| 1. |
- Han, Yi, et al.
(författare)
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Red and green-emitting biocompatible carbon quantum dots for efficient tandem luminescent solar concentrators
- 2021
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 9:36, s. 12255-12262
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Ahdikari, Rajesh, et al.
(författare)
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High Efficiency, Pt-free Photoelectrochemical Cells for Solar Hydrogen Generation based on “Giant” Quantum Dots
- 2016
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 27, s. 265-274
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Tidskriftsartikel (refereegranskat)abstract
- Quantum dot (QD) sensitized TiO2 is considered as a highly promising photoanode material for photoelectrochemical (PEC) solar hydrogen production. However, due to its limited stability, the photoanode suffers from degradation of its long-term PEC performance. Here, we report the design and characterization of a high-efficiency and long-term stable Pt-free PEC cell. The photoanode is composed of a mesoporous TiO2 nanoparticle film sensitized with “giant” core@shell QDs for PEC solar hydrogen generation. The thick shell enhances light absorption in the visible range, increases the stability of the QDs and does not inhibit charge separation, injection and transport, needed for proper operation of the device. We prepared thin films of Cu2S nanoflakes through a simple and reproducible procedure, and used them as counter-electrodes replacing the standard Pt film, resulting in equivalent performances of the PEC cell. We obtained an unprecedented photocurrent density (~10 mA/cm2) for “giant” QDs based PEC devices (and corresponding H2 generation) and a very promising stability, indicating that the proposed cell architecture is a good candidate for long-term stable QD-based PEC solar hydrogen generation.
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| 3. |
- Alberoni, Chiara, et al.
(författare)
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Ceria doping boosts methylene blue photodegradation in titania nanostructures
- 2021
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Ingår i: Materials Chemistry Frontiers. - : Royal Society of Chemistry. - 2052-1537. ; 5:11, s. 4138-4152
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Tidskriftsartikel (refereegranskat)abstract
- Ceria-doped titania photocatalysts (ceria loading 0.25–5.0 wt%) were synthesized by hydrothermal methods for water remediation. Nanotubes (CeTNTx) and nanoparticles (CeTNPx) were obtained. Ceria doping was applied to tune the electronic properties of nanostructured titania, boosting its photocatalytic activity. CeTNT nanostructures contained anatase as the only titania phase, whereas the CeTNP series consisted of both anatase and rutile polymorphs. The Ce addition induced a decrease in the energy gap, allowing enhancement of visible light harvesting. The photodegradation of methylene blue, MB, in aqueous solution was chosen to study the influence of the morphology and the ceria loading on the photocatalytic response, under UV and solar light. Both CeO2–TiO2 nanoparticles and nanotubes were found to be very active under UV light. The highest MB degradation rates were obtained for the 0.25 wt% CeO2 doping, for both nanotubes and nanoparticles (0.123 and 0.146 min−1, respectively), able to photodegrade completely the dye after 120 min. The two samples are stable after a 3-cycle reusability test. The photo-response under simulated solar light confirmed that doping titania with ceria allows harvesting visible light absorption, enhancing its photoactivity. A maximum efficiency of 85% under simulated sunlight at a degradation rate of 0.054 min−1 was obtained. Transient photoluminescence confirmed that MB acts as a charge scavenger for the composite system. These results pointed out ceria-doped titania nanostructures as a promising class of photocatalysts for the degradation of dyes and other hazardous organic compounds in wastewater.
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| 4. |
- Basu, Kaustubh, et al.
(författare)
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Enhanced photovoltaic properties in dye sensitized solar cells by surface treatment of SnO2 photoanodes
- 2016
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- We report the fabrication and testing of dye sensitized solar cells (DSSC) based on tin oxide (SnO2) particles of average size ~20 nm. Fluorine-doped tin oxide (FTO) conducting glass substrates were treated with TiOx or TiCl4 precursor solutions to create a blocking layer before tape casting the SnO2 mesoporous anode. In addition, SnO2 photoelectrodes were treated with the same precursor solutions to deposit a TiO2 passivating layer covering the SnO2 particles. We found that the modification enhances the short circuit current, open-circuit voltage and fill factor, leading to nearly 2-fold increase in power conversion efficiency, from 1.48% without any treatment, to 2.85% achieved with TiCl4 treatment. The superior photovoltaic performance of the DSSCs assembled with modified photoanode is attributed to enhanced electron lifetime and suppression of electron recombination to the electrolyte, as confirmed by electrochemical impedance spectroscopy (EIS) carried out under dark condition. These results indicate that modification of the FTO and SnO2 anode by titania can play a major role in maximizing the photo conversion efficiency
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| 5. |
- Benetti, Daniele, et al.
(författare)
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Direct Measurement of Electronic Band Structure in Single Quantum Dots of Metal Chalcogenide Composites
- 2018
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Ingår i: Small (Weinheim an der Bergstrasse, Germany). - : John Wiley & Sons. - 1613-6810 .- 1613-6829. ; 14:51
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Tidskriftsartikel (refereegranskat)abstract
- Metal chalcogenide quantum dots (QDs) are among the most promising materials as light harvesters in all-inorganic systems for applications in solar cells and production of solar fuels. The electronic band structure of composite QDs formed by lead and cadmium chalcogenides directly grafted on highly oriented pyrolytic graphite surfaces through successive ionic layer absorption and reaction is investigated. Atomic force microscopy and Kelvin probe force microscopy (KPFM) are applied to investigate PbS, CdS, and PbS/CdS QD systems. The variation of the surface potential of individual QDs is measured, investigating the evolution of the electronic band structure as a function of QD size and composition. A shift of the Fermi level toward more negative values occurs when QD size is increased. The shift is more pronounced in CdS than in PbS, while the composite PbS/CdS exhibits an intermediate behavior. The calculated shift is in good agreement with the experiments. These results highlight the ability of KPFM to directly measure the electronic band structure in individual QDs of metal chalcogenide composites. This feature regulates charge dynamics in composite systems, thereby affecting device performance. This work provides valuable insights for applications in several fields, in which charge injection plays a major role.
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| 6. |
- Benetti, Daniele, et al.
(författare)
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Functionalized multi-wall carbon nanotubes/TiO2 composites as efficient photoanodes for dye sensitized solar cells
- 2016
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Ingår i: Journal of Materials Chemistry C. - 2050-7526 .- 2050-7534. ; 4:16, s. 3555-3562
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Benetti, Daniele, et al.
