Mark Portnoi1 Christian Sol1 Tom Robbins1 Johannes Schlaefer1 Clemens Tummeltshammer1 Ioannis Papakonstantinou1

1, Electronic and Electrical Engineering, University College London, London, , United Kingdom

Structural flexibility of photovoltaic devices can lead to an expanse of applications such as wearable technologies, flexible electronics, self-powered sensors and roll-to-roll manufactured smart facades.

Luminescent solar concentrators (LSCs) composed of flexible host matrices such as polydimethylsiloxane (PDMS) have been proposed as a means of providing this flexibility. The elastomer sheets doped with luminophores can be fabricated in a range of sizes, transparencies, colours and rigidities to the designer’s needs.

This additional functionality can come at a cost to efficiency. Curvature results in increases in both reabsorption and escape cone losses. In this work we explore how curvature affects these losses and propose a solution for their mitigation. We investigate the effect of curvature on LSC efficiency by means of an experimentally verified Monte-Carlo model (MCM) for curved LSCs. We show that for large scale devices, the optimal concentrations of fluorophore concentrations at fixed thicknesses required to achieve the highest external optical efficiency differ for curved and flat LSCs.

To mitigate escape cone losses, we propose flexible distributed Bragg reflectors (DBRs) consisting of alternating PDMS and PDMS-titanium composite thin films with a refractive index contrast of ~0.3. These DBRs are designed to have omnidirectional reflectivity in the spectral region of the emission of the luminophores but high transmission in the absorption region. We fabricate prototype DBRs and compare reflectance to transfer matrix model (TMM) calculations. Combining our MCM and TMM into a hybrid package we optimise the application of such DBRs to Lumogen Red 305 doped flexible LSCs and demonstrate the DBR effect on their efficiency. We then use the model to predict the full potential of this pairing.

This work will pave the way for efficient and deformable LSCs. We plan to incorporate these into devices for use in everyday life.