Periodic Reporting for period 1 - SOLIDUPCONVERSION (Active Triplet-Mediator Matrices for Efficient Solid-State Triplet-Triplet Annihilation Photon Upconversion Devices)
Reporting period: 2022-12-01 to 2024-11-30
Solar irradiation offers the possibility of clean and renewable energy worldwide. One major challenge for solar energy conversion is the uncollected and wasted energy from the solar spectrum, photons with energy lower than the bandgap of photovoltaic materials are lost. A mere 1% utilization of low bandgap photons in today’s solar energy installations would result in an additional 3 GW produced capacity, equivalent to 5 nuclear power plants. Triplet-triplet annihilation upconversion (TTA-UC) provides the possibility to convert two photons of low energy to one of high energy even at low irradiation intensity. This allows the two unused photons otherwise penetrating the photovoltaic to be transformed into one useable photon The development of efficient TTA-UC systems, compatible to solar energy harvesting devices is therefore of pivotal importance. This project aims at fabricating a material that enables efficient solar energy harvesting at low photon energies. Specifically, we will do this through solid state triplet-triplet annihilation upconversion. I will employ novel organometallic sensitizers that allow for low energy harvesting. These sensitizers will be incorporated into an active host matrix that replaces molecular diffusion, with triplet exciton diffusion. This is a novel realisation of energy transfer in the solid state and will circumvent current limitations in solid state upconversion. This will yield an efficient TTA-UC solid state material that can be applied to devices. By fulfilling these tasks, this research project will ultimately contribute to a new strategy for enhancement of solar energy conversion.
The scientific work carried out led to completion of three main achievements. Firstly, the synthesis of three porphyrin based sensitisers was carried out, this was done using traditional wet lab synthesis and products were characterised according to good practices set out by leading academic journals. The porphyrins were further tested for their photophysical properties; meaning we could test a variety of energy capture ranges, along with energy transfer characteristics and then decide on which was the most efficient in our system overall. Secondly, we used steady state and time-resolved spectroscopy to understand the efficiencies of our trimeric blend for upconversion. We did this by taking the quantum yield of emission when the trimeric blend is present and when only two components are present. We found that a Hetero-annihilation mechanism in the trimeric blend led to higher efficiencies and a greater energy upconversion at low photon flux, but as the photon flux is raised the traditional Homo-TTA mechanism becomes dominant. This result is the first time this has been conclusively demonstrated experimentally. Finally, the last piece of the puzzle was to model the path of photons/electrons in the trimeric blend computationally. This was carried out in collaboration from an expert group working in the Netherlands. Monte-Carlo simulations of TTA systems are few and far between, and to the authors knowledge have never been done for solid state systems. The computational simulations were a success, matching with the experimentally observed results and are the first example of this technique being successfully implemented for trimeric TTA blends. We have little doubt there will be a great interest in the field to use the developed simulations.
The main impact and value of this work is to the research community. With the systems we have been tested experimentally, and the computational simulations that have been developed through this project, we believe that the research field will further develop our published work. Further research into Hetero-TTA systems and computational modelling of exciton transport in solid state systems will lead to a greater understanding of how to increase TTA efficiency in the solid state. In turn this will help to develop more efficient add on technologies for photovoltaics, and increase solar energy capture and use.