(författare)
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Hole-extraction and photostability enhancement in highly efficient inverted perovskite solar cells through carbon dot-based hybrid material
- 2019
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 62, s. 781-790
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Fanizza, Elisabetta, et al.
(författare)
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Encapsulation of Dual Emitting Giant Quantum Dots in Silica Nanoparticles for Optical Ratiometric Temperature Nanosensors
- 2020
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 10:8
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Tidskriftsartikel (refereegranskat)abstract
- Accurate temperature measurements with a high spatial resolution for application in the biomedical fields demand novel nanosized thermometers with new advanced properties. Here, a water dispersible ratiometric temperature sensor is fabricated by encapsulating in silica nanoparticles, organic capped PbS@CdS@CdS “giant” quantum dots (GQDs), characterized by dual emission in the visible and near infrared spectral range, already assessed as efficient fluorescent nanothermometers. The chemical stability, easy surface functionalization, limited toxicity and transparency of the silica coating represent advantageous features for the realization of a nanoscale heterostructure suitable for temperature sensing. However, the strong dependence of the optical properties on the morphology of the final core–shell nanoparticle requires an accurate control of the encapsulation process. We carried out a systematic investigation of the synthetic conditions to achieve, by the microemulsion method, uniform and single core silica coated GQD (GQD@SiO2) nanoparticles and subsequently recorded temperature-dependent fluorescent spectra in the 281-313 K temperature range, suited for biological systems. The ratiometric response—the ratio between the two integrated PbS and CdS emission bands—is found to monotonically decrease with the temperature, showing a sensitivity comparable to bare GQDs, and thus confirming the effectiveness of the functionalization strategy and the potential of GQD@SiO2 in future biomedical applications.
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| 9. |
- Han, Yi, et al.
(författare)
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Highly efficient ratiometric nanothermometers based on colloidal carbon quantum dots
- 2021
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Ingår i: Journal of materials chemistry. B. - : Royal Society of Chemistry. - 2050-750X .- 2050-7518. ; 9:20, s. 4111-4119
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Tidskriftsartikel (refereegranskat)abstract
- Optical nanothermometers have attracted much attention due to their non-contact and precise measurement with high spatial resolution at the micro- and nanoscales. They can be applied in various fields such as micro-opto-electronics, photonics, and biomedical thermal and pH sensing, while most thermal sensors reported so far contain heavy metals or have low sensitivity. Herein, we demonstrate a highly sensitive ratiometric thermal sensor based on colloidal C-dots. C-dots exhibit dual emission originating from the band gap emission and surface-dominant emission, which show a different temperature-dependent photoluminescence (PL) response. Among different surface-functionalized C-dots, C-dots@OH exhibit an absolute thermal sensitivity of -0.082 degrees C-1, which is the highest among various types of ratiometric thermosensors, making it a very promising candidate for high-sensitivity, self-calibrated nanoscale thermometry. As a proof-of-concept, C-dots@OH were employed to monitor the intracellular temperature (32-42 degrees C), showing a clear trend for temperature variation in a single cell, indicating that C-dots could offer a powerful tool for a potential precise measurement of the intracellular temperature. They could also be used as thermal sensors for nano-electronic and optoelectronic devices.
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| 10. |
- Han, Yi, et al.
(författare)
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Synthesis, optical properties and applications of red/near-infrared carbon dots
- 2022
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 10:33, s. 11827-11847
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Forskningsöversikt (refereegranskat)abstract
- Compared to inorganic quantum dots, fluorescent carbon nanomaterials (C-dots) have gained significant attention because of their unique optoelectrical properties and low toxicity. Although many review articles summarized the last research achievements, only a few of them are focusing on red/near-infrared C-dots. Due to their unique optical and optoelectrical properties in the red/near-infrared region, this interesting subclass of C-dots may be applied as important building blocks for several applications spanning from bioimaging and nano-thermometry, to luminescent solar concentrators (LSCs) and photoelectrochemical systems. Therefore, in this review the synthesis and the fluorescence mechanism together with the most important applications in thermometry, bio-imaging, LSCs and photocatalysis of red/near-infrared C-dots are considered. Furthermore, another aim is to highlight the available approaches to improve the carbonization degree and, additionally, to discuss the structure/composition correlated optical properties. Finally, outlooks, future perspectives and challenges are also discussed for these highly promising nanostructures.
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| 11. |
- Jin, Lei, et al.
(författare)
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Dynamics of semiconducting nanocrystal uptake into mesoporous TiO2 thick films by electrophoretic deposition
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:2, s. 847-856
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Tidskriftsartikel (refereegranskat)abstract
- Electrophoretic deposition (EPD) is a simple technique for the uptake of nanoparticles into mesoporous films, for example to graft semiconducting nanocrystals (quantum dots, QDs) on mesoporous oxide thick films acting as photoanodes in third generation solar cells. Here we study the uptake of colloidal QDs into mesoporous TiO2 films using EPD. We examined PbS@CdS core@shell QDs, which are optically active in the near infrared (NIR) region of the solar spectrum and exhibit improved long-term stability toward oxidation compared to their pure PbS counterpart, as demonstrated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. We applied Rutherford backscattering spectrometry (RBS) to obtain the Pb depth profile into the TiO2 matrix. EPD duration in the range from 5 to 120 min and applied voltages from 50 to 200 V were considered. The applied electric field induces the fast anchoring of QDs to the oxide surface. Consequently, QD concentration in the solution contained in the mesoporous film drastically decreases, inducing a Fick-like diffusion of QDs. We modelled the entire process as a QD diffusion related to the formation of a QD concentration gradient, and a depth-independent QD anchoring, and were able to determine the electric field-induced diffusion coefficient D for QDs and the characteristic time for QD grafting, in very good agreement with the experiment. D increases from (1.5 +/- 0.4) x 10(-5) mu m(2) s(-1) at 50 V to (1.1 +/- 0.3) x 10(-3) mu m(2) s(-1) at 200 V. The dynamics of EPD may also be applied to other different colloidal QDs and quantum rod materials for the sensitization of mesoporous films. These results quantitatively describe the process of QD uptake during EPD, and can be used to tune the optical and optoelectronic properties of composite systems, which determine, for instance, the photoconversion efficiency in QD solar cells (QDSCs).
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| 12. |
- Jin, Lei, et al.
