Nitrogen-doped carbon nanodots/PMMA nanocomposites for solar cells applications

Carbon Nanodots (CNDs) are a novel class of nanocarbons that consist of discrete, quasi-spherical nanoparticles with sizes below 10 nm. Besides, due to their low cost, environmentally friendly and low toxicity, CNDs could substitute traditional semiconductor quantum dots (QDs), generally top luminescent materials, but usually made of heavy metals. A very interesting property of CNDs is their tunable emission, characterized by multi-fluorescence colors under varied excitation wavelengths. Photoluminescent CNDs properties give them potential applications in areas such as biomedicine, bioimaging, catalysis, optoelectronics and solar concentrators. Luminescent solar concentrators (LSC) are usually thin plates or sheets made of transparent polymers, such as poly(methyl methacrylate) (PMMA), doped with photoluminescent species. Direct and diffuse incident sunlight is absorbed by these species and the emitted visible light is guided through the polymer to be collected by attached solar cells, increasing their efficiency. CNDs are promising candidates as luminescent doping species for PMMA in preparing hybrid materials, which could be an advantageous and innovative alternative for solar cells applications. In this work, highly fluorescent nitrogen-doped CNDs (NCNDs) were prepared following a simple and controllable synthetic approach under microwave irradiation (MW). Arginine and ethylenediamine were used as carbon and nitrogen precursors and water as reaction medium. The MW parameters were optimized (240°C, 26 bar, 200 W, 180 sec) to obtain the desired properties of the final material, in terms of optical performance. Nanocomposites of NCNDs/PMMA were prepared by solution blending, with 0.1 wt.% and 0.01 wt.% of NCNDs, followed by film casting. The down conversion fluorescence behavior of NCNDs and NCND/PMMA nanocomposites were characterized by Photoluminescence spectroscopy. A broad emission peak at 356 nm was observed for the NCNDs when excited at 300 nm and the fluorescence peaks shift from 356 to 474 nm as excitation varies from 300 to 420 nm. On the other hand, the fluorescence of the NCNDs in the PMMA matrix showed significant broad emission at around 450 nm when excited between 300 and 320 nm.