Transparent and colour-neutral luminescent solar concentrators using bright Eu3+ supramolecular cages towards photovoltaic windows

Abstract

The integration of photovoltaic (PV) devices into the built environment has become a key factor for the development of energy efficient buildings. Luminescent solar concentrators (LSCs) are well suited for this application, as they could be installed over architectural elements inaccessible to conventional PVs. In the present work, we report the synthesis of super-bright [Eu₂L₄]²⁻ cages bearing bis-β-diketonate ligands and their subsequent embedding in polymethylmethacrylate (PMMA) by casting of 5 × 5 × 0.27 cm³ planar LSCs. With a measured average visible transmittance (AVT) of 92%, the proposed LSCs possess excellent transparency and aesthetic quality fit for glass destined for neutral colour applications. Moreover, the obtained materials absorb from 60% to 90% of solar UV radiation, exposure to which is harmful for human health and responsible for fading of building interiors. The performance of devices attained by edge-coupling LSC slabs with monocrystalline silicon solar cells matches that of classic Eu³⁺-based concentrators. Nonetheless, the employment of super-bright [Eu₂L₄]²⁻ luminophores allows the reduction of the Eu³⁺ ion content of our devices down to 0.01% wt. This denotes a most efficient use of a valuable material like europium in the developed LSC-PVs, as Eu³⁺ weight contents reported in relevant literature were one to two orders of magnitude higher.