(författare)
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Engineering Interfacial Structure in “Giant” PbS/CdS Quantum Dots for Photoelectrochemical Solar Energy Conversion
- 2016
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 30, s. 531-541
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial structure in “giant” PbS/CdS quantum dots (QDs) was engineered by modulating the Cd:S molar ratio during in situ growth. The control of the gradient interfacial layer could facilitate hole transfer, regulate the transition from double- to single-color emission, as a consequence. These QDs are optically active close-to-the near-infrared (NIR) spectral region and are candidates as absorber materials in solar energy conversion. Photoinduced charge transfer from “giant” QDs to electron scavenger can still take place despite the ultra-thick (~5 nm) shell. The hybrid architecture based on a TiO2 mesoporous framework sensitized by the “giant” QDs with alloyed interface can produce a saturated photocurrent density as high as ~5.3 mA/cm2 in a photoelectrochemical (PEC) cell under 1 Sun illumination, which is around 2 times higher than that of bare PbS and core/thin-shell PbS/CdS QDs sensitizer. The as-prepared PEC device presented very good stability thanks to the “giant” core/shell QDs architecture with tailored interfacial layer and a further coating of the ZnS shell. 78% of the initial current density is kept after 2-hour irradiation at 1 Sun. Engineering of electronic band structure plays a key role in boosting the functional properties of these composite systems, which hold great potential for H2 production in PEC devices.
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| 13. |
- Jin, Lei, et al.
(författare)
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Near-Infrared Colloidal Quantum Dots for Efficient and Durable Photoelectrochemical Solar-Driven Hydrogen Production
- 2016
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Ingår i: Advanced Science. - : Wiley. - 2198-3844. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- A new hybrid photoelectrochemical photoanode is developed to generate H2 from water. The anode is composed of a TiO2 mesoporous frame functionalized by colloidal core@shell quantum dots (QDs) followed by CdS and ZnS capping layers. Saturated photocurrent density as high as 11.2 mA cm−2 in a solar-cell-driven photoelectrochemical system using near-infrared QDs is obtained.
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| 14. |
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| 15. |
- Li, Weihua, et al.
(författare)
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Controllable and large-scale synthesis of carbon quantum dots for efficient solid-state optical devices
- 2024
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Ingår i: Nano Energy. - : Elsevier Ltd. - 2211-2855 .- 2211-3282. ; 122
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Tidskriftsartikel (refereegranskat)abstract
- Carbon quantum dots (C-dots) showed excellent structure-tunable optical properties, mainly composed of carbon, nitrogen and oxygen. They have been used for various types of solid-state optical devices. Due to the photoluminescence quenching caused by aggregation, it is a challenge to produce high quantum yield and large Stokes shift C-dots via controllable and simple approaches. In this work, we demonstrated a microwave assisted heating approach for the high-quality C-dots production with ten grams scale per batch in less than 4 min. The addition of metal cation promoted the formation of the foam-structure by forming carboxyl-metal-amine complex, enabling the spatial confined growth of the C-dots in a solid-state, contributing to the high quantum yield (QY) of 73% with a Stokes shift of 0.65 eV. By tuning the structure of the C-dots, excitation dependent and independent photoluminescent (PL) behavior were achieved because of the formation of the different types of energy states evidenced by transient PL and femtosecond transient absorption spectroscopy. These optical properties enable the C-dots to be successfully integrated in luminescent solar concentrators (LSCs), having an external optical efficiency of 3.0% and a power conversion efficiency of 1.3% (225 cm2) and an excitation-dependent high-level anticounterfeiting fluorescent code, showing a great potential for solid-state optical system.
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| 16. |
- Liang, Hongyan, et al.
(författare)
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Silver Nanorice Structures: Oriented Attachment-Dominated Growth, High Environmental Sensitivity, and Real-Space Visualization of Multipolar Resonances
- 2012
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 24:12, s. 2339-2346
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Tidskriftsartikel (refereegranskat)abstract
- We have synthesized and investigated the anisotropic growth of interesting silver nanorice. Its growth is kinetically controlled at 100 degrees C, and both oriented attachment and Ostwald ripening are involved, with the former growth mode dominating the anisotropic growth of the nanorice along the < 111 > direction. This one-directional growth is initiated by an indispensable seed-selection process, in which oxygen plays a critical role in oxidatively etching twinned silver crystals. The inhibition of this process by removing oxygen essentially blocks the nanorice growth. Although increasing reaction temperature to 120 degrees C accelerates the one-dimensional growth along the < 111 > direction, further temperature increase to 160 degrees C makes the oriented attachment dominated one-directional growth disappear; instead, the diffusion-controlled two-dimensional growth leads to the emergence of highly faceted truncated triangular and hexagonal plates mainly bound by low energy faces of {111}. Interestingly, we also found that the longitudinal surface plasmon resonance of the nanorice structures is highly sensitive to the refractive index of surrounding dielectric media, which predicts their promising applications as chemical or biological sensors. Moreover, the multipolar plasmonic resonances in these individual nanorice structures are visualized in real space, using high-resolution electron energy-loss spectroscopy.
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| 17. |
- Liu, Guiju, et al.
(författare)
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High efficiency sandwich structure luminescent solar concentrators based on colloidal quantum dots
- 2019
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 60, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- Luminescent solar concentrators (LSCs) have received significant attention because of their low cost, large-area and high efficiency sunlight energy harvesting. Colloidal core/shell quantum dots (QDs) are promising candidates as absorbers/emitters in LSCs. However, due to the limitation of QDs properties and device architectures, LSCs fabricated using QDs still face the challenges of low optical efficiency and limited long-term stability for the large-area LSCs. In this work, we synthesized CdSe/CdS QDs, and found that higher CdS shell growth temperature results in improved uniformity in structure and morphology and more suitable optical properties. Based on the CdSe/CdS QDs, a large-area (∼100 cm 2 ) sandwich structure luminescent solar concentrator (LSC) was fabricated. By laminating the QDs layer between two sheets of optical clear glass, the reabsorption losses of the device can be reduced due to the decrease of photon escape. The as-fabricated sandwich structure device exhibits an external optical efficiency of ∼ 2.95% under natural sunlight illumination, which represents a 78% enhancement in efficiency over the single layer film LSCs based on CdSe/CdS QDs. More importantly, the sandwich structure can protect the QDs interlayer from the impact of the ambient environment (e.g. oxygen, moisture and alkalinity) and enhance the long-term stability of LSCs. Our work shows that the use of suitably tuned core-shell QDs and the sandwich structure in LSC architecture can dramatically enhance the external optical efficiency of LSC devices based on CdSe/CdS QDs.
