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Simulation of light emission from thin-film microcavities

Besides EQE enhancements, the operational lifetime of the devices prepared at ~0.80 to 0.85 Tg is also improved In general, it is a tough and laborious task to investigate the degradation of OLEDs and correlate these findings to the nanoscopic level of the molecular building blocks (42, 59). Here, if only a change of the deposition parameters for EML and ETL (composed mostly of TPBi) leads to a similar correlation with the 0.85 Tg criteria to form an ultrastable glass, that is, LT70 peaks at these deposition temperatures, then it can be deduced that the molecular conformation at the nanoscale favors a more durable device operation. A clear correlation between the glass density and the photostability—which measures the resistance of the material to light irradiation—has been recently established by Qiu et al. (60). They prepare samples of DO37 (3-[[4-(2,6-dichloro-4-nitrophenyl)azo]-N-ethylanilino]-pro-pionitrile or Dispersive Orange 37) glass by physical vapor deposition at different substrate temperatures and find that glasses prepared at 0.88 Tg have, besides higher kinetic stability and higher density, higher photostability. A qualitative argument for the enhanced stability is similar to the one used above for increased radiative efficiency. The rigidity of the films formed as ultrastable glasses is likely to suppress coupling to generally accessible decomposition routes present in OLEDs.