| 1. |
- Carrod, Andrew J., 1994, et al.
(författare)
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Recent advances in triplet-triplet annihilation upconversion and singlet fission, towards solar energy applications
- 2022
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 15, s. 4982-5016
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Forskningsöversikt (refereegranskat)abstract
- Solar energy is an ample renewable energy resource, with photovoltaic (PV) technology enabling a direct route from light to electricity. Currently, PVs are limited in photon conversion efficiency, due in major part to spectral losses. Mitigation of these losses is therefore important, economically and environmentally. Two processes that aim to increase solar light utilisation are described herein. The first is triplet-triplet annihilation upconversion (TTA-UC), through which two incoherent photons of low energy can produce one of higher energy, reducing below bandgap losses. Secondly, singlet fission (SF), through which two triplet states may be obtained from one initial singlet excited state, in theory allowing two electrons per photon in a PV, reducing thermalisation losses. These fields are often covered seperately, despite being the reverse processes of one another. This work aims to consolidate research in the two fields and highlight their similarities and common challenges, specifically those relevant to PV applications. Herein, we cover systems primarily based on organic small molecules (anthracene, rubrene, tetracene, pentacene), and detail the fabrication of functional materials containing them (MOFs, gels, SAMs on TiO2, thin evaporated and solution cast films, and cavities). We further offer our recommendations for the focus of future work in both the TTA and SF fields, and discuss the need to address current limitations such as poor triplet diffusion, limited charge injection to PVs, and material stability. Specifically, one could do this by cherry picking ideas from other research fields, for example photosensitisers for photodynamic therapy could be used as TTA sensitisers, and molecules having a considerable excited state aromaticity could be considered as SF materials. We hope this review may aid development towards the end goal of an efficient PV, incorporating either, or both, SF and TTA-UC materials.
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| 2. |
- Congrave, Daniel G., et al.
(författare)
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Suppressing aggregation induced quenching in anthracene based conjugated polymers
- 2021
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Ingår i: Polymer Chemistry. - : Royal Society of Chemistry. - 1759-9954 .- 1759-9962. ; 12:12, s. 1830-1836
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Tidskriftsartikel (refereegranskat)abstract
- Anthracene is a highly valuable building block for luminescent conjugated polymers, particularly when a large singlet-triplet energy gap (Delta E-ST) is desired. Unfortunately, the extended pi system of anthracene imparts a strong tendency for polymer aggregation, resulting in detrimental effects on its solid state photophysics. A large decrease in photoluminescence quantum yield (PLQY, phi(F)) on going from solution to the solid state is especially common, represented in terms of a low phi(R) (phi(R) = phi(F film)/phi(F sol.)). Significant and undesirable red-shifting of fluorescence in the solid state is also typical due to processes such as excimer formation. In this work a series of alkylene-encapsulated conjugated anthracene polymers is developed to overcome these challenging problems. We demonstrate a promising material which displays a good solid state PLQY that is effectively unchanged compared to solution measurements (phi(R) similar to 1, phi(F film) similar to 40%), alongside an identical PL 0-0 transition wavelength in solution and thin film. Such a direct transfer of luminescence properties from solution to the solid state is remarkable for a conjugated polymer and completely unprecedented for one based on anthracene.
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| 3. |
- Gorman, Jeffrey, et al.
(författare)
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Deoxyribonucleic Acid Encoded and Size-Defined π-Stacking of Perylene Diimides
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:1, s. 368-376
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Tidskriftsartikel (refereegranskat)abstract
- Natural photosystems use protein scaffolds to control intermolecular interactions that enable exciton flow, charge generation, and long-range charge separation. In contrast, there is limited structural control in current organic electronic devices such as OLEDs and solar cells. We report here the DNA-encoded assembly of pi-conjugated perylene diimides (PDIs) with deterministic control over the number of electronically coupled molecules. The PDIs are integrated within DNA chains using phosphoramidite coupling chemistry, allowing selection of the DNA sequence to either side, and specification of intermolecular DNA hybridization. In this way, we have developed a "toolbox" for construction of any stacking sequence of these semiconducting molecules. We have discovered that we need to use a full hierarchy of interactions: DNA guides the semiconductors into specified close proximity, hydrophobic-hydrophilic differentiation drives aggregation of the semiconductor moieties, and local geometry and electrostatic interactions define intermolecular positioning. As a result, the PDIs pack to give substantial intermolecular pi wave function overlap, leading to an evolution of singlet excited states from localized excitons in the PDI monomer to excimers with wave functions delocalized over all five PDIs in the pentamer. This is accompanied by a change in the dominant triplet forming mechanism from localized spin-orbit charge transfer mediated intersystem crossing for the monomer toward a delocalized excimer process for the pentamer. Our modular DNA-based assembly reveals real opportunities for the rapid development of bespoke semiconductor architectures with molecule-by-molecule precision.
