Platform Leader: Tim Schmidt
Deputy Platform Leader: Wallace Wong
Researchers
Solar Industry Partner
International Collaborators
The solar spectrum arrives at the Earth’s surface as broadband, white light characterised by the sun’s temperature of 6,000 kelvin.
Naturally, it contains all the colours of the rainbow, as well as colours we can’t see, like ultraviolet and infrared. However, solar cells and other excitonic applications only use one colour of light efficiently, that which is near their absorption threshold. For perovskite solar cells, like those in Platform 1.2, this is in the near infrared.
The goal of this platform is to tame the solar spectrum, by controlling the energy and spatial dimension of light. By doing this we aim to exceed the 30% Shockley-Queisser efficiency limit for light-to-electricity energy conversion.
Photon Upconversion is the process of converting two low-energy photons into one of higher energy. Designing materials which can exploit this process would allow us to utilise energy from the low energy (infrared) part of the Sun’s spectrum (which is wasted using existing technology) and transform it into higher energy so it can be converted into electric current.
Luminescent solar concentration is a process whereby the flux (energy density) of light hitting a surface can be increased by concentrating the light absorbed over a large area into a much smaller area by means of waveguiding. A Luminescent Solar Concentrator (LSC) can improve the efficiency of upconversion and also allow solar energy collection to be integrated into building architecture.
This platform aims to design high efficiency, solid-state, thin-film upconversion materials for solar energy applications. Our aim is to develop a hybrid material which will demonstrate 45% internal quantum efficiency under 10-sun equivalent illumination. This platform also aims to deliver robust and efficient materials and devices for LSCs. Within the first three years the researchers in this platform have designed, synthesised and characterised a range of new highly luminescent materials and incorporated these materials into LSC devices. The team has created several large-scale LSC devices, with one of those having the highest reported efficiency for a large area (400 cm2) LSC.
| Name | Node |
|---|---|
| Timothy Schmidt | UNSW |
| Dane McCamey | UNSW |
| Wallace Wong | UoM |
| Ken Ghiggino | UoM |
| Paul Mulvaney | UoM |
| Salvy Russo | RMIT |
| Asaph Widmer-Cooper | USyd |
| Alison Funston | Monash |
| Name | Node |
|---|---|
| Gary Rosengarten | RMIT |
| Angèle Reinders | TU Eindhoven |
| Name | Node |
|---|---|
| Thilini Ishwara | UNSW |
| Shyamal Prasad | UNSW |
| Siobhan Bradley | UoM |
| Kyra Schwarz | UoM |
| Nicholas Kirkwood | UoM |
| Igor Lyskov | RMIT |
| Laszlo Frazer | Monash |
| Stefano Bernardi | USyd |
| Name | Node | Student type |
|---|---|---|
| Riley O’Shea | UoM | PhD |
| Na Wu | UoM | PhD |
| Rehana Pervin | UoM | PhD |
| Timothy Warner | RMIT | PhD |
| Michael Rinaudo | USyd | PhD |
| Jiho Han | UoM | MSc |
| Paulo Simon | UoM | MSc |
| Rosie Pelosi | UNSW | PhD |
| Elham Gholizadeh | UNSW | PhD |
For the LSC part of the platform, we are meeting all the initial aims and objectives. We now have in-depth of knowledge in organic dye design for LSCs as well as their incorporation into polymer matrices of LSC devices. We can assemble LSC/photovoltaic devices and examine all performance parameters. We have added knowledge on stabilising quantum dot (QD) dispersions in polymer matrices. There are two outstanding items in our LSC program. We want to test the long-term stability of organic dyes and QDs in polymer matrices under one-sun conditions. We also need to find an appropriate application for LSC devices and are exploring a commercial partnership. As indicated in the report last year, we planned to combine LSCs with other light-harvesting devices. A planned project on combining flexible LSCs with flexible solar cells has stalled because of COVID19 disruptions. The project will continue when we have appropriate personnel. There is also a project to combine upconversion and LSCs but that has also stalled because of lack of personnel.
We have identified the Australian company ClearVue as a potential partner for commercialising LSC IP. An NDA was signed in October 2020 and we are discussing collaboration pathways. LSCs also figure prominently in the Centre’s Outreach activities, including a Victorian Laneway Art initiative, or similar large-scale activation, in 2021.
For the upconversion part of the platform, we demonstrated upconversion from below the bandgap of silicon using lead sulfide (PbS) QDs as sensitisers and violanthrone as the emitter. We also had some initial promising data on the use of conjugated polymers as emitters but we have hit a road block with those materials. The disorder in polymers and the low triplet exciton lifetime is a very difficult problem to tackle. Our organic nanocrystal work showed some promise for solid state upconversion devices. While we have only worked in upconverting green to blue, we can see an opportunity to use crystal engineering approaches to achieve highly ordered solid state materials optimised for upconversion.
In 2019, we reported a large-area LSC (gain = 50) which showed power-conversion efficiency (PCE) = 2.6% with a perovskite solar cell under one-sun with flux gain (F) = 7.4. F=14 at G=50 for narrow band (515 nanometres) irradiation was achieved. In 2020, we have been working to increase the light harvesting range by incorporating more chromophores. We examined both organic dyes and QDs and successfully combined a UV/blue light absorbing QD with two organic dyes in an energy transfer system. We expect publication of this result in 2021.
