Engineering Molecular Ligand Shells on Quantum Dots for Quantitative Harvesting of Triplet Excitons Generated by Singlet Fission.

Autor:	Allardice JR; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom., Thampi A; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom., Dowland S; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom., Xiao J; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom., Gray V; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom.; Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, Uppsala SE-751 20 , Sweden., Zhang Z; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom., Budden P; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom., Petty AJ 2nd; Center for Applied Energy Research , University of Kentucky , Research Park Drive , Lexington , Kentucky 40511 , United States., Davis NJLK; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom.; The MacDiarmid Institute for Advanced Materials and Nanotechnology, The Dodd-Walls Centre for Photonic and Quantum Technologies, School of Chemical and Physical Sciences , Victoria University of Wellington , Wellington 6140 , New Zealand., Greenham NC; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom., Anthony JE; Center for Applied Energy Research , University of Kentucky , Research Park Drive , Lexington , Kentucky 40511 , United States., Rao A; Cavendish Laboratory , University of Cambridge , J. J. Thomson Avenue , Cambridge CB3 0HE , United Kingdom.
Jazyk:	angličtina
Zdroj:	Journal of the American Chemical Society [J Am Chem Soc] 2019 Aug 14; Vol. 141 (32), pp. 12907-12915. Date of Electronic Publication: 2019 Aug 02.
DOI:	10.1021/jacs.9b06584
Abstrakt:	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.
Databáze:	MEDLINE
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