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| 4. |
- Gray, Victor, Dr, 1988-, et al.
(författare)
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Direct vs Delayed Triplet Energy Transfer from Organic Semiconductors to Quantum Dots and Implications for Luminescent Harvesting of Triplet Excitons
- 2020
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Ingår i: ACS Nano. - : AMER CHEMICAL SOC. - 1936-0851 .- 1936-086X. ; 14:4, s. 4224-4234
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid inorganic-organic materials such as quantum dots (QDs) coupled with organic semiconductors have a wide range of optoelectronic applications, taking advantage of the respective materials' strengths. A key area of investigation in such systems is the transfer of triplet exciton states to and from QDs, which has potential applications in the luminescent harvesting of triplet excitons generated by singlet fission, in photocatalysis and photochemical upconversion. While the transfer of energy from QDs to the triplet state of organic semiconductors has been intensely studied in recent years, the mechanism and materials parameters controlling the reverse process, triplet transfer to QDs, have not been well investigated. Here, through a combination of steady-state and time-resolved optical spectroscopy we study the mechanism and energetic dependence of triplet energy transfer from an organic ligand (TIPS-tetracene carboxylic acid) to PbS QDs. Over an energetic range spanning from exothermic (-0.3 eV) to endothermic (+0.1 eV) triplet energy transfer we find that the triplet energy transfer to the QD occurs through a single step process with a clear energy dependence that is consistent with an electron exchange mechanism as described by Marcus-Hush theory. In contrast, the reverse process, energy transfer from the QD to the triplet state of the ligand, does not show any energy dependence in the studied energy range; interestingly, a delayed formation of the triplet state occurs relative to the quantum dots' decay. Based on the energetic dependence of triplet energy transfer we also suggest design criteria for future materials systems where triplet excitons from organic semiconductors are harvested via QDs, for instance in light emitting structures or the harvesting of triplet excitons generated via singlet fission.
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| 5. |
- Gray, Victor, Dr, 1988-, et al.
(författare)
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Ligand-Directed Self-Assembly of Organic-Semiconductor/Quantum-Dot Blend Films Enables Efficient Triplet Exciton-Photon Conversion
- 2024
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 146:11, s. 7763-7770
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Tidskriftsartikel (refereegranskat)abstract
- Blends comprising organic semiconductors and inorganic quantum dots (QDs) are relevant for many optoelectronic applications and devices. However, the individual components in organic-QD blends have a strong tendency to aggregate and phase-separate during film processing, compromising both their structural and electronic properties. Here, we demonstrate a QD surface engineering approach using electronically active, highly soluble semiconductor ligands that are matched to the organic semiconductor host material to achieve well-dispersed inorganic-organic blend films, as characterized by X-ray and neutron scattering, and electron microscopies. This approach preserves the electronic properties of the organic and QD phases and also creates an optimized interface between them. We exemplify this in two emerging applications, singlet-fission-based photon multiplication (SF-PM) and triplet-triplet annihilation-based photon upconversion (TTA-UC). Steady-state and time-resolved optical spectroscopy shows that triplet excitons can be transferred with near unity efficiently across the organic-inorganic interface, while the organic films maintain efficient SF (190% yield) in the organic phase. By changing the relative energy between organic and inorganic components, yellow upconverted emission is observed upon 790 nm NIR excitation. Overall, we provide a highly versatile approach to overcome longstanding challenges in the blending of organic semiconductors with QDs that have relevance for many optical and optoelectronic applications.
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| 6. |
- Gray, Victor, Dr, 1988-, et al.
