Efficient luminescent solar concentrators based on solvent polarity induced multiple-colored carbon dots.

Luminescent solar concentrators (LSCs) are large scale sunlight collector and can be used for building-integrated photovoltaics (BIPV). Achieving high-performance LSCs requires fluorophores with broad absorption, high quantum yield and a large Stokes shift. Nevertheless, conventional high-efficiency LSCs typically rely on heavy metal-based quantum dots as fluorophores. Herein, we demonstrated highly efficient LSCs by deeply understanding the polarity of boron-doped carbon nanodots (B-C-dots) in different solvents or polymers, such as polymethyl methacrylate (PMMA) or polystyrene (PS). The hydrothermally synthesized B-C-dots and undoped C-dots exhibit solvent dependent optical properties. Specifically, the emission peak shows a redshift when the C-dots are dispersed in ethanol, hexane and toluene, and the absorption edge shows a redshift with the increase of solvent polarity. For instance, the B-C-dots in toluene exhibit an absorption range of 300-600 nm and an emission peak of 605 nm, while in ethanol the absorption range extends to 300-650 nm and the emission peak is located at 438 nm. Once B-C-dots were dispersed in polymer matrices, the emission peak also shows various due to the different refractive index of polymers. As a proof-of-concept, we fabricated the LSCs (10 × 10 × 0.5 cm) by selecting different types of polymers. We are able to achieve the LSCs with different colors and the optimized LSC based on B-C-dots/PS exhibits an optical efficiency of 5.48 % under natural sunlight illumination (69 mW/cm). Our results pave a simple way to tune the colors and performance of the LSCs to achieve low-cost, highly efficient BIPV applications.