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| 18. |
- Liu, Guiju, et al.
(författare)
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Red-emissive carbon quantum dots enable high efficiency luminescent solar concentrators
- 2023
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 11:16, s. 8950-8960
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Tidskriftsartikel (refereegranskat)abstract
- Luminescent solar concentrators (LSCs) are large-area sunlight collectors for efficient solar-to-electricity conversion. The key point for highly efficient LSCs is the choice of fluorophores, which need to have broad absorption, high quantum yield and large Stokes shift. Among various fluorophores, carbon quantum dots (C-dots) hold great promise as eco-friendly alternatives to heavy-metal-containing quantum dots (QDs) due to their adjustable absorption and emission spectra, non-toxicity, low cost and eco-friendly synthetic methods. However, due to the limited absorption band and relatively low quantum yield in the red region, it is a challenge to obtain efficient LSCs based on C-dots. Here, we demonstrated highly efficient LSCs based on red-emissive C-dots. The as-synthesized C-dots have a cubic structure, broad absorption covering 300-600 nm, and red emission (peak located at 595 nm), with a high quantum yield of ∼65% and a large Stokes shift of 0.45 eV. Transient absorption experiments of the C-dots revealed the ultrafast formation of the broad emissive state (1 ps). Based on the excellent optical properties of the C-dots, the as-prepared large-area LSC (10 × 10 × 0.52 cm3) exhibited an optimized external optical efficiency of 4.81% and a power conversion efficiency of 2.41% under natural sun irradiation (70 mW cm−2). Furthermore, a tandem LSC using green-emissive C-dots (top layer) and red-emissive C-dots (bottom layer) as fluorophores exhibited an external optical efficiency as high as 6.78%. These findings demonstrate the possibility of using eco-friendly carbon-based nanomaterials for highly efficient large-area LSCs.
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| 19. |
- Liu, Guiju, et al.
(författare)
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Role of refractive index in highly efficient laminated luminescent solar concentrators
- 2020
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 70
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Tidskriftsartikel (refereegranskat)abstract
- As a large-area solar radiation collector, luminescent solar concentrators (LSCs) can be used as power generation units in semitransparent solar windows, modernized agricultural greenhouses and building facades. However, the external optical efficiency and long-term stability of the LSCs limit their practical applications due to the sensitivity of the emitters to the light and environmental conditions. Here, we used the concept of “laminated glass” to prepare LSCs, which consist of two waveguide layers and the quantum dots (QDs)/polymer interlayer, and we tune the refractive index of the different parts of the system to improve the external optical efficiency and stability of the LSCs, simultaneously. The waveguide layer can be glass, quartz, polymethyl methacrylate (PMMA) and other transparent materials. The CdSe/CdS core/shell QDs were used as fluorophores to prepare the interlayer of the LSCs. The external optical efficiency of the laminated LSCs is associated with the refractive index of the three layers: the closer the refractive index, the higher the ηopt. The highest external optical efficiency of 3.4% has been achieved for the laminated PMMA/QDs-polymer/PMMA LSCs, which improved ~92% compared to the single-layered CdSe/CdS based LSCs. To the best of our knowledge, this is the highest efficiency for the LSCs based on CdSe/CdS QDs. These results pave the way to realize high efficiency laminated windows as power generation units by suitably tuning the structure of the LSC, and provide the theoretical guidance for the LSCs utilized in building integrated photovoltaics.
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| 20. |
- López-Delgado, R., et al.
(författare)
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Enhanced conversion efficiency in Si solar cells employing photoluminescent down-shifting CdSe/CdS core/shell quantum dots
- 2017
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Silicon solar cells have captured a large portion of the total market of photovoltaic devices mostly due to their relatively high efficiency. However, Silicon exhibits limitations in ultraviolet absorption because high-energy photons are absorbed at the surface of the solar cell, in the heavily doped region, and the photo-generated electron-hole pairs need to diffuse into the junction region, resulting in significant carrier recombination. One of the alternatives to improve the absorption range involves the use of down-shifting nano-structures able to interact with the aforementioned high energy photons. Here, as a proof of concept, we use downshifting CdSe/CdS quantum dots to improve the performance of a silicon solar cell. The incorporation of these nanostructures triggered improvements in the short circuit current density (Jsc, from 32.5 to 37.0 mA/cm2). This improvement led to a ∼13% increase in the power conversion efficiency (PCE), from 12.0 to 13.5%. Our results demonstrate that the application of down-shifting materials is a viable strategy to improve the efficiency of Silicon solar cells with mass-compatible techniques that could serve to promote their widespread utilization.
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| 21. |
- López-Delgado, R., et al.
(författare)
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Influence of photo-luminescent CdSe/CdS core shell quantum dots in solar cell efficiency
- 2016
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 773:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis and characterization of CdSe/CdS core-shell quantum dots (CdSe/CdS-QDs) that exhibit absorption in the UV range of the solar spectrum and emit photons with wavelengths centered around 625 nm, a wavelength that is well suited for silicon absorption and electron-hole pair generation. We also report the fabrication and characterization of single crystal silicon (c-Si) solar cells with and without the aforementioned photo luminescent, down-shifting CdSe/CdS- QDs. The incorporation of these nanostructures triggered improvements in the performance of the devices, particularly in the open circuit voltage (Voc) and short circuit current density (Jsc) for which the measured values showed an increase from 543 to 546 mV and from 32.5 to 37.0 mA/cm2, respectively. The combined effect of the improved values led to an increment in the power conversion efficiency (PCE) from 12.01 to 13.54%. This increase represents a 12.7% improvement in the PCE of the fabricated devices. The effort described herein is considered a good fit to the generalized trend to improve the efficiency of solar cells with mass-compatible techniques that could serve to promote their widespread utilization
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| 22. |
- Navarro Prado, F., et al.
