| 1. |
- Toolan, Daniel T. W., et al.
(author)
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Insights into the Structure and Self-Assembly of Organic-Semiconductor/Quantum-Dot Blends
- 2022
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In: Advanced Functional Materials. - : John Wiley & Sons. - 1616-301X .- 1616-3028. ; 32:13
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Journal article (peer-reviewed)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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| 2. |
- Cappel, Ute B, et al.
(author)
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Charge Generation Dynamics in CdS : P3HT Blends for Hybrid Solar Cells.
- 2013
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:24, s. 4253-7
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Journal article (peer-reviewed)abstract
- Development of design rules for hybrid inorganic-organic solar cells through understanding charge generation and recombination dynamics is an important pathway for the improvement of solar cell conversion efficiencies. In this Letter, we study the dynamics of charge generation in CdS:polymer blends by transient absorption spectroscopy. We show that charge generation following excitation of the inorganic component is highly efficient and can occur up to a few nanoseconds after excitation, allowing for diffusion of charges within the inorganic component to an interface. In contrast, charge generation following excitation of the organic component occurs on subpicosecond time scales but suffers from two loss processes, incomplete exciton dissociation and geminate recombination.
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| 3. |
- Dowland, Simon A., et al.
(author)
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Photoinduced electron and hole transfer in CdS:P3HT nanocomposite films : effect of nanomorphology on charge separation yield and solar cell performance
- 2013
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In: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 1:44, s. 13896-13901
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Journal article (peer-reviewed)abstract
- The influence of morphology on the photophysical properties of blend films containing in situ grown CdS and poly(3-hexylthiophene-2,5-diyl) (P3HT), fabricated utilising a metal xanthate single source precursor, is reported. A combination of transient absorption spectroscopy (TAS), transmission electron microscopy (TEM) and photovoltaic device measurements are employed to study the relationship between the efficiency of charge separation, photocurrent generation and thin film morphology. We identify that a significant proportion of the extractable charge originates from the direct excitation of CdS followed by hole-transfer to the P3HT polymer. The yield of this hole-transfer step from the inorganic CdS to the organic polymer is largely unaffected by the film’s nanomorphology, while the dissociation of P3HT excitons into free charges at the CdS:P3HT interface is found to be strongly dependent on this parameter with high yields of charge transfer only being achieved at high CdS loadings. The present study elucidates design rules for the optimization of hybrid inorganic-organic solar energy conversion devices.
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| 4. |
- MacLachlan, Andrew J, et al.
(author)
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Polymer/Nanocrystal Hybrid Solar Cells : Influence of Molecular Precursor Design on Film Nanomorphology, Charge Generation and Device Performance.
- 2015
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In: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 25:3, s. 409-420
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Journal article (peer-reviewed)abstract
- In this work, molecular tuning of metal xanthate precursors is shown to have a marked effect on the heterojunction morphology of hybrid poly(3-hexylthiophene-2,5-diyl) (P3HT)/CdS blends and, as a result, the photochemical processes and overall performance of in situ fabricated hybrid solar cells. A series of cadmium xanthate complexes is synthesized for use as in situ precursors to cadmium sulfide nanoparticles in hybrid P3HT/CdS solar cells. The formation of CdS domains is studied by simultaneous GIWAXS (grazing incidence wide-angle X-ray scattering) and GISAXS (grazing incidence small-angle X-ray scattering), revealing knowledge about crystal growth and the formation of different morphologies observed using TEM (transmission electron microscopy). These measurements show that there is a strong relationship between precursor structure and heterojunction nanomorphology. A combination of TAS (transient absorption spectroscopy) and photovoltaic device performance measurements is used to show the intricate balance required between charge photogeneration and percolated domains in order to effectively extract charges to maximize device power conversion efficiencies. This study presents a strong case for xanthate complexes as a useful route to designing optimal heterojunction morphologies for use in the emerging field of hybrid organic/inorganic solar cells, due to the fact that the nanomorphology can be tuned via careful design of these precursor materials.
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| 5. |
- Gorman, Jeffrey, et al.
(author)
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Deoxyribonucleic Acid Encoded and Size-Defined π-Stacking of Perylene Diimides
- 2022
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:1, s. 368-376
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Journal article (peer-reviewed)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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| 6. |
- Gray, Victor, Dr, 1988-, et al.
(author)
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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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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 146:11, s. 7763-7770
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Journal article (peer-reviewed)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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| 7. |
- Toolan, Daniel T. W., et al.
(author)
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Linking microscale morphologies to localised performance in singlet fission quantum dot photon multiplier thin films
- 2022
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In: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 10:31, s. 11192-11198
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Journal article (peer-reviewed)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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| 8. |
- Weir, Michael P., et al.
(author)
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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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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 10:16, s. 4713-4719
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Journal article (peer-reviewed)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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