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Colloidal carbon dots (C‐dots) are considered as promising heavy‐metal‐free materials to achieve room‐temperature phosphorescence (RTP) properties for promising applications, such as photoelectronic devices, information encryption, and bio‐imaging. However, most of the current obtained RTP C‐dots have a short lifetime with a relatively low quantum yield (QY). In this work, the C‐dots large‐scale synthesized via a vacuum heating approach have multiple RTP emissions (blue, green, and yellow), a long RTP lifetime of as high as 1.92 s, and a high QY of 34.4% by selecting different types of precursors, which is superior to most of reported RTP C‐dots. The multiple atoms doping and strong bonding between neighbored C‐dots promoted by vacuum heating contributes to the excellent RTP properties. As a proof‐of‐concept, the as‐obtained RTP C‐dots are used as optical ink for flexible security codes, exhibiting a bright shape with a lifetime of 1.37 s. This work offers an efficient approach for producing large‐scale high‐quality RTP C‐dots, which can be applied to anti‐counterfeiting and information encryption systems. [ABSTRACT FROM AUTHOR]

Carbon dots (C-dots) have excellent optical properties and serve as optical building blocks for various potential applications. However, the origin of the double emission in C-dots is still unclear. It is highly desirable to understand deeply the exciton dynamics in double-emission C-dots on the picosecond time scale. Herein, for the first time, double-emission boron-doped carbon dots (B–C-dots) are synthesized with a quantum yield as high as 41.1%. The B–C-dots have an excitation-dependent quantum yield and photoluminescent spectrum. Compared to one dominant energy state in undoped C-dots, B–C-dots exhibited multiple energy states, as proved by femtosecond transient absorption spectroscopy. The controllable double emissions advance the design of a high-level anticounterfeiting code. As a proof-of-concept, by the combination of single-emission and double-emission C-dots, we produced a highly bright excitation-dependent photoluminescence code, showing the great potential for anticounterfeiting systems. [ABSTRACT FROM AUTHOR]

We report the effect of the integration of carbon dots (Cdots) in high-performance inverted planar-heterojunction (PHJ) perovskite solar cells (PSCs). We used Cdots to modify the hole-transport layer in planar PSC devices. By introducing Cdots on graphene oxide (GO) as hole-transporting layer, the efficiency of the PSC improved significantly from 14.7% in the case of bare GO to 16.2% of the best device with optimized Cdots content. When applying Cdots with an engineered absorption in the UV range as downshifting layer, the device performance was further improved, attaining a maximum PCE of 16.8% (+14%); the stability of the device was also enhanced of more than 20%. Kelvin probe force microscopy (KPFM) and cyclic voltammetry (CV) were employed to analyze the electronic band alignment at the interface between GO/Cdots and the perovskite film. Holes were extracted and transferred to the conductive substrate more efficiently in the presence of Cdots, thus delaying charge recombination. Photoluminescence (PL), transient PL decays and transient photovoltage (TPV) decays investigated the charge-transfer kinetics and proved the retardation of charge recombination. This work reveals an effective enhancement of the performance of planar PSCs by using Cdots/GO as hole transport material. Image 1 • Carbon Dots hybrid material is used in place of PEDOT:PSS as hole transporting material. • UV-Absorbing Carbon Dots is used as downshifting layer to improve the efficiency and the long term stability of the device. • The efficiency improved significantly from 14.7% to 16.8% of the best device with optimized Cdots content. • The presence of Cdots on graphene oxide increases the rate of hole injection and decreases charge recombination. [ABSTRACT FROM AUTHOR]

Colloidal Carbon dots (C-dots) have been used as promising emitters for luminescent solar concentrators (LSCs) due to its high quantum yield, low-cost, non-toxic and simple synthetic method. While it is still very challenging to fabricate high-efficiency LSCs based on C-dots because of strong spectral overlap between the absorption and emission. It is still unclear how the refractive index of the C-dots layer affects the optical properties of LSCs. Here we used liquid junction LSCs as an example to investigate the refractive index effect. A large-area (∼100 cm2) LSC was fabricated by injecting C-dots/polyvinylpyrrolidone solution into a glass mold. The refractive index of the polymer solution can be well controlled in the range of 1.33–1.44 by simply enhancing the polymer concentration. The reabsorption energy loss and the optical efficiency of the LSCs are strongly dependent on the refractive index of the polymer solution. The LSC based on C-dots/polymer exhibits refractive index dependent optical efficiency, as high as ∼0.92% under sunlight illumination, which is 27% enhancement in efficiency over the LSC based on C-dots dispersed in methanol. [ABSTRACT FROM AUTHOR]

Luminescent solar concentrator (LSC) can serve as large-area sunlight collectors, suitable for applications in building-integrated high-efficiency and low-cost photovoltaics. Inorganic perovskite quantum dots (QDs) are promising candidates as absorbers/emitters in LSCs, due to their high quantum yields (close to 100%), possibility of tuning size and chemical composition and broad absorption spectrum and high absorption coefficient. However, despite their great potential for technological development, LSCs fabricated using colloidal perovskite QDs still face major challenges such as low optical efficiency and limited long-term stability. Here we report a large-area (~ 100 cm 2 ) tandem LSC based on nearly reabsorption-free carbon dots (C-dots) and inorganic mixed-halide perovskite QDs spectrally-tuned for optimal solar-spectrum splitting. The as-fabricated semi-transparent device, without involving any complicated processes, exhibits an external optical efficiency of ~ 3% under sunlight illumination (100 mW/cm 2 ), which represents a 27% enhancement in efficiency over single layer LSCs based on CsPb(Br x I 1-x ) 3 QDs and 117% over CsPb(Cl x Br 1-x ) 3 QDs. Our work shows that the addition of C-dots can dramatically enhance the long-term durability of LSC devices based on perovskite QDs due to their excellent photostability and simultaneous absorption of ultraviolet light. [ABSTRACT FROM AUTHOR]

Luminescent solar concentrators (LSCs) can serve as large-area sunlight collectors for photovoltaic (PV) cells, reducing the cost of PV generated power. Typical LSCs consist of optical waveguides doped with highly emissive fluorophores e.g. quantum dots (QDs) or dyes/polymers which are required to exhibit high optical efficiency and long-term stability. Compared to conventional fluorophores, carbon dots (C-dots) have superior advantages of non-toxicity, environmental friendliness, low-cost and simple preparation using abundant carbon based feedstock. Here, we demonstrate large-area LSCs (up to 100 cm 2 ) using colloidal C-dots. Two types of LSCs were fabricated by either incorporating oil-soluble oleylamine-treated C-dots into photo-polymerized poly(lauryl methacrylate) (PLMA) or spin-coating the water-soluble C-dots/polyvinylpyrrolidone (PVP) mixture on the glass substrate. LSCs based on C-dots/PLMA exhibit a quantum efficiency of 4% (geometric (G) factor of 38) and an optical efficiency of 1.1% (100 cm 2 , G factor of 12.5) of tandem thin-film LSCs based on C-dots/PVP was achieved under one sun illumination. This performance is comparable to those of LSCs based on inorganic QDs with similar G factor. The LSCs based on C-dots are highly air-stable without any noticeable variation in photoluminescence under ultraviolet illumination (1.3 W/cm 2 ) for over 12 h. [ABSTRACT FROM AUTHOR]