(författare)
-
Nanofiber-Structured TiO2 Nanocrystals as a Scattering Layer in Dye-Sensitized Solar Cells
- 2017
-
Ingår i: ECS Journal of Solid State Science and Technology. - : Electrochemical Society. - 2162-8769 .- 2162-8777. ; 6:4
-
Tidskriftsartikel (refereegranskat)abstract
- We developed a scattering layer composed of TiO2 nanocrystals assembled into a densely packed three-dimensional network of nanofibers to localize light within a photoanode used in dye sensitized solar cells (DSSCs). The electro-netting approach was applied to obtain polyamide 6 nanofibers with bi-modal diameter distribution, followed by solvothermal synthesis for the coating of TiO2 nanocrystals on the polymer template. The resulting nanofiber-structured scattering layer (NFSL) is composed of TiO2 nanofibers (200-300 nm in diameter) supporting an ultrathin nanofiber network (diameters within 10-50 nm) and exhibits strong light scattering in the visible range (400 to 700 nm). This NFSL was applied on top of a transparent active TiO2 layer (TL) forming the photoanode in DSSCs. The performance of the bi-layered photoanode was compared to its analogue, fabricated with commercial scattering layers containing different sizes of nanoparticles. The DSSCs assembled with the NFSL showed an 18% enhancement in power conversion efficiency (PCE) compared to that of DSSCs whose photoanode contained only a TL. This enhancement factor was improved up to 31% when the bi-layered structure was post-treated with TiCl4. The PCE improvement was mainly associated with the light harvesting efficiency within the photoanode because of scattering from the NFSL and increased dye adsorption due to the addition of this top layer. These conclusions were inferred from diffuse reflectance behavior, dye loading measurements, external quantum efficiency and electrochemical properties. Our work demonstrates a promising approach without the requirement of time consuming and complicated procedures for the fabrication of a densely packed 3D nanofiber network scattering layer for diverse energy conversion devices and photocatalytic applications
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| 23. |
- Navarro Prado, F., et al.
(författare)
-
Platinum/Palladium hollow nanofibers as high-efficiency counter electrodes for enhanced charge transfer
- 2016
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 335, s. 138-145
-
Tidskriftsartikel (refereegranskat)abstract
- Pt/Pd hollow nanofibers were obtained by sputtering a Pt/Pd alloy (80/20 wt%) onto polymer nanofibers (used as sacrificial template) and were used as counter-electrodes (CEs) in dye-sensitized solar cells (DSSCs). We demonstrate that optimization of nanofiber density and Pt/Pd sputtering thickness can increase the short circuit current density and consequently lead to a ∼15% enhancement in power conversion efficiency (PCE), when compared to the commonly used flat Pt/Pd CEs with the same thickness. The processes that contribute to such PCE improvement are: (i) increased surface area provided by the high aspect ratio hollow nanofibers and (ii) improved electro-catalytic performance, as validated by electrochemical impedance spectroscopy (EIS) measurements. The latter showed a two-fold decrease in the charge-transfer resistance of the nanostructured-CE, compared to the flat CE. The contribution of the Pt/Pd hollow nanofiber to light scattering was negligible as shown by reflectance measurements. These results suggest a simple and straightforward strategy to increase PCE in DSSCs, to minimize the use of precious metals used in this kind of devices and, more generally, to tailor the CE structure in photoelectrochemical systems to boost their functional properties, thanks to the advantages afforded by this complex morphology.
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| 24. |
- Ren, Shihuan, et al.
(författare)
-
Near-infrared heavy-metal-free SnSe/ZnSe quantum dots for efficient photoelectrochemical hydrogen generation
- 2021
-
Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 13:6, s. 3519-3527
-
Tidskriftsartikel (refereegranskat)abstract
- Solar-driven photoelectrochemical (PEC) hydrogen production is one of the most effective strategies for solar-to-hydrogen energy conversion. Among various types of semiconductors used for PEC anodes, colloidal quantum dots (QDs) have been widely used as new and promising absorbers for PEC and other optoelectronic devices. However, currently, most efficient optoelectronic devices contain toxic Pb/Cd elements or non-earth-abundant elements (In/Ag). It is still a challenge to produce Pb/Cd-free QDs without using any toxic and non-earth-abundant elements. Here, we synthesized SnSe QDs via a diffusion-controlled hot injection approach and further stabilized the as-prepared SnSe QDs via a cation exchange reaction. The as-synthesized Zn-stabilized SnSe QDs (SnSe/ZnSe) have an orthorhombic crystal structure with indirect bandgaps ranging from 1 to 1.37 eV. Zn stabilization can significantly decrease the number of QD surface metallic Sn bonds, thereby decreasing the number of recombination centers of defects/traps. As a proof-of-concept, SnSe/ZnSe QDs are used as light absorbers for PEC hydrogen production, leading to a saturated photocurrent density of 7 mA cm−2, which is comparable to best values reported for PEC devices based on toxic-metal-free QDs. Our results indicate that Zn-stabilized SnSe QDs have great potential for use in emerging optoelectronic devices.
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| 25. |
- Sirigu, Gianluca, et al.
(författare)
-
Dual emission and optical gain in PbS/CdS nanocrystals : Role of shell volume and of core/shell interface
- 2017
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 96:15
-
Tidskriftsartikel (refereegranskat)abstract
- Colloidal semiconductor nanocrystals (NCs) emitting simultaneously at two distinct wavelengths are of great interest for multiple applications ranging from ultrasensitive self-calibrating nanoscale sensing to light-emitting diodes and white-light emission. The physical mechanism governing dual emission in core/shell NCs composed of two materials is still under investigation; in particular, the roles of the volume of the shell and of the core/shell interface are not well understood. Here we compare three different PbS/CdS NCs with identical cores, but shells of different thicknesses and different core/shell interfaces. We study photoluminescence (PL) characteristics and ultrafast exciton dynamics with subpicosecond time resolution. We find that dual emission is possible for both thick and thin quantum-confined shells, and for different core/shell interfaces. We show that very thick shells allow the decoupling of shell excitons from core ones and we fully describe the dynamic exciton barrier, connected to efficient shell PL. We discuss the efficiency of shell PL in relation to the properties of the NCs and show that it can give rise to optical gain. Our results provide a comprehensive understanding of the physical phenomena governing dual-emission mechanisms in NCs.
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| 26. |
- Sirigu, Gianluca, et al.