(författare)
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Organic-quantum dot hybrid interfaces and their role in photon fission/fusion applications
- 2021
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Ingår i: Chemical Physics Reviews. - : American Institute of Physics (AIP). - 2688-4070. ; 2:3
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Forskningsöversikt (refereegranskat)abstract
- Solar energy is rapidly becoming a more important aspect in today's energy systems, and solar cells are playing a major role in this shift. However, to further boost the efficiency of conventional solar cells, fundamental thermodynamic limits must be overcome. Photon fission and photon fusion, also known as photon downconversion and photon upconversion, are gaining increasing attention as a means to improve solar energy harvesting in solar cells by overcoming thermalization and transmission losses, respectively. Important developments in these fields include the use of organic-inorganic hybrid materials that can leverage the advantages of each material. In this review, we look at the development of organic-quantum dot (QD) hybrid materials and their use as components of photon fission and fusion systems. We put a particular focus on the triplet energy transfer across these organic-inorganic hybrid interfaces and how this understanding has been developed. In the later part of the review, we focus on the recent examples of these hybrid materials as crucial components in solar energy harvesting applications based on triplet-triplet annihilation photon upconversion or singlet-fission-based photon multiplication. By highlighting the most relevant discoveries toward understanding and designing organic-QD hybrid interfaces for photon fission and fusion applications, we establish a starting point for researchers to continue moving this research field forward toward practical applications.
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| 7. |
- Gray, Victor, Dr, 1988-, et al.
(författare)
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Thiol-Anchored TIPS-Tetracene Ligands with Quantitative Triplet Energy Transfer to PbS Quantum Dots and Improved Thermal Stability
- 2020
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Ingår i: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 11:17, s. 7239-7244
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Tidskriftsartikel (refereegranskat)abstract
- Triplet energy transfer between inorganic quantum dots (QDs) and organic materials plays a fundamental role in many optoelectronic applications based on these nanocomposites. Attaching organic molecules to the QD as transmitter ligands has been shown to facilitate transfer both to and from QDs. Here we show that the often disregarded thiol anchoring group can achieve quantitative triplet energy transfer yields in a PbS QD system with 6,11-bis[(triisopropylsilyl)ethynyl]tetracene-2-methylthiol (TET-SH) ligands. We demonstrate efficient triplet transfer in a singlet fission-based photon multiplication system with 5,12-bis[(triisopropylsilyl)ethynyl]tetracene generating triplets in solution that transfer to the PbS QDs via the thiol ligand TET-SH. Importantly, we demonstrate the increased thermal stability of the PbS/TET-SH system, compared to the traditional carboxylic acid counterpart, allowing for higher photoluminescence quantum yields.
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| 8. |
- Gray, Victor, Dr, 1988-, et al.
(författare)
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Triplet transfer from PbS quantum dots to tetracene ligands : is faster always better?
- 2022
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 10:43, s. 16321-16329
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Tidskriftsartikel (refereegranskat)abstract
- Quantum dot-organic semiconductor hybrid materials are gaining increasing attention as spin mixers for applications ranging from solar harvesting to spin memories. Triplet energy transfer between the inorganic quantum dot (QD) and organic semiconductor is a key step to understand in order to develop these applications. Here we report on the triplet energy transfer from PbS QDs to four energetically and structurally similar tetracene ligands. Even with similar ligands we find that the triplet energy transfer dynamics can vary significantly. For TIPS-tetracene derivatives with carboxylic acid, acetic acid and methanethiol anchoring groups on the short pro-cata side we find that triplet transfer occurs through a stepwise process, mediated via a surface state, whereas for monosubstituted TIPS-tetracene derivative 5-(4-benzoic acid)-12-triisopropylsilylethynyl tetracene (BAT) triplet transfer occurs directly, albeit slower, via a Dexter exchange mechanism. Even though triplet transfer is slower with BAT the overall yield is greater, as determined from upconverted emission using rubrene emitters. This work highlights that the surface-mediated transfer mechanism is plagued with parasitic loss pathways and that materials with direct Dexter-like triplet transfer are preferred for high-efficiency applications.
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| 9. |
- Nishimura, Naoyuki, et al.