The use of isolated organic fluorophores with emissive aggregates resulted in a very efficient Förster resonance energy transfer (FRET)-based light-harvesting system. The study showed the power of controlling intermolecular interactions bringing us a step closer to natural photosynthetic light harvesting systems. With partners in New Zealand, UNSW demonstrated enhanced emission in red and orange perylene diimide organic dye ligands through the transfer of energy harvested by CsPbBr3 nanocrystal.
RMIT student Tim Warner has been working on embedding QDs and fluorescent polymers in various Polymethyl methacrylate (PMMA) composites. In addition, he has started using polyvinyl butyral (PVB) as the matrix. This polymer is being used by the company ClearVue to make commercial LSC devices. Our goal is to disperse QDs and nanophosphors into PVB for testing by ClearVue.
Existing LSC simulation programs have been compared and new code developed for various LSC geometries (UNSW, UoM, RMIT). This work has been published. Work is underway to extend the code to simulate rod-shaped chromophores, with initial results suggesting that alignment of nanorods could help enhance device efficiency (USyd, UoM, RMIT).
Research on controlled assembly of QD structures by theory (USyd, UoM) and experiment (Monash, UoM), and assess usefulness for LSCs in progress.
The UNSW node has fabricated and characterised thin film upconvertors based on conjugated polymers. These demonstrate the importance of film plasticity for triplet mobility. A publication is in preparation.
The apparatus for measuring triplet exciton mobility is operational and ready for use in this platform and available for projects across the Centre. Triplet exciton mobility is an important parameter in the control of excitons and in solar and light emitting technologies.
Materials:
RMIT investigated the theory of triplet mobility in MEH-PPV and found it to be very fast. UNSW and Monash published a theoretical analysis and code for upconvertor simulation.
Molecular Photonics Laboratory at UNSW
COVID19 is significantly impacting research progress across the Centre.
In addition to periods of lockdown blocking laboratory access, many projects are stalled because of difficulty sourcing requisite personnel. The impact has been more severe in Melbourne, where there were severe restrictions for long periods. Very little laboratory experimental work was achieved during this period. At UNSW, the replacement for the principal postdoctoral researcher allocated to upconversion experiments departed for New Zealand due to personal reasons amid the pandemic. No on-site replacement was possible. Further, the femtosecond lab at UNSW was inoperable for six months with no service engineer able to visit to expedite repair due to travel restrictions. As such, laboratory work at both sites was severely interrupted in 2020.
At this stage, it is unknown how significant the impact will be going into 2021. We expect that we will continue to have issues recruiting students and postdocs from overseas going well into 2021. For the next year or two, we may need to recruit more local students and postdocs.
We are in initial discussions with ClearVue, an Australian company based in Perth, about commercialising a building-integrated photovoltaic product with luminescent solar concentrator technology. The Centre is looking into dyes that ClearVue can use in their clear glass products. One key aspect is the incorporation of dyes into polyvinyl butyral (PVB), a widely used polymer coating on windows and other building components.
Prof John Anthony (U Kentucky) provided acene materials.
Prof Yi Zeng and Prof Huanli Dong (Chinese Academy of Sciences, Beijing) enabled access to upconversion quantum yield measuring equipment for solid state samples.
Prof Karl Krämer (University of Bern) providing lanthanide upconversion materials for NIR hybrid upconversion project.
Perylene diimide derivatives from the group of CI Wong are proving to be very popular materials for this platform as well as for organic polariton lasers. This has placed pressure on the supply of these materials. There are some synthetic challenges in upscaling the production so more effort will be placed on this problem.
CIs Mulvaney, Schmidt and Wong are continuing to work on the problem of dispersing both organic dyes and QDs in polymer matrices. CI Wong has a PhD student working on assembling multi-dye polymer nanoparticles as easily dispersible light harvesting materials.
CI Schmidt is working with AI Reinders on coupling LSCs with bifacial silicon solar cells. CI Wong is supplying the organic fluorophore for this project.
CI Mulvaney, CI Widmer-Cooper and AI Rosengarten are working on dispersing and aligning nanorods for LSC applications, as well as expanding the Centre’s LSC simulation code to handle rod-shaped chromophores. We will look at setting up long-term stability testing for LSC devices.
Moving forward, CIs Schmidt and Wong have an interest in applying the Melbourne perylene derivatives to Agrivoltaics. Perylene diimides harvest principally the green part of the solar spectrum, which is unused by plants. Significant opportunities exist in synergic applications of LSCs in agriculture.
CI Schmidt has plans to make improvements on the PbS/violanthrone system through PbS surface ligand modification.
McCamey, Schmidt and Wong groups are very keen to examine the unprecedented magnetic field effects on the upconversion performance of oligomeric emitters. There is a Masters student working on the synthesis of the oligomers.
Ghiggino and Mulvaney have initiated a new project for near IR upconversion under intense light concentration conditions. This project will be based on a hybrid QD light harvesting/lanthanide upconverter system integrated with bifacial solar cells and involves collaboration with local and international collaborators. Dr Kyra Schwarz, a new postdoctoral appointee, is working on this project.
Recent developments in visible-to-ultraviolet upconversion enable solar photocatalysis, particularly for H2 production. We will investigate this in collaboration with local colleagues in this space.
CI Wong has a PhD student working on assembling multi-dye polymer nanoparticles as easily dispersible light- harvesting materials.