A review of carbon quantum dots and their applications in wastewater treatment.

Luminescent solar concentrators (LSCs) are large-area sunlight collectors coupled to small area solar cells, for efficient solar-to-electricity conversion. The three key points for the successful market penetration of LSCs are: (i) removal of light losses due to reabsorption during light collection; (ii) high light-to-electrical power conversion efficiency of the final device; (iii) long-term stability of the LSC structure related to the stability of both the matrix and the luminophores. Among various types of fluorophores, carbon quantum dots (C-dots) offer a wide absorption spectrum, high quantum yield, non-toxicity, environmental friendliness, low-cost, and eco-friendly synthetic methods. However, they are characterized by a relatively small Stokes shift, compared to inorganic quantum dots, which limits the highest external optical efficiency that can be obtained for a large-area single-layer LSC (>100 cm2) based on C-dots below 2%. Herein, we report highly efficient large-area LSCs (100–225 cm2) based on colloidal C-dots synthesized via a space-confined vacuum-heating approach. This one batch reaction could produce Gram-scale C-dots with a high quantum yield (QY) (∼65%) using eco-friendly citric acid and urea as precursors. Thanks to their very narrow size distribution, the C-dots produced via the space-confined vacuum-heating approach had a large Stokes shift of 0.53 eV, 50% larger than C-dots synthesized via a standard solvothermal reaction using the same precursors with a similar absorption range. The large-area LSC (15 × 15 × 0.5 cm3) prepared by using polyvinyl pyrrolidone (PVP) polymer as a matrix exhibited an external optical efficiency of 2.2% (under natural sun irradiation, 60 mW cm−2, uncharacterized spectrum). After coupling to silicon solar cells, the LSC exhibited a power conversion efficiency (PCE) of 1.13% under natural sunlight illumination (20 mW cm−2, uncharacterized spectrum). These unprecedented results were obtained by completely suppressing the reabsorption losses during light collection, as proved by optical spectroscopy. These findings demonstrate the possibility of obtaining eco-friendly, high-efficiency, large-area LSCs through scalable production techniques, paving the way to the lab-to-fab transition of this kind of devices.

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Gram-scale synthesis of carbon quantum dots with a large Stokes shift for the fabrication of eco-friendly and high-efficiency luminescent solar concentrators

The insufficient utilization of sunlight has been a big obstacle preventing inorganic perovskite solar cells (PSCs) from achieving high power conversion efficiency (PCE). Herein, nitrogen-doped graphene quantum dots (N-GQDs) are developed to achieve a photoluminescence quantum yield (PLQY) as high as 80% to effectively convert harmful UV light into useful visible photons for improved solar cell efficiency. It is found that the N-GQD material is very stable against humidity and under high temperature stress. When it is deposited on the top of the γ-CsPbI3 PSCs, it serves as an energy-down-shift (EDS) layer to harvest light in the short wavelength range <350 nm that is normally detrimental to the perovskite. Compared with the reference cell without the N-GQDs, the optimized PSC exhibits an increased short circuit current density (JSC) of 19.15 mA cm−2 from 18.67 mA cm−2 and a PCE of 16.02% from 15.53%. Further examination of the EQE, PL and UV-vis absorption spectra confirms that the improvement in the device performance does indeed result from the N-GQDs. The present strategy paves the way for rational design to improve the performance of other novel photovoltaic devices.

Nitrogen-doped graphene quantum dots for 80% photoluminescence quantum yield for inorganic γ-CsPbI3 perovskite solar cells with efficiency beyond 16%

An overview of various configurations of Luminescent Solar Concentrators for photovoltaic applications

Luminescent solar concentrators (LSCs) have attracted significant attention as promising solar energy conversion devices for building integrated photovoltaic (PV) systems due to their simple architecture and cost-effective fabrication. Conventional LSCs are generally comprised of an optical waveguide slab with embedded emissive species and coupled PV cells. Colloidal semiconductor quantum dots (QDs) have been demonstrated as efficient emissive species for high-performance LSCs because of their outstanding optical properties including tunable absorption and emission spectra covering the ultraviolet/visible to near-infrared region, high photoluminescence quantum yield, large absorption cross sections, and considerable photostability. However, current commonly used QDs for high-performance LSCs consist of highly toxic heavy metals (i.e., cadmium and lead), which are fatal to human health and the environment. In this regard, it is highly desired that heavy metal-free and environmentally friendly QD-based LSCs are comprehensively studied. Here, notable advances and developments of LSCs based on unary, binary, and ternary eco-friendly QDs are presented. The synthetic approaches, optical properties of these eco-friendly QDs, and consequent device performance of QD-based LSCs are discussed in detail. A brief outlook pointing out the existing challenges and prospective developments of eco-friendly QD-based LSCs is provided, offering guidelines for future device optimizations and commercialization.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201801967

Eco-Friendly Colloidal Quantum Dot-Based Luminescent Solar Concentrators.

Carbon dots based nanocomposite thin film for highly efficient luminescent solar concentrators

The invention belongs to the technical field of new materials, in particular to an N-CDs/PVP film, a fluorescent solar concentrator with high photoelectric conversion efficiency and a preparation method thereof. N-doped carbon quantum dots are used as fluorescent particles and PVP is used as film forming auxiliary agent. The N-CDs/PVP film UV-Vis has wider absorption range, higher film transmittance, and stronger PL emission light. The fluorescent solar concentrator thus provided has high photoelectric conversion efficiency.

Wang Zijun

Papers

Carbon dots based nanocomposite thin film for highly efficient luminescent solar concentrators

N-CDs/PVP film, fluorescent solar concentrator with high photoelectric conversion efficiency and preparation method thereof