(författare)
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Photon Upconversion from Near-Infrared to Blue Light with TIPS-Anthracene as an Efficient Triplet-Triplet Annihilator
- 2019
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Ingår i: ACS Materials Letters. - : AMER CHEMICAL SOC. - 2639-4979. ; 1:6, s. 660-664
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Tidskriftsartikel (refereegranskat)abstract
- Photon upconversion (PUC) via triplet-triplet annihilation (TTA) from near-infrared (NIR) to blue photons could have important applications especially to bioimaging and drug delivery accompanied by photochemical reaction. The fundamental challenges in achieving this has been the large anti-Stokes shift combined with the need to efficiently sensitize within the biological transparency window (700-900 nm). This calls for materials combinations with minimal energy losses during sensitization and minimal energy requirements to drive efficient TTA. Here, we demonstrate efficient PUC converting from NIR energy to blue photons using the commercially available material 9,10-bis[((triisopropyl)silyl)ethynyl]anthracene (TIPS-Ac) as the annihilator. With a conventional triplet sensitizing system, TIPS-Ac performed TTA with an efficiency of 77 +/- 3% despite a relatively small driving force, compared to conventional TTA material converting from NIR to blue, for the TTA of less than 0.32 eV. Combined with Pt(II) meso-tetraphenyltetrabenzoporphine (PtTPBP), which is a heavy atom triplet sensitizer that directly generates triplets upon NIR photon excitation, the resulting system allowed for an anti-Stokes shift of 1.03 eV. Our results highlight the use of direct triplet generation via NIR excitation as a useful path to achieving large anti-Stokes shift and also show that high TTA efficiencies can be achieved even in the absence of large driving energies for the TTA process.
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| 10. |
- Toolan, Daniel T. W., et al.
(författare)
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Insights into the Structure and Self-Assembly of Organic-Semiconductor/Quantum-Dot Blends
- 2022
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Ingår i: Advanced Functional Materials. - : John Wiley & Sons. - 1616-301X .- 1616-3028. ; 32:13
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Tidskriftsartikel (refereegranskat)abstract
- Controlling the dispersibility of crystalline inorganic quantum dots (QD) within organic-QD nanocomposite films is critical for a wide range of optoelectronic devices. A promising way to control nanoscale structure in these nanocomposites is via the use of appropriate organic ligands on the QD, which help to compatibilize them with the organic host, both electronically and structurally. Here, using combined small-angle X-ray and neutron scattering, the authors demonstrate and quantify the incorporation of such a compatibilizing, electronically active, organic semiconductor ligand species into the native oleic acid ligand envelope of lead sulphide, QDs, and how this ligand loading may be easily controlled. Further more, in situ grazing incidence wide/small angle X-ray scattering demonstrate how QD ligand surface chemistry has a pronounced effect on the self-assembly of the nanocomposite film in terms of both small-molecule crystallization and QD dispersion versus ordering/aggregation. The approach demonstrated here shows the important role which the degree of incorporation of an active ligand, closely related in chemical structure to the host small-molecule organic matrix, plays in both the self-assembly of the QD and small-molecule components and in determining the final optoelectronic properties of the system.
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| 11. |
- Toolan, Daniel T. W., et al.
(författare)
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Linking microscale morphologies to localised performance in singlet fission quantum dot photon multiplier thin films
- 2022
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 10:31, s. 11192-11198
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid small-molecule/quantum dot films have the potential to reduce thermalization losses in single-junction photovoltaics as photon multiplication devices. Here grazing incidence X-ray scattering, optical microscopy and IR fluorescence microscopy (probing materials at two distinct wavelengths), provide new insight into highly complex morphologies across nm and mu m lengthscales to provide direct links between morphologies and photon multiplication performance. Results show that within the small molecule crystallites three different QD morphologies may be identified; (i) large quantum dot aggregates at the crystallite nucleus, (ii) relatively well-dispersed quantum dots and (iii) as aggregated quantum dots "swept" from the growing crystallite and that regions containing aggregate quantum dot features lead to relatively poor photon multiplication performance. These results establish how combinations of scattering and microscopy may be employed to reveal new insights into the structure and function of small molecule:quantum dot blends.
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| 12. |
- Weir, Michael P., et al.
(författare)
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Ligand Shell Structure in Lead Sulfide–Oleic Acid Colloidal Quantum Dots Revealed by Small-Angle Scattering
- 2019
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 10:16, s. 4713-4719
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystal quantum dots are generally coated with an organic ligand layer. These layers are a necessary consequence of their chemical synthesis, and in addition they play a key role in controlling the optical and electronic properties of the system. Here we describe a method for quantitative measurement of the ligand layer in 3 nm diameter lead sulfide–oleic acid quantum dots. Complementary small-angle X-ray and neutron scattering (SAXS and SANS) studies give a complete and quantitative picture of the nanoparticle structure. We find greater-than-monolayer coverage of oleic acid and a significant proportion of ligand remaining in solution, and we demonstrate reversible thermal cycling of the oleic acid coverage. We outline the effectiveness of simple purification procedures with applications in preparing dots for efficient ligand exchange. Our method is transferrable to a wide range of colloidal nanocrystals and ligand chemistries, providing the quantitative means to enable the rational design of ligand-exchange procedures.
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