| 1. |
- Dembele, Kadiatou Therese, et al.
(författare)
-
Graphene below the percolation threshold in TiO2 for dye-sensitized solar cells
- 2015
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:6, s. 2580-2588
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a fast and large area-scalable methodology for the fabrication of efficient dye sensitized solar cells (DSSCs) by simple addition of graphene micro-platelets to TiO2 nanoparticulate paste (graphene concentration in the range of 0 to 1.5 wt%). Two dimensional (2D) Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirm the presence of graphene after 500°C annealing for 30 minutes. Graphene addition increases the photocurrent density from 12.4 mA cm-2 in bare TiO2 to 17.1 mA cm-2 in an optimized photoanode (0.01 wt% graphene, much lower than those reported in previous studies), boosting the photoconversion efficiency (PCE) from 6.3 up to 8.8%. The investigation of the 2D graphene distribution showed that an optimized concentration is far below the percolation threshold, indicating that the increased PCE does not rely on the formation of an interconnected network, as inferred by prior investigations, but rather, on increased charge injection from TiO2 to the front electrode. These results give insights into the role of graphene in improving the functional properties of DSSCs and identifying a straightforward methodology for the synthesis of new photoanodes.
|
|
| 2. |
- Gilzad Kohan, Mojtaba, et al.
(författare)
-
Plasma assisted vapor solid deposition of Co3O4 tapered nanorods for energy applications
- 2019
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 7:46, s. 26302-26310
-
Tidskriftsartikel (refereegranskat)abstract
- Self-standing, 1-dimensional (1D) structures of p-type metal oxide (MOx) have been the focus of considerable attention, due to their unique properties in energy storage and solar light conversion. However, the practical performance of p-type MOx is intrinsically limited by their interfacial defects and strong charge recombination losses. Single crystalline assembly can significantly reduce recombination at interface and grain boundaries. Here, we present a one-step route based on plasma assisted physical vapor deposition (PVD), for the rational and scalable synthesis of single crystalline 1D vertically aligned Co3O4 tapered nanorods (NRs). The effect of PVD parameters (deposition pressure, temperature and duration) in tuning the morphology, composition and crystalline structure of resultant NRs is investigated. Crystallographic data obtained from X-ray diffraction and high-resolution transmission electron microscopy (TEM) indicated the single crystalline nature of NRs with [111] facet preferred orientation. The NRs present two optical band gaps at about 1.48 eV and 2.1 eV. Current–voltage (I–V) characteristic of the Co3O4 NRs electrodes, 400 nm long, present two times higher current density at −1 V forward bias, compared to the benchmarking thin film counterpart. These array structures exhibit good electrochemical performance in lithium-ion adsorption–desorption processes. Among all, the longest Co3O4 NRs electrodes delivers a 1438.4 F g−1 at current density of 0.5 mA cm−2 and presents 98% capacitance retention after 200 charge–discharge cycles. The very low values of charge transfer resistance (Rct = 5.2 Ω for 400 nm long NRs) of the NRs testifies their high conductivity. Plasma assisted PVD is demonstrated as a facile technique for synthesizing high quality 1D structures of Co3O4, which can be of interest for further development of different desirable 1D systems based on transition MOx.
|
|
| 3. |
- Jin, Lei, et al.
(författare)
-
Dynamics of semiconducting nanocrystal uptake into mesoporous TiO2 thick films by electrophoretic deposition
- 2015
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:2, s. 847-856
-
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).
|
|
| 4. |
- Liu, Cheng, et al.
(författare)
-
Tuning the composition of heavy metal-free quaternary quantum dots for improved photoelectrochemical performance
- 2021
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 9:9, s. 5825-5832
-
Tidskriftsartikel (refereegranskat)abstract
- Colloidal quantum dots (QDs) are promising building blocks towards the development of cost-effective and high-efficiency photoelectrochemical (PEC) cells. Unfortunately, the frequent use of QDs possessing heavy metals (e.g. Cd and Pb) in state-of-the-art QD-based PEC technologies is a major obstacle regarding their future commercial perspective. In this work, we synthesized heavy metal-free quaternary CuZnInS3 (CZIS) with variable Cu : Zn ratios and fabricated corresponding QDs-PEC devices via a facile chemical bath deposition (CBD) technique. It is revealed that the tuned CZIS (1Zn) QDs (i.e. Cu : Zn ratio of 1 : 1) can result in optimized optical properties including enhanced quantum yield, suppressed nonradiative recombination and extended excitonic lifetime. Accordingly, as-fabricated CZIS (1Zn) QD-based photoanodes demonstrated increased charge transfer rate and decreased electron transport resistance for improved PEC performance. The results indicate that tuning the composition of heavy metal-free multinary QDs is one of the promising pathways to achieve eco-friendly and high-performance PEC systems for solar hydrogen production.
|
|
| 5. |
- Liu, Guiju, et al.
(författare)
-
Red-emissive carbon quantum dots enable high efficiency luminescent solar concentrators
- 2023
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 11:16, s. 8950-8960
-
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.
|
|
| 6. |
- 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.
|
|
