Here, films using CdSe nanocrystal (NC) triplet photosensitizers in conjunction with diphenylanthracene (DPA) emitters were assembled to address several challenges to practical applications for solution-based photon upconversion. By using poly(9-vinylcarbazole) as a phosphorescent host in this film, volatile organic solvents are eliminated, the spontaneous crystallization of the emitter is significantly retarded, and ∼1.5% photon upconversion quantum yield (out of a maximum of 50%) is obtained. Transient absorption spectroscopy on nanosecond-to-microsecond time scales reveals this efficiency is enabled by an exceptionally long triplet lifetime of 3.4 ± 0.3 ms. Ultimately, we find the upconversion efficiency is limited by incomplete triplet–triplet annihilation, which occurs with a rate 3–4 orders of magnitude slower than in solution-phase upconversion systems.
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Noncrystallizable Charge‐Transporting Hosts for Phosphorescent Organic Light Emitting Diodes: Decreased Emitter Aggregation
Organic light emitting diodes (OLEDs) with phosphorescent emitters (PhOLEDs) exhibit efficiency roll‐off at high luminance because the long‐lived triplet excitons are prone to emission quenching and triplet–triplet annihilation (TTA). Herein, the synthesis, purification, and characterization of an emitter layer host that is a noncrystallizable mixture of isomers (OLEDIQ HT‐1700) is described. In this host, the triplet lifetime of a phosphorescent yellow emitter (IYD‐560) is increased relative to a conventional single‐molecule host (3,3′‐di(9H‐carbazol‐9‐yl)‐1,1′‐biphenyl, mCBP), with high photoluminescence quantum yields and unchanged emission spectra. Characterization of the doped films with differential scanning calorimetry (DSC) and microscopy showed that the emitter is incompatible in mCBP but totally compatible with the noncrystalline host. The increased triplet lifetime is interpreted as decreased triplet quenching in the noncrystallizable host‐based film, while emitter aggregation in the conventional host film leads to triplet quenching.
- NSF-PAR ID:
- 10132704
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- physica status solidi (RRL) – Rapid Research Letters
- Volume:
- 14
- Issue:
- 4
- ISSN:
- 1862-6254
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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