OLED displays are very sensitive to oxygen and water, and better barrier effect is one of the main challenges of the next generation of flexible technology.
The first generation of OLED displays used glass as a barrier layer, but it could not be used in flexible OLEDs because of its poor flexibility. At present, the flexible screen is packaged with thin film, which is composed of SiOx and PI layers alternately. The barrier effect of water and oxygen is acceptable. However, if the flexible display is to be folded or crimpable, it is necessary to find a better OLED packaging technology.
Graphene is the most impermeable material in the world, so the idea of using graphene as water oxygen barrier for OLED has existed for some time. In 2015, a British organization launched a cooperative project called gravia to develop graphene based packaging technology. After two years of research, the project team announced their results.
At ideal purity, no gas can penetrate the graphene layer. Of course, the material in reality is not completely pure, defects and holes will damage the impermeability of the material. The gravia project uses ALD and CVD to manufacture large area single-layer graphene sheets, and repeatedly deposits multi-layer graphene sheets, because single-layer graphene sheets can never be perfect, and multi-layer stacking structure can reduce defects and holes as much as possible. The researchers said that the barrier layer is suitable at 10 nanometers (about 30 layers of graphene), maintaining high light transmittance (> 90%) and high elasticity while ensuring the barrier effect.
In the figure above, a and B are photos of graphene encapsulated OLED structures and devices (7×7 square centimeter, blue part is AMOLED component), C and D are photos of 1×1 square centimeter light-emitting OLED devices just completed (left) and one week later (right).
The researchers say their solution is comparable to existing commercial OLED packaging technologies. Although this proves that graphene packaging is effective for organic light-emitting diodes, whether it can be commercialized with low cost and mass production is still unknown.
The gravia project team is led by Cambridge University, and other members are CPI Institute, flexenable and National Physics Laboratory (NPL).