Improvement of Deformation Stability of Al₂O₃ Moisture-Barrier Layer by Insertion of 4-Bipyridine Organic Monolayers

Flexible organic light-emitting diode (OLED) displays are protected from external moisture using an organic–inorganic thin film encapsulation (TFE) structure. The inorganic thin films used in TFE are excellent moisture barriers, but because they are fragile, thick organic thin films must be used together. In this study, 4,4′-bipyridine (4-BP), a small organic molecule, was inserted into the Al₂O₃ inorganic thin film as monomolecular layers to improve the moisture barrier and flexibility properties of the Al₂O₃. The 30-nm-thick Al₂O₃ layer without the 4-BP monomolecular layers cracked after 1000 repeated bendings at a bending radius of 1 mm, but when these organic molecular layers were introduced, cracking occurred delayed to a radius of 0.7 mm. The effect of improving flexibility due to the introduction of these 4-BP monomolecular layers was verified through optical Ca tests before and after repeated bending and rolling. In this way, it was shown that small organic molecules such as 4-BP can be effectively used to improve the moisture barrier and flexibility properties of TFE for flexible OLED displays.