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Materials Engineering of Integrated Hybrid Spectral Converters for Next Generation Luminescent Solar Devices

Periodic Reporting for period 2 - SPECTRACON (Materials Engineering of Integrated Hybrid Spectral Converters for Next Generation Luminescent Solar Devices)

Reporting period: 2020-11-01 to 2022-04-30

Solar energy conversion will play a key role in our transition to a carbon-neutral society. However, single junction photovoltaic (PV) cells fail to achieve their theoretical efficiency due to an inability to harness all wavelengths of the solar spectrum. These spectral losses may be overcome through the addition of a spectral converter coating to the surface of a finished PV cell, which, through a photoluminescence process, converts sunlight into wavelengths that the PV cell can in principle use more effectively. Nonetheless, spectral converters currently fail to deliver their promise to significantly boost PV cell performance due to the difficulties of translating luminescent molecules – or lumophores – from solution into efficient solid-state materials.

In SPECTRACON, we are attempting to solve this problem by taking a “bottom-up” approach to the design of new spectral conversion materials in which the lumophore-host system is considered as an integrated unit by design, rather than as discrete components. The key objectives are to design, synthesise and understand the structural, mechanical and optical interactions between new hybrid polymer host materials in which lumophores are strategically placed (e.g. through chemical grafting or phase separation) and to test the ability of these systems to downshift or upconvert solar photons. The end goal is to develop a solution-based process suitable for scalable manufacturing, such that these spectral converters can be integrated with PV cells to realise next generation luminescent solar devices which display record levels of efficiency and reduced costs, helping to contribute to net zero targets.
The reporting period covers the first 30 months of the project. The team consists of three postdoctoral researchers and two postgraduate students. Despite the significant impact from the Covid-19 pandemic, to date we have made important advances in the design of new host systems, the integration of downshifting and upconverting lumophores and assessment of the photophysical performance.

The initial phase of the project (6 months) saw the recruitment of team members and the procurement and installation of key equipment required to perform the research (time-correlated single photon counting photoluminescence spectrometer and benchtop nuclear magnetic resonance spectrometer). During the first national lockdown, the team undertook a detail literature survey into host material requirements for downshifting and upconversion (Advanced Photonics Research, 2021, 2, 2000196, Macromolecules, 2021, 54, 5287-5878). This valuable work enabled us to identify new target host materials at the forefront of the state-of-the-art. Since the laboratory has re-opened (at reduced (30%) capacity until September 2021), we have focussed on the design and characterisation on new host systems based on organic-inorganic hybrids (Proc. SPIE 2020, 113670Y), copolymers and hydrogels. We have also advanced the design of luminescent solar concentrators (LSCs) based on aggregation induced emitters and energy transfer, in which selective phase separation boosts the photoluminescence efficiency (ACS Applied Polymer Materials, 2019, 1, 11, 3039-304, Journal of Materials Chemistry C, 2021, 9, 13914-13925.) In addition, with collaborators we have reported the design of LSCs that can be repaired with a single heat treatment upon damage (ACS Applied Energy Materials, 2020, 3, 1152-1160.). Exciting progress has also been made in the design of solid-state upconverting materials, in which performances and stability surpassing the state-of-the-art have been attained. We are currently preparing a manuscript to report these exciting results.

In addition, the team participated in the Cambridge Science Festival, preparing an outreach video to explain our work on solar spectral converters.
In the remainder of the project, the team aims to explore new compositions of host-lumophore materials with the goal of identifying the key design rules that will enable efficient conversion of sunlight in the solid-state. Armed with this knowledge, we aim to design new and improved spectral conversion coatings able to downshift, concentrate or upconvert sunlight so that it can be used more effectively by solar cells. This will involve the development of new, benign processing methods to enable the integration of these coatings with finished PV cells. Particular attention is being paid not only to the principles of Green Chemistry in our design process, but also solutions for end-of-life recycling and re-use. The knowledge developed through this project will also be directly translatable to cognate technologies such as energy efficient light-emitting displays, optical storage and communication.