Limits of Visibly Transparent Luminescent Solar Concentrators

Abstract

surfaces into energy harvesting resources. This new approach to visibly transparent LSCs was developed by exploiting the nature of excitonic semiconductors to optimize the use of this light-exposed surface area without compromising its existing functionality, thereby avoiding the aesthetic tradeoffs that can hinder adoption. Recent work has demonstrated devices that selectively harvest different parts of the solar spectrum including i) ultraviolet (UV) absorption, with massive downconverted luminescence deeper into the NIR (>400 nm) [4] and ii) near-infrared (NIR) absorption, with even deeper luminescence in the NIR. [3] This work has been subsequently followed by a number of other groups. [8][9][10][11][12] In contrast to transparent photovoltaics, which have also been developed to exploit this untapped area, [13][14][15] this new concentrator approach offers an alternative pathway whereby energy is transported optically, offering a simple route to large-area manufacturing, high defect tolerance, angle independent performance, and low-level energy cost. In this progress report we discuss the theoretical limits of transparent LSCs, idealized configurations, scalability, and properties of enabling materials. Operating Principles of LSCsLuminescent solar concentrators operate based on the following mechanisms (see Figure 1a): a portion of solar spectrum is absorbed in a luminescent dye (or "luminophore") [16] embedded in a transparent waveguide. That absorbed solar energy is then re-emitted at another wavelength isotropically in all directions within the waveguide, provided the oscillators are not preferentially oriented. Due to the index of refraction difference between the waveguide and the ambient environment the re-emitted photons are predominately trapped by total internal reflection, causing them to be directed towards the waveguide edges where they can be converted to electrical power in an edge mounted photovoltaic cell. The overall system power conversion efficiency, η LSC , is then given by:where η Opt is the optical efficiency (number of photons reaching the waveguide edge)/(number of photons incident on the waveguide), R is the front face reflection, η Abs is the solar spectrum Visibly transparent solar harvesting surfaces are an exciting new approach to harvesting solar energy around buildings and mobile electronics to improve their efficiency and autonomy without impacting their appearance. The recent demonstration of ultraviolet (UV) and near-infrared (NIR) selective light harvesters have enabled transparent luminescent solar concentrators (LSCs) that boast unparalleled scalability, flexibility, aesthetic quality, and affordability. Consequently, the question of the efficiency limits has emerged in these new systems. In this perspective, the theoretical efficiency limits of these concentrator systems are reviewed and practical considerations are outlined to approach these limits. For UV and UV/NIR selective harvesting single-junction transparent LSCs are constrained thermodynamically to 21%, which i...

Luminescent Solar Concentrators Based on Aggregation Induced Emission

“…A low dye content is actually associated to a modest capability to harvest sunlight. LSCs based on NIR‐emissive dyes with visible‐light transparency have been also proposed, but light harvesting efficiency is barely reached . Nevertheless, maximum power efficiency for LSCs was recorded for PMMA slabs or films coated on glass and embedding perylene‐based fluorophores .…”

Spectrally-Selective Energy-Harvesting Solar Windows for Public Infrastructure Applications

“…In particular, in concentrators relying on the LSC principle, the selection of luminophore materials is usually based on the requirement to harvest the energy within both the UV and also the near-IR spectral regions. Luminescent materials with large Stokes shift values are required to avoid excessive loss of light due to self-absorption [1][2][3][4]7,20,21].…”

“…Theoretical performance limits for high-transparency window-type luminescent concentrators have been reported recently in Reference [20]. An alternative way of calculating the same performance limit for an arbitrary level of window transparency presumes the idealized (complete) optical power collection of all available incident light by solar cells of known efficiency.…”

“…Future BIPV technologies are widely expected to feature a combination of energy-saving functionality due to superior thermal insulation properties provided by advanced glazing systems and low-emissivity coatings and smart-window functionality offering active control over window transparency along with a possibility of significant energy-harvesting performance available in increasingly high-transparency glazings [8,9,20]. The motivation for producing this article has been to highlight the emergence of a new class of highly-transparent solar windows, which are now ready for industrialization and to compare the performance metrics of this emergent solar-window technology with other examples of solar window-type devices.…”

Hoch fluoreszierende Pyridiniumbetaine für die Lichtsammlung

“…Die optische Quanteneffizienz (OQE) eines jeden Gerätes verringerte sich langsam gegenüber dem geometrischen Zuwachs (G), sodass ein geringer Reabsorptionseffekt in 1 e ‐basierten LSCs zu erwarten ist. Die OQE des 5 m m LSC verbleibt bei einem Wert von etwa 63 % für G=75 und zeigt damit eine ähnliche Leistungsfähigkeit wie die besten transparenten LSC‐Apparaturen . Darüber hinaus erhöhte sich der Strömungszuwachs fast linear gegen einen geometrischen Zuwachs von bis zu G=75 (S32).…”