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LDI-TOF-MS spectra of an aged OLED [(a), (c), (e), (g), (i), and (l)] and a non-IV-driven reference sample [(b), (d), (f), (h), (k), and (m)]. Spectra (a) and (b) show the full spectra of both diodes, where the other spectra show details from them. (c) and (d) prove the presence of BPhen in the samples after the removing of the Al-top contact. (e) shows the proposed reaction products between and BPhen at 648.23 amu as well as the BPhen dimer at 664.3 amu (Ref. 6). (g) indicates that a dimerization of is not detectable at 774 amu as proposed from Ref. 15, (i) shows a reformation of Cs and BPhen to a combined complex at 796.5 amu. Spectrum (l) shows the fragment, a precursor for the complex visible in (e) and/or a degradation product itself.
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Proposed fragmentation (a) of after excitation and further complexation (b) of the fragment with the HBL BPhen by forming a charge transfer complex or a more stable complex with coordinated bonds.
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Metal organic fluorescent and phosphorescent emitters are widely used in organic light emitting devices (OLEDs). Iridium-based triplet emitters are known to undergo chemical reactions with other materials during OLEDaging. The material tris(8-hydroxy-quinolinato)aluminum , which is widely used as electron transporting material and green fluorescent emitter, degrades mainly during hole transport. We investigate the chemical changes in during device aging: using laser desorption ionization time-of-flight mass spectrometry, we study the reaction products found in degraded OLEDs. Similar to the reactions known from the phosphorescent iridium-based emitters, undergoes a dissociation and further reaction with the hole blocking material 4,7-diphenyl-1,10-phenanthroline.
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