-organic thermally activated delayed fluorescence materials. We have demonstrated that the carbene-metal-amide molecular structure of coinage-metal complexes can also be used to produce organic light-emitting diodes with efficient electroluminescence from both singlet and triplet excited states.
We have shown that the emission colour can be changed through variation of the electron-donating strength of the donor moiety and the polarity of the host environment and have used both of these effects to produce devices with emission across the visible range. By engineering excited state energies we have fabricated green-emitting devices with a maximum electroluminescence quantum efficiency of 26.9 % and blue-emitting devices (Commission Internationale de l’Éclairage co‐ordinates [0.17, 0.17]) with external quantum efficiency of 20.9 %.
Transient photoluminescence measurements at varying temperatures show that the emission process is thermally activated with short excited-state lifetimes (<1 μs) and along with device data show that the energy of local triplet excited states imposes an energy limit on efficient emission. Carbene-metal-amides do not show a strong concentration-dependent luminescence quenching in the solid state, which has allowed us to fabricate host-free devices with external quantum efficiency of up to 23 % which, to our knowledge, is the highest reported for host-free organic light-emitting diodes.

1:50 – 2:00pm Open discussion

 

During the seminar:

  • Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.
  • You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.
  • If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts

Seminars are held on the first Wednesday of each month.

In the spirit of building a community in these challenging times, you are encouraged to give a talk. Do you have a talk that you would have given at a conference that was cancelled? Please consider adapting that talk for this format.

Submit abstract by email to bronson[dot]philippa[at]jcu[dot]edu[dot]au.