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Luminescent solar concentrators (LSCs) are large-scale sunlight collectors, consisting of fluorophores embedded in waveguides, which can concentrate part of the absorbed sunlight at the borders of the slab through wave-guided photoluminescence. Benefiting from their low-cost and semi-transparency, they exhibit great potential for building integrated photovoltaics. Among various types of fluorophores, carbon quantum dots (C-dots) have attracted great interest due to their relatively high quantum yield (QY), low-cost, non-toxic composition and simple synthetic methods. Unfortunately, most red-emitting C-dots with high QYs were synthesized using relatively toxic and expensive precursors. The C-dots exhibiting red-emission synthesized using sustainable precursors (e.g. citric acid) have QYs less than 20%. Here we synthesized the red-emitting C-dots produced by using citric acid and urea as precursors and N,N-diethylformamide as the solvent via a solvothermal reaction. The red C-dots have a broad absorption from 300–650 nm, with a QY as high as 40% in ethanol. In addition, the C-dots exhibited good biocompatibility, even for a C-dot concentration up to 1000 μg mL−1. The LSC (LSC area 100 cm2) based on red C-dots exhibited a solar-to-electricity power conversion efficiency (PCE) of 1.9% under natural sunlight illumination (35 mW cm−2). We combined red-emitting C-dots with green-emitting C-dots prepared via a vacuum heating approach. By using a tandem structure, composed of two slabs each incorporating a different C-dot type, the obtained PCE of the LSC based on the combination of red and green C-dots further increases up to 2.3% (under the same irradiance equal to 35 mW cm−2), which is comparable to the reported PCEs for the LSCs based on C-dots or other types of fluorophores. This work indicates that the red-emitting C-dots produced by low-cost and environmentally-friendly precursors exhibit great potential as building blocks for the environmentally compatible LSCs. [ABSTRACT FROM AUTHOR]

We report on the effects of incorporation of different concentrations of carboxyl group (COOH)-functionalized multi-wall carbon nanotubes (F-MWCNTs) into TiO2 active layers for dye-sensitized solar cells (DSSCs). Standard DSSCs with bare TiO2 exhibit a photo-conversion efficiency (PCE) of 6.05% and a short circuit current density (Jsc) of 13.3 mA cm−2. The presence of 2 wt% F-MWCNTs in the photoanodes increases the PCE up to 7.95% and Jsc up to 17.5 mA cm−2. The photoanodes were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The electrochemical behaviour of the solar cells was investigated by electrochemical impedance spectroscopy (EIS). We attribute the improved performances to the combined effect of increased dye loading and reduced charge recombination (as clarified by dye loading and EIS measurements), due to the conformal coverage of F-MWCNTs, which allows fast and efficient charge collection in operating solar cells. These results can help in improving the PCE in DSSCs in an elegant and straightforward way, minimizing the need of additional steps (e.g. pre- and post-treatment with TiCl4) for photoanode preparation. [ABSTRACT FROM AUTHOR]