(författare)
-
Ultrafast exciton dynamics in doubly emitting asymmetric giant PbS/CdS/CdS Nanocrystals
- 2015
-
Konferensbidrag (refereegranskat)abstract
- Semiconductor nanocrystals (NCs) are interesting optical materials that have been explored for a range of applications such as light emitting diodes (LEDs), photovoltaic cells, lasers and biologic markers. For practical optical uses heterostructured NCs with thick shells (“giant NCs”) offer the advantage of supressed photoluminescence intermittency and reduced rates of Auger recombination. Giant NCs with proper structures can present simultaneous two-colour emission, due to core and shell states [1-2]. These NCs can be convenient for example in very accurate and self-calibrating nanosystems.
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| 27. |
- Tong, Xin, et al.
(författare)
-
Heavy Metal-free, Near-infrared Colloidal Quantum Dots for Efficient Photoelectrochemical Hydrogen Generation
- 2017
-
Ingår i: Nano Energy. - : Elsevier. - 2211-2855. ; 31, s. 441-449
-
Tidskriftsartikel (refereegranskat)abstract
- Photoelectrochemical (PEC) hydrogen generation based on colloidal quantum dots (QDs) is very promising because of its high solar energy to fuel conversion efficiency and low fabrication costs. However, its commercial development is hindered by various challenges, including the widespread use of toxic heavy metal–based QDs as sensitizers. We report an environmentally friendly, high efficiency PEC device in which the photoanode consists of a mesoporous TiO2 film sensitized with heavy metal-free, near-infrared (NIR) colloidal CuInSexS2-x (CISeS) QDs. To reduce surface-related traps, we grew an ultrathin ZnS shell on the CISeS core QDs by cation exchange. The PEC cell based on this core/shell CISeS/ZnS QDs exhibits suppressed charge recombination and a saturated photocurrent density of ~5.3 mA/cm2 under one sun illumination (AM 1.5 G, 100 mW/cm2). In addition, the as-prepared PEC device shows an outstanding stability, exhibiting a drop of only 23% after 9 h illumination. The success in using such core/shell CISeS/ZnS QDs paves the way to realize environment-friendly, high efficiency and cost-effective PEC devices for hydrogen production.
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| 28. |
- Wang, Rui, et al.
(författare)
-
Environmentally friendly Mn-alloyed core/shell quantum dots for high-efficiency photoelectrochemical cells
- 2020
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 8:21, s. 10736-10741
-
Tidskriftsartikel (refereegranskat)abstract
- Colloidal quantum dot (QD)-based photoelectrochemical (PEC) cells are cost-effective devices showing remarkable solar-to-fuel conversion efficiency. However, the extensive use of highly toxic elements (e.g. Pb and Cd) in QDs' synthesis and device fabrication is still a major challenge towards their practical development. Herein, we fabricate a solar-driven PEC cell based on environmentally friendly Mn-alloyed CuInS2 (MnCIS)/ZnS core/shell QDs, showing more favorable band alignment, efficient charge transfer, reduced charge recombination and lower charge transfer resistance with respect to the control device fabricated using unalloyed CuInS2 (CIS)/ZnS core/shell QDs. An unprecedented photocurrent density of ∼5.7 mA cm−2 with excellent stability was obtained for the as-fabricated MnCIS/ZnS core/shell QD-based PEC device when operated under standard one sun irradiation (AM 1.5G, 100 mW cm−2). These results indicate that the transition metal-alloyed environmentally friendly core/shell QDs are promising for next-generation solar technologies.
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| 29. |
- Wang, Xiaohan, et al.
(författare)
-
Colloidal carbon quantum dots as light absorber for efficient and stable ecofriendly photoelectrochemical hydrogen generation
- 2021
-
Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 86
-
Tidskriftsartikel (refereegranskat)abstract
- Solar-driven hydrogen production is one of the most promising strategies for solar-to-hydrogen energy conversion. Compared to inorganic quantum dots (QDs), carbon quantum dots (C-dots) have attracted a lot of attention for optoelectronic devices due to their structure-dependent optical properties and green composition. However, the solar-to-hydrogen conversion efficiency of most of the photoelectrochemical (PEC) devices based on colloidal QDs is still low. Here we demonstrated a highly efficient and stable ecofriendly PEC device using C-dots sensitized TiO2 photoanode, Pt loaded on carbon nanofibers as counter electrode, and glucose aqueous solution as electrolyte. The red-color C-dots were prepared using a solvothermal reaction, with an absorption spectrum ranging from 300 to 600 nm and a quantum yield (QY) of 50%. The C-dots have excitation independent photoluminescence peak positions and highly crystalline structure. The hydroxyl group on the C-dots can strongly interact with the TiO2, forming a very stable complex. Benefiting from these features, the PEC devices based on C-dots exhibit a saturated photocurrent density as high as ~4 mA/cm2 at 0.6 V vs. RHE and the device is very stable (keeping 95% of its initial value after 10-hour illumination upon 100 mW/cm2). This work indicates the promising properties of the C-dots/TiO2 system, which holds huge potential for applications in the fields of optoelectronic and catalytic devices.
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| 30. |
|
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| 31. |
- Zhao, Haiguang, et al.
(författare)
-
Absorption Enhancement in “Giant” Core/Alloyed-Shell Quantum Dots for Luminescent Solar Concentrator
- 2016
-
Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 12:38, s. 5354-5365
-
Tidskriftsartikel (refereegranskat)abstract
- Luminescent solar concentrators (LSCs) can potentially reduce the cost of solar cells by decreasing the photoactive area of the device and boosting the photoconversion efficiency (PCE). This study demonstrates the application of “giant” CdSe/CdxPb1–xS core/shell quantum dots (QDs) as light harvesters in high performance LSCs with over 1.15% PCE. Pb addition is critical to maximize PCE. First, this study synthesizes “giant” CdSe/CdxPb1–xS QDs with high quantum yield (40%), narrow size distribution (<10%), and stable photoluminescence in a wide temperature range (100–300 K). Subsequently these thick alloyed-shell QDs are embedded in a polymer matrix, resulting in a highly transparent composite with absorption spectrum covering the range 300–600 nm, and are applied as active material for prototype LSCs. The latter exhibits a 15% enhancement in efficiency with respect to 1% PCE of the pure-CdS-shelled QDs. This study attributes this increase to the contribution of Pb doping. The results demonstrate a straightforward approach to enhance light absorption in “giant” QDs by metal doping, indicating a promising route to broaden the absorption spectrum and increase the efficiency of LSCs.
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| 32. |
- Zhao, Haiguang, et al.
