Effect of molecular structure of host materials on thermal stability and device characteristics of solution processed oleds

초록

The light emitting layer of organic light emitting diode (OLED) is formed by uniformly mixing host and dopant. However, phase separation is often observed during fabrication of solution processed OLEDs. In particular, phase separation due to stacking is frequently observed during thermal annealing. Hence, the materials with a high glass transition temperature (Tg) are required because phase separation accelerates during annealing process if Tg is too low. To understand this phenomenon, we synthesized two host materials with similar molecular weights but different three-dimensional connectivity which causes different rotational freedom. In both cases, when the annealing temperature rises above 120 °C, the dopant completely escaped from the EML. However, the material that does not disturb the molecular stacking order by annealing due to its limited free rotation through internal bond shows much better device characteristics even after annealing at a higher temperature than Tg. © 2020 SID.

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