Systematic investigation on polymer layer selection for flexible thin film encapsulation

Flexibility of thin film encapsulation (TFE) in implementing flexible organic light emitting diodes is a very important factor. In this work, we mainly focus on improving flexibility by using a proper selection of polymers in the 1.5 dyads (aluminum oxide (Al2O3)/polymer/Al2O3) atomic layer deposition processed TFE structure. As a pre-requisite, we selected four types of polymers (PVP, P2VP, PVB, and P1VN) with different functional groups to compare the flexibility of TFE films. The two factors of polymer, elastic modulus and surface energy, were identified. The lowering of these two factors of polymer show better flexibility. Furthermore, it was confirmed that the interaction between polymer and Al2O3 interaction was not so influenced, but the penetration depth of Al2O3 was important for the flexibility of TFE. This was visually confirmed using transmission electron micro-scopy and energy dispersive spectrometry mapping. With the surface energy lowering, a deeper penetration depth of Al2O3 into the polymer occurred. As a result, the surface stress of Al2O3 was reduced, which deduces the excellent flexibility of TFE.