(författare)
-
Colloidal thick-shell pyramidal quantum dots for efficient hydrogen production
- 2018
-
Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 53, s. 116-124
-
Tidskriftsartikel (refereegranskat)abstract
- Colloidal semiconductor quantum dots (QDs) have attracted a great attention for their potential applications in optoelectronic devices, such as water splitting, luminescent solar concentrators, and solar cells, because of their size/shape/composition-dependent optoelectronic properties. However, the fast electron-hole (e-h) recombination and slow charge separation of QDs limit their applications as light absorbers in high-efficiency optoelectronic devices. Here, we synthesized thick-shell CdSe/CdSexS1-x/CdS QDs with pyramidal shape, which exhibit a quantum yield of ~ 15%, with a long radiative lifetime up to ~ 100 ns due to the spatial separation of the e/h wavefunction and significantly broadened light absorption toward the 500–700 nm range, compared to CdSe/CdS unalloyed QDs. As a proof-of-concept, the pyramidal QDs are applied as light absorbers in a photoelectrochemical (PEC) system, leading to a saturated photocurrent density of ~ 12 mA/cm2 (with a H2 generation rate of 90 mL cm−2 day−1), which is a record for thick-shell QD-based photoelectrodes in PEC hydrogen generation. Core/thick-shell QDs hold great potential for breakthrough developments in the field of QD-based optoelectronic devices.
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| 33. |
- Zhao, Haiguang, et al.
(författare)
-
Dual emission in Asymmetric “Giant” PbS/CdS/CdS Core/Shell/Shell Quantum Dots
- 2016
-
Ingår i: Nanoscale. - 2040-3364 .- 2040-3372. ; 8:7, s. 4217-4226
-
Tidskriftsartikel (refereegranskat)abstract
- Semiconducting nanocrystals optically active in the infrared region of the electromagnetic spectrum enable exciting avenues in fundamental research and novel applications compatible with the infrared transparency windows of biosystems such as chemical and biological optical sensing, including nanoscale thermometry. In this context, quantum dots (QDs) with double color emission may represent ultra-accurate and self-calibrating nanosystems. We present the synthesis of giant core/shell/shell asymmetric QDs having a PbS/CdS Zincblende (Zb)/CdS Wurtzite (Wz) structure with double color emission close to the near-infrared (NIR)region. We show that the double emission depends on the excitation condition and analyze the electron-hole distribution responsible of the independent and simultaneous radiative exciton recombination in the PbS core and in the CdS Wz shell, respectively. These results highlight the importance of the driving force leading to preferential crystal growth in asymmetric QDs, and provide a pathway for a rational control of the synthesis of double color emitting giant QDs, leading to the effective exploitation of visible/NIR transparency windows.
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| 34. |
- Zhao, Haiguang, et al.
(författare)
-
Gram-scale synthesis of carbon quantum dots with a large Stokes shift for the fabrication of eco-friendly and high-efficiency luminescent solar concentrators
- 2021
-
Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry. - 1754-5692 .- 1754-5706. ; 14:1, s. 396-406
-
Tidskriftsartikel (refereegranskat)abstract
- 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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| 35. |
- Zhao, Haiguang, et al.
(författare)
-
Green synthesis of near infrared core/shell quantum dots for photocatalytic hydrogen production
- 2016
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 27:49
-
Tidskriftsartikel (refereegranskat)abstract
- Quantum dots (QDs) are attractive systems for potential applications in future solar energy technologies, due to their optical properties which are tunable as a function of size and composition. In this study, we synthesized PbS QDs with first excitonic peak in the range 1060 to 1300 nm using a PbCl2/sulfur molar ratio of 10:1. The first excitonic absorption peak from 1300 to 950 nm of the PbS/CdS core/shell QDs can be further synthesized via the cation exchange approach. Our method resulted in high quantum yield, good stability, monodisperse QD solutions with a full surface coverage by excess Cd cations. In addition, we used our core/shell QDs in a photoelectrochemical cell for hydrogen generation. This heterostructure exhibited a saturated photocurrent as high as 3.3 mA cm−2, leading to ~29 ml cm−2 d−1 hydrogen generation, indicating the strong potential of our core/shell QDs for applications in water splitting.
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| 36. |
- Zhao, Haiguang, et al.
(författare)
-
Solar Concentrators : Absorption Enhancement in “Giant” Core/Alloyed-Shell Quantum Dots for Luminescent Solar Concentrator
- 2016
-
Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 12:38
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- On page 5354, H. G. Zhao, F. Rosei, A. Vomiero, and co-workers, demonstrate the application of “giant” core/shell quantum dots as light harvesters in high-performance luminescent solar concentrators (LSCs) with over 1.15% power conversion efficiency. Metal doping approach can tune the absorption spectra of QDs to better match the solar spectrum, and represents a significant advance for the development of high-efficiency LSCs for cost-effective photovoltaic applications.
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| 37. |
- Zhao, Haiguang, et al.
(författare)
-
Tailoring the Heterostructure of Colloidal Quantum Dots for Ratiometric Optical Nanothermometry
- 2020
-
Ingår i: Small. - : John Wiley & Sons. - 1613-6810 .- 1613-6829. ; 16:28
-
Forskningsöversikt (refereegranskat)abstract
- Colloidal quantum dots (QDs) are a fascinating class of semiconducting nanocrystals, thanks to their optical properties tunable through size and composition, and simple synthesis methods. Recently, colloidal double‐emission QDs have been successfully applied as competitive optical temperature sensors, since they exhibit structure‐tunable double emission, temperature‐dependent photoluminescence, high quantum yield, and excellent photostability. Until now, QDs have been used as nanothermometers for in vivo biological thermal imaging, and thermal mapping in complex environments at the sub‐microscale to nanoscale range. In this Review, recent progress for QD‐based nanothermometers is highlighted and perspectives for future work are described.
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| 38. |
- Zhao, Haiguang, et al.
