ORCID Profile
0000-0003-4261-0766
Current Organisation
University of Cambridge
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Optical Properties of Materials | Nanotechnology | Molecular and Organic Electronics | Organic Semiconductors
Expanding Knowledge in the Chemical Sciences | Expanding Knowledge in the Physical Sciences |
Publisher: American Chemical Society (ACS)
Date: 24-12-2018
DOI: 10.1021/JACS.7B06274
Abstract: Singlet fission is the spin-allowed conversion of a photogenerated singlet exciton into two triplet excitons in organic semiconductors, which could enable single-junction photovoltaic cells to break the Shockley-Queisser limit. The conversion of singlets to free triplets is mediated by an intermediate correlated triplet pair (TT) state, but an understanding of how the formation and dissociation of these states depend on energetics and morphology is lacking. In this study, we probe the dynamics of TT states in a model endothermic fission system, TIPS-Tc nanoparticles, which show a mixture of crystalline and disordered regions. We observe the formation of different TT states, with varying yield and different rates of singlet decay, depending on the excitation energy. An emissive TT state is observed to grow in over 1 ns when excited at 480 nm, in contrast to excitation at lower energies where this emissive TT state is not observed. This suggests that the pathway for singlet fission in these nanoparticles is strongly influenced by the initial sub-100 fs relaxation of the photoexcited state away from the Franck-Condon point, with multiple possible TT states. On nanosecond time scales, the TT states are converted to free triplets, which suggests that TT states might diffuse into the disordered regions of the nanoparticles where their breakup to free triplets is favored. The free triplets then decay on μs time scales, despite the confined nature of the system. Our results provide important insights into the mechanism of endothermic singlet fission and the design of nanostructures to harness singlet fission.
Publisher: Springer Science and Business Media LLC
Date: 07-03-2022
Publisher: American Chemical Society (ACS)
Date: 10-07-2020
Publisher: American Chemical Society (ACS)
Date: 29-01-2021
Publisher: Springer Science and Business Media LLC
Date: 22-11-2021
Publisher: American Chemical Society (ACS)
Date: 22-09-2023
DOI: 10.1021/JACS.3C05974
Publisher: American Chemical Society (ACS)
Date: 24-01-2019
Publisher: American Chemical Society (ACS)
Date: 05-03-2018
DOI: 10.1021/ACS.JPCLETT.8B00099
Abstract: Singlet exciton fission allows for the generation of two triplet excitons for each photon absorbed within an organic semiconductor. Efficient harvesting of these triplets could allow for the Shockley-Queisser limit on the power conversion efficiency of single-junction photovoltaics to be broken. Here, we show that singlet fission molecules bound directly to PbS quantum dots as ligands can undergo singlet fission with near unity efficiency and can transfer triplets sequentially into the PbS with near unity efficiency. Within the PbS, the excitations recombine, giving rise of the emission of photons. This allows for the doubling of the quantum dot photoluminescence quantum efficiency when photons are absorbed by the singlet fission ligand, as compared to when directly absorbed in the quantum dot. Our approach demonstrates that it is possible to convert the exciton multiplication process of singlet fission into a photon multiplication process and provides a new path to harness singlet fission with photovoltaics.
Publisher: Springer Science and Business Media LLC
Date: 22-03-2023
Publisher: Springer Science and Business Media LLC
Date: 18-10-2021
DOI: 10.1038/S41467-021-26340-6
Abstract: There is a growing interest in obtaining high quality monolayer transition metal disulfides for optoelectronic applications. Surface treatments using a range of chemicals have proven effective to improve the photoluminescence yield of these materials. However, the underlying mechanism for the photoluminescence enhancement is not clear, which prevents a rational design of passivation strategies. Here, a simple and effective approach to significantly enhance the photoluminescence is demonstrated by using a family of cation donors, which we show to be much more effective than commonly used p-dopants. We develop a detailed mechanistic picture for the action of these cation donors and demonstrate that one of them, bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI), enhances the photoluminescence of both MoS 2 and WS 2 to a level double that of the currently best performing super-acid trifluoromethanesulfonimide (H-TFSI) treatment. In addition, the ionic salts used in our treatments are compatible with greener solvents and are easier to handle than super-acids, providing the possibility of performing treatments during device fabrication. This work sets up rational selection rules for ionic chemicals to passivate transition metal disulfides and increases their potential in practical optoelectronic applications.
