Utilizing molecular states of carbon quantum dots (CQDs) to efficiently harvest outdoor and indoor energy via luminescent solar concentrator

Luminescent solar concentrators (LSCs) offer a huge potential for electricity generation due to their ability to harvest direct and diffused light. Among numerous fluorophores for LSCs, carbon quantum dots (C-QDs) are promising candidates due to their non-toxic nature, tunable optical features, and cost-effective synthesis. State-of-the-art LSCs utilizing C-QDs focus on solar energy harvesting, while their potential to harness indoor light for electricity generation is yet to be explored. In this study, we rationally fabricated C-QDs based LSC for efficient energy harvesting under both outdoor and indoor illuminations. Through a facile solvothermal pyrolysis technique, we synthesized the molecular states assisted C-QDs exhibiting a strong absorbance in the visible region that matched well with the outdoor and indoor light spectra. Laminated LSCs were fabricated by coating C-QDs/polyvinyl alcohol (PVA) film (photoluminescence quantum yield 71 %) on two glass substrates and joining them with an interlayer of refractive index matching polymer. Given geometry not only protects C-QDs/PVA film from external damage but also prevents light scattering losses that were prominent in an open C-QDs/PVA layer. External efficiency (η_ext) of the small-to-large area LSCs under different illuminations were estimated using an analytical approach. The results showed that under outdoor (air mass 1.5 global spectrum) illumination and without scattering background, a large-area (10 × 10 × 0.6 cm³) LSC at an optimized concentration of C-QDs exhibited η_ext of 3.1 %. When connected with the silicon PV cell, the same LSC yielded a power conversion efficiency (η_PCE) of 0.34 %. Among various indoor illuminations (light-emitting diode (LED)-daylight, LED-warm white, and fluorescent-daylight (CFL)), the best performance was shown under LED-daylight with the η_ext and η_PCE of 7.4 % and 0.30 %, respectively. This study offers enormous potential for the adoption of C-QDs based LSC not only in building exteriors (such as windows and facades) but also in the places where artificial lights are used.