Optimizing the gradient stress sandwich structure thin-film encapsulation for super flexible organic light-emitting devices

Abstract

To enable organic light-emitting diodes (OLEDs) to be rolled and folded, we need a flexible encapsulation layer that can protect organic materials and metal electrodes that are susceptible to moisture and oxygen. Thin films that encapsulate organic electronic devices need to have excellent mechanical properties to prevent cracks during bending. Using plasma-enhanced chemical vapor deposition (PECVD) and other techniques, we fabricated high-density, stress gradient sandwich-structured films and studied the residual stress of deposited films on encapsulating films and their effect on delamination and cracking. We found that by adjusting the H2/N2 gas ratio and optimizing the Si:N:H ratio of PECVD SiNx:H films, denser, more etch-resistant, higher compressive stress and lower hydrogen content films can be deposited, thereby enable better flexible thin film encapsulation (TFE). We also deposited an inorganic/organic/inorganic sandwich structure film and utilized stress gradient changes to relieve the tensile stress on the outer film during bending. After standardized testing, the OLED with the stress gradient encapsulation structure has no dark spots after bending 10 000 times (bending radius 2 mm). This technique can be used in flexible TFE for various organic devices, showing promising applications in bendable and wearable products.