Publisher: American Chemical Society (ACS)
Date: 17-09-2018
Publisher: American Association for the Advancement of Science (AAAS)
Date: 25-05-2018
Abstract: Organic semiconductors typically exhibit exciton diffusion lengths on the order of tens of nanometers. Jin et al. prepared nanofibers from block polymers consisting of emissive polyfluorene cores surrounded by coronas of polyethylene glycol and polythiophene (see the Perspective by Holmes). Excitons generated in the polyfluorene cannot enter the polyethylene glycol layer and so diffuse more than 200 nm. This distance can be tuned by varying the length of the polyethylene glycol—a feature that could potentially be exploited in the development of organic devices such as photovoltaics. Science , this issue p. 897 see also p. 854
Publisher: American Chemical Society (ACS)
Date: 27-06-2022
DOI: 10.1021/JACS.2C02631
Publisher: American Chemical Society (ACS)
Date: 14-06-2021
Publisher: American Chemical Society (ACS)
Date: 12-10-2020
Publisher: Springer Science and Business Media LLC
Date: 12-06-2023
Publisher: American Chemical Society (ACS)
Date: 25-10-2019
DOI: 10.1021/JACS.9B10981
Publisher: American Chemical Society (ACS)
Date: 23-07-2019
DOI: 10.1021/JACS.9B06584
Publisher: American Chemical Society (ACS)
Date: 13-05-2021
Publisher: American Chemical Society (ACS)
Date: 06-09-2019
Abstract: Heterostructured two-dimensional colloidal nanoplatelets are a class of material that has attracted great interest for optoelectronic applications due to their high photoluminescence yield, atomically tunable thickness, and ultralow lasing thresholds. Of particular interest are laterally heterostructured core-crown nanoplatelets with a type-II band alignment, where the in-plane spatial separation of carriers leads to indirect (or charge transfer) excitons with long lifetimes and bright, highly Stokes shifted emission. Despite this, little is known about the nature of the lowest energy exciton states responsible for emission in these materials. Here, using polarization-controlled, steady-state, and time-resolved photoluminescence measurements, at temperatures down to 1.6 K and magnetic fields up to 30 T, we study the exciton fine structure and spin dynamics of archetypal type-II CdSe/CdTe core-crown nanoplatelets. Complemented by theoretical modeling and zero-field quantum beat measurements, we find the bright-exciton fine structure consists of two linearly polarized states with a fine structure splitting ∼50 μeV and an indirect exciton Landé
Publisher: American Chemical Society (ACS)
Date: 16-08-1970
Publisher: Springer Science and Business Media LLC
Date: 24-08-2022
DOI: 10.1038/S41467-022-32669-3
Abstract: I-V-VI 2 ternary chalcogenides are gaining attention as earth-abundant, nontoxic, and air-stable absorbers for photovoltaic applications. However, the semiconductors explored thus far have slowly-rising absorption onsets, and their charge-carrier transport is not well understood yet. Herein, we investigate cation-disordered NaBiS 2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching 5 cm −1 just above its pseudo-direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast (picosecond-time scale) photoconductivity decay and long-lived charge-carrier population persisting for over one microsecond in NaBiS 2 nanocrystals. These unusual features arise because of the localised, non-bonding S p character of the upper valence band, which leads to a high density of electronic states at the band edges, ultrafast localisation of spatially-separated electrons and holes, as well as the slow decay of trapped holes. This work reveals the critical role of cation disorder in these systems on both absorption characteristics and charge-carrier kinetics.
Publisher: American Chemical Society (ACS)
Date: 16-08-2021
Publisher: American Chemical Society (ACS)
Date: 20-10-2020
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2016
End Date: 2017
Amount: $360,000.00
Funder: Australian Research Council
View Funded Activity