Online Seminar Announcement: Wednesday 4 November 2020

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 4 November

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:

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 Partial Delocalisation Enhances the Efficiency of Charge Separation in Organic Photovoltaics

Daniel Balzer
The University of Sydney

In organic photovoltaics, the question of how charges are able to overcome their significant coulombic attraction and separate has attracted heated debate. In particular, the low dielectric constants in organic semiconductors produce coulombic barriers that are an order of magnitude greater than the available thermal energy. One of the proposed answers is delocalisation, including arguments that the increased separation of charges in the CT state reduces the coulombic barrier. However, it turns out that delocalisation stabilises the CT state and increases the coulombic barrier, and therefore any benefit provided by delocalisation must come from non-equilibrium kinetic effects. However, charge separation is a two-body problem involving the correlated motion of an electron and a hole, meaning that the computational difficulty is roughly the square of the single-body mobility calculation, meaning that a fully quantum-mechanical treatment has so far proved intractable in three dimensions. A complete kinetic model would help settle the debate about the main drivers of charge separation, and unite the proposed mechanisms including delocalisation, entropy and energy gradients. Last year, we presented delocalised kinetic Monte Carlo (dKMC), the first three-dimensional model of partially delocalised charge and exciton transport in materials in the intermediate disorder regime. Here, we use dKMC to make the charge separation problem computationally accessible, allowing the first simulation of the full dynamics (and, therefore, efficiency) of charge separation in the presence of disorder, delocalisation, polaron formation and noise. We find that small amounts of delocalisation can produce large enhancements in the efficiency at which charges separate.

1:25 – 1:50pm Spatially Correlated Quantum Properties in Organic Light Emitting Diodes

William Pappas
The University of New South Wales

Electronic spin is a quantum mechanical property that is fundamental to the charge-light conversion processes in optoelectronic devices. The suppression of interactions between spins in organic semiconductors leads to relatively long relaxation times (μs) and results in the formation of weakly coulombically bound electron-hole pairs. The ability to access and modulate the spin polarisation of these pairs enhances the quantum efficiencies of device DC observables (current, luminosity), while also enabling unique functionality in spin-logic devices.
In organic light-emitting diodes, the study of spin-dependent processes giving rise to magnetic field effects have been treated monolithically. We have incorporated optical imaging microscopy into a traditional magneto-electroluminescence (MEL) setup that has allowed us to discern the intra-device variation of the quantum property (hyperfine interaction) which is responsible for these effects. We investigated the correlations between these local hyperfine field strengths in both the spatial and temporal domains. Magnetic resonance measurements are then used explain the origin of variations in the MEL lineshapes.
This work is an important step in characterising the homogeneity of spin-dependent properties in organic materials which critically control the ability to manipulate spins in organic spintronic devices.

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:

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.