Nanomaterials for Reabsorption Reduction and Elimination in Luminescent Solar Concentrators

Solar energy has the potential to satisfying the heavy energy demands from modern and future society. Solar cells have seen excellent progress in terms of efficiency, but poor progress in terms of versatility and palatability for integration into modern infrastructure. Luminescent solar concentrators are devices that concentrate light via luminescence within a waveguide. They may be coupled to solar cells to improve versatility, with a particularly powerful potential for the normalisation of building integrated photovoltaics.

Problematically, the main barrier preventing the commercialisation of luminescent solar concentrators, is that they suffer from reabsorption, where emitted waveguided light is parasitically reabsorbed by a luminophore. The design and synthesis of luminophores with inherently low reabsorption is necessary to push luminescent solar concentrators into modern energy infrastructure. This thesis explores several classes of materials and their use in luminescent solar concentrators.

Firstly, by utilising a FRET-based discrete hybrid quantum dot-to-dye luminophore composed of InP/ZnS-rhodamine 101 in a luminescent solar concentrator, we were able to show a mean efficiency increase of 50% in the hybrid system relative to InP/ZnS alone under 405 nm illumination (10 × 10 × 0.3 cm).

Secondly, we reversed the above system and explored FRET-based discrete hybrid dye-to-quantum dot luminophores for luminescent solar concentrators, and uncovered evidence of energy transfer in such a system to be limited due to the long-lived excited state of the quantum dot blocking transfer from short-lived excited state dyes.

Thirdly, we then moved on to single component heterojunction systems, namely CdSe/CdS nanotetrapods. Light is dominantly harvested by CdS in this luminophore, and subsequently emitted from the CdSe core, leading to a large stokes shift. We were able to show the complete elimination of reabsorption in a CdSe/CdS nanotetrapod based luminescent solar concentrator device, and achieve an external photon efficiency of 4.9 ± 0.9% under AM1.5G illumination (10 × 10 × 0.3 cm).

Finally, expanding on this idea we synthesised Cd, Pb free InP/ZnSe/ZnS nanotetrapods and evaluated their photophysical properties to determine if they would be suitable for use in luminescent solar concentrators. We determined that the synthetic route taken to form InP/ZnSe/ZnS nanotetrapods led to diminished photophysical properties, making them unsuitable for luminescent solar concentrators.

In summary we screened several classes of nanomaterials for luminescent solar concentrators, and found great potential exists for quantum dot-to-dye and nanotetrapod luminophores in terms of reducing/eliminating reabsorption for luminescent solar concentrators (in turn, increasing their efficiencies).

This work is a significant contribution to the luminescent solar concentrator field as it introduces new classes of nanomaterials to be explored and optimised in depth.