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Engineering Molecular Ligand Shells on Quantum Dots for Quantitative Harvesting of Triplet Excitons Generated by Singlet Fission
Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.ORCID iD: 0000-0001-6003-5991
Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 OHE, England.
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2019 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 32, p. 12907-12915Article in journal (Refereed) Published
Abstract [en]

Singlet fission is an exciton multiplication process in organic molecules in which a photogenerated spin-singlet exciton is rapidly and efficiently converted to two spin-triplet excitons. This process offers a mechanism to break the Shockley-Queisser limit by overcoming the thermalization losses inherent to all single-junction photovoltaics. One of the most promising methods to harness the singlet fission process is via the efficient extraction of the dark triplet excitons into quantum dots (QDs) where they can recombine radiatively, thereby converting high-energy photons to pairs of low-energy photons, which can then be captured in traditional inorganic PVs such as Si. Such a singlet fission photon multiplication (SF-PM) process could increase the efficiency of the best Si cells from 26.7% to 32.5%, breaking the Shockley-Queisser limit. However, there has been no demonstration of such a singlet fission photon multiplication (SF-PM) process in a bulk system to date. Here, we demonstrate a solution-based bulk SF-PM system based on the singlet fission material TIPS-Tc combined with PbS QDs. Using a range of steady-state and time-resolved measurements combined with analytical modeling we study the dynamics and mechanism of the triplet harvesting process. We show that the system absorbs >95% of incident photons within the singlet fission material to form singlet excitons, which then undergo efficient singlet fission in the solution phase (135 +/- 5%) before quantitative harvesting of the triplet excitons (95 +/- 5%) via a low concentration of QD acceptors, followed by the emission of IR photons. We find that in order to achieve efficient triplet harvesting it is critical to engineer the surface of the QD with a triplet transfer ligand and that bimolecular decay of triplets is potentially a major loss pathway which can be controlled via tuning the concentration of QD acceptors. We demonstrate that the photon multiplication efficiency is maintained up to solar fluence. Our results establish the solution-based SF-PM system as a simple and highly tunable platform to understand the dynamics of a triplet energy transfer process between organic semiconductors and QDs, one that can provide clear design rules for new materials.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2019. Vol. 141, no 32, p. 12907-12915
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Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-393736DOI: 10.1021/jacs.9b06584ISI: 000481563500060PubMedID: 31336046OAI: oai:DiVA.org:uu-393736DiVA, id: diva2:1355539
Funder
EU, Horizon 2020, 758826Swedish Research Council, 2018-00238Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2019-09-30Bibliographically approved

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