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The conversion of low energy photons into high energy photons via triplet-triplet annihilation (TTA) photon upconversion (UC) has become a promising avenue for furthering a wide range of optoelectronic applications. Through the decades of research, many combinations of triplet sensitizer species and annihilator molecules have been investigated unlocking the entire visible spectrum upon proper pairings of sensitizer and annihilator identities. Here, we reflect upon the seminal works which lay the foundation for TTA-UC originating from solution-based methods and highlight the recent advances made within the solid state primarily focusing on perovskite-based triplet generation.
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Harnessing near-infrared light via S 0 to T 1 sensitizer excitation in a molecular photon upconversion solar cell
Integrating molecular photon upconversion via triplet–triplet annihilation (TTA-UC) directly into a solar cell offers a means of harnessing sub-bandgap, near infrared (NIR) photons and surpassing the Shockley–Queisser limit. However, all integrated TTA-UC solar cells to date only harness visible light. Here, we incorporate an osmium polypyridal complex (Os) as the triplet sensitizer in a metal ion linked multilayer photoanode that is capable of harnessing NIR light via S 0 to T 1 * excitation, triple energy transfer to a phosphonated bis(9,10-diphenylethynyl)anthracene annihilator (A), TTA-UC, and electron injection into TiO 2 from the upcoverted state. The TiO 2 -A-Zn-Os devices have five-fold higher photocurrent (∼3.5 μA cm −2 ) than the sum of their parts. IPCE data and excitation intensity dependent measurements indicate that the NIR photons are harvested through a TTA-UC mechanism. Transient absorption spectroscopy is used to show that the low photocurrent, as compared to visible light harnessing TTA-UC solar cells, can be atributed to: (1) slow sensitizer to annihilator triplet energy transfer, (2) a low injection yield for the annihilator, and (3) fast back energy transfer from the upconverted state to the sensitizer. Regardless, these results serve as a proof-of-concept that NIR photons can be harnessed via an S 0 to T 1 * sensitizer excited, integrated TTA-UC solar cell and that further improvements can readily be made by remedying the performance limiting processes noted above.
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- PAR ID:
- 10325417
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 10
- Issue:
- 12
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 4947 to 4954
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Triplet‐triplet annihilation upconversion (TTA‐UC) is a photophysical process in which two low‐energy photons are converted into one higher‐energy photon. This type of upconversion requires two species: a sensitizer that absorbs low‐energy light and transfers its energy to an annihilator, which emits higher‐energy light after TTA. In spite of the multitude of applications of TTA‐UC, few families of annihilators have been explored. In this work, we show dipyrrolonaphthyridinediones (DPNDs) can act as annihilators in TTA‐UC. We found that structural changes to DPND dramatically increase its upconversion quantum yield (UCQY). Our optimized DPND annihilator demonstrates a high maximum internal UCQY of 9.4 %, outperforming the UCQY of commonly used near‐infrared‐to‐visible annihilator rubrene by almost double.more » « less
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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.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1TC05270E
