Optical upconversion (UC) of low energy photons into high energy photons enables solar cells to harvest photons with energies below the band gap of the absorber, reducing the transmission loss. UC based on triplet–triplet annihilation (TTA) in organic chromophores can upconvert photons from sunlight, albeit with low conversion efficiency. We utilize three energy-based criteria to assess the UC potential of TTA emitters in terms of the quantum yield (QY) and the anti-Stokes shift. The energy loss in the singlet pathway of an emitter encounter complex, where a high energy photon is emitted, determines whether a chromophore may undergo TTA. The energy loss in the triplet pathway, which is the main competing process, impacts the TTA QY. The energy difference between the lowest singlet and triplet excitation states in TTA emitters sets an upper bound for the anti-Stokes shift of TTA-UC. Using the energetic criteria evaluated by time-dependent density functional theory (TDDFT) calculations, we find that benzo[ a ]tetracene, benzo[ a ]pyrene, and their derivatives are promising TTA emitters. The energetics assessment and computer simulations could be used to efficiently discover and design more candidate high-performance TTA emitters.
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Extracting accurate information from triplet–triplet annihilation upconversion data with a mass-conserving kinetic model
Triplet–triplet annihilation upconversion (TTA-UC) is a process that shows promise for applications such as energy-harvesting and light-generation technologies. The irradiance dependent performance of TTA-UC systems is typically gauged using a graphical analysis, rather than a detailed model. Additionally, kinetic models for TTA-UC rarely incorporate mass conservation, which is a phenomenon that can have important consequences under experimentally relevant conditions. We present an analytical, mass-conserving kinetic model for TTA-UC, and demonstrate that the mass-conservation constraint cannot generally be ignored. This model accounts for saturation in TTA-UC data. Saturation complicates the interpretation of the threshold irradiance I th , a popular performance metric. We propose two alternative figures of merit for overall performance. Finally, we show that our model can robustly fit experimental data from a wide variety of sensitized TTA-UC systems, enabling the direct and accurate determination of I th and of our proposed performance metrics. We employ this fitting procedure to benchmark and compare these metrics, using data from the literature.
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- NSF-PAR ID:
- 10383086
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 24
- Issue:
- 46
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 28174 to 28190
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The advancement of triplet–triplet annihilation based upconversion (TTA-UC) in emerging technologies necessitates the development of solid-state systems that are readily accessible and broadly applicable. Here, we demonstrate that thiol–ene click chemistry can be used as a facile cure-on-demand synthetic route to access elastomeric films capable of TTA-UC. Photopolymerization of multifunctional thiols in the presence of a thiol-functionalized 9,10-diphenylanthracene (DPA) emitter results in covalent DPA integration and homogenous crosslinked polymer networks. The palladium( ii ) octaethylporphyrin (PdOEP) sensitizer is subsequently introduced into the films through solution immersion. Upon excitation at 544 nm, green-to-blue upconversion is observed with compositional tuning resulting in an optimal upconverted emission intensity at 1.0 wt% DPA and 0.02 wt% PdOEP. The effectiveness of thiol–ene networks to function as robust host materials for solid-state TTA-UC is further demonstrated by improved photostability in air.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2CP03986A
