Researchers from the University of Toronto developed the world's most efficient OLED on plastic, which they say is comparable with the best glass-based OLEDs. They discovered that coating the plastic substrate with a 50-100 nano-meter thick layer of tantalum(V) oxide (Ta2O5), an advanced optical thin-film coating material enabled them to re-construct the high-refractive index property previously limited to heavy metal-doped glass:
The researchers say that to create a high-efficiency OLED you need a high-refractive-index (n <= 1.8) substrate (to enhance the outcoupling of trapped light in the device). Plastic substrates have a low refractive index (n <= 1.6). The researchers say that their method allows for a high-efficiency OLED that does not depend on a high-index substrate. They used a phosphorescent OLED, a high-index Ta2O5 optical coupling layer, electrically conductive gold layer and hole-injection MoO3 layer. All these components are collectively optimized to achieve high efficiency. The maximum external quantum efficiency reaches 63% for green, which remains as high as 60% at >10,000 cd/m–2.