(författare)
-
Tailoring the interfacial structure of colloidal “giant” quantum dots for optoelectronic applications
- 2018
-
Ingår i: Nanoscale. - Cambridge : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 10:36, s. 17189-17197
-
Tidskriftsartikel (refereegranskat)abstract
- Colloidal semiconductor quantum dots (QDs) are promising building blocks for the realization of future optoelectronic technologies, thanks to their size-tunable electronic and optical properties. Among various types of QDs, colloidal “giant” QDs (g-QDs, core/thick-shell) have been widely used in different applications, such as solar cells, light emitting devices, luminescent solar concentrators and photoelectrochemical (PEC) hydrogen production. However, g-QDs have a thick-shell which serves as a physical barrier for electron and hole transfer, leading to a slow charge transfer rate. In this work, we synthesized CdSe/CdSexS1−x/CdS core/shell/shell g-QDs with an intermediate CdSexS1−x alloyed layer. The presence of this interfacial layer largely improves the absorption of CdSe/CdS QDs, particularly in the 300–650 nm range. By engineering the interfacial layer, the holes can leak more into the CdS shell region compared to that of CdSe/CdS QDs. PEC devices based on alloyed g-QDs exhibit a 20% higher saturated photocurrent density (11 ± 0.5 mA cm−2) compared to CdSe/CdS QDs. In addition, after one-hour illumination (100 mW cm−2), the PEC cell based on alloyed g-QDs still exhibits a photocurrent density of 7.5 mA cm−2, maintaining 70% of its initial value. Such alloyed g-QDs are very promising for several emerging optoelectronic applications, where charge separation, transfer and transport play a critical role for the realization of high performance devices.
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| 39. |
- Zhao, Haiguang, et al.
(författare)
-
Temperature Sensors : Ultrasensitive, Biocompatible, Self-Calibrating, Multiparametric Temperature Sensors
- 2015
-
Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 11:43, s. 5740-
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- PbS/CdS core/shell quantum dots are applied as ultrasensitive, biocompatible, self-calibrating, multi-parametric temperature sensors by H. Zhao, A. Vomiero, and F. Rosei. On page 5741, they show how part of the colour emission comes from the PbS core and part from the CdS shell. The relative intensity of these emissions is temperature-dependent, inducing color changes when the temperature varies. The lifetime and peak position of PbS emission also monotonically change with the temperature, offering a platform for a multi-parametric detection system.
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| 40. |
- Zhao, Haiguang, et al.
(författare)
-
Ultrasensitive, Biocompatible, Self-Calibrating, Multiparametric Temperature Sensors
- 2015
-
Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 11:43, s. 5741-5746
-
Tidskriftsartikel (refereegranskat)abstract
- Core–shell quantum dots serve as self-calibrating, ultrasensitive, multiparametric, near-infrared, and biocompatible temperature sensors. They allow temperature measurement with nanometer accuracy in the range 150–373 K, the broadest ever recorded for a nanothermometer, with sensitivities among the highest ever reported, which makes them essentially unique in the panorama of biocompatible nanothermometers with potential for in vivo biological thermal imaging and/or thermoablative therapy.
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| 41. |
- Zhou, Yufeng, et al.
(författare)
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Luminescent Solar Concentrators : Near Infrared, Highly Efficient Luminescent Solar Concentrators
- 2016
-
Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 6:11
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The fabrication of a low reabsorption emission loss, high efficient luminescent solar concentrator (LSC) is demonstrated by embedding near infrared (NIR) core/shell quantum dots (QDs) in a polymer matrix. An engineered Stokes shift in NIR core/shell PbS/CdS QDs is achieved via a cation exchange approach by varying the core size and shell thickness through the refined reaction parameters such as reaction time, temperature, precursor molar ratio, etc. The as-synthesized core/shell QDs with high quantum yield (QY) and excellent chemical/photostability exhibit a large Stokes shift with respect to the bare PbS QDs due to the strong core-to-shell electrons leakage. The large-area planar LSC based on core/shell QDs exhibits the highest value (6.1% with a geometric factor of 10) for optical efficiency compared to the bare NIR QD-based LSCs and other reported NIR QD-based LSCs. The suppression of emission loss and the broad absorption of PbS/CdS QDs offer a promising pathway to integrate LSCs and photovoltaic devices with good spectral matching, indicating that the proposed core/shell QDs are strong candidates for fabricating high efficiency semi-transparent large-area LSCs.
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| 42. |
- Zhou, Yufeng, et al.
(författare)
-
Near Infrared, Highly Efficient Luminescent Solar Concentrators
- 2016
-
Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 6:11
-
Tidskriftsartikel (refereegranskat)abstract
- The fabrication of a low reabsorption emission loss, high efficient luminescent solar concentrator (LSC) is demonstrated by embedding near infrared (NIR) core/shell quantum dots (QDs) in a polymer matrix. An engineered Stokes shift in NIR core/shell PbS/CdS QDs is achieved via a cation exchange approach by varying the core size and shell thickness through the refined reaction parameters such as reaction time, temperature, precursor molar ratio, etc. The as-synthesized core/shell QDs with high quantum yield (QY) and excellent chemical/photostability exhibit a large Stokes shift with respect to the bare PbS QDs due to the strong core-to-shell electrons leakage. The large-area planar LSC based on core/shell QDs exhibits the highest value (6.1% with a geometric factor of 10) for optical efficiency compared to the bare NIR QD-based LSCs and other reported NIR QD-based LSCs. The suppression of emission loss and the broad absorption of PbS/CdS QDs offer a promising pathway to integrate LSCs and photovoltaic devices with good spectral matching, indicating that the proposed core/shell QDs are strong candidates for fabricating high efficiency semi-transparent large-area LSCs.
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| 43. |
- Zhou, Yufeng, et al.
(författare)
-
Ultrasmall Nanoplatelets: The Ultimate Tuning of Optoelectronic Properties
- 2017
-
Ingår i: Advanced Energy Materials. - : John Wiley & Sons. - 1614-6832 .- 1614-6840. ; 7:17
-
Tidskriftsartikel (refereegranskat)abstract
- 2D semiconducting nanoplatelets (NPLs) are an emerging class of photoactive materials. They can be used as building blocks in optoelectronic devices thanks to their large absorption coefficient, high carrier mobility, and unique thickness-dependent optical transitions. The main drawback of NPLs is their large lateral size, which results in unfavorable band energy levels and low quantum yield (QY). Here, ultrasmall lead chalcogenide PbSe1- xSx NPLs are prepared, which exhibit an unprecedented QY of ≈60%, the highest ever reported for this structure. The NPLs are applied as light absorber in a photoelectrochemical system, leading to a saturated photocurrent density of ≈5.0 mA cm-2 (44 mL cm-2 d-1), which is a record for NPL-based photoelectrodes in solar-driven hydrogen generation. Ultrasmall NPLs hold the potential for breakthrough developments in the field of optically active nanomaterials.
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