Highly efficient tandem white organic light-emitting diodes based upon C ₆₀/NaT4 organic heterojunction as charge generation layer

We present a high-efficiency tandem white organic light-emitting diode based upon a C ₆₀/5,5′′′-bis(naphth-2-yl)-2, 2′:5′,2′′:5′′,2′′′- quaterthiophene (NaT4) organic heterojunction as a charge generation layer. A maximum current efficiency, maximum power efficiency, and maximum external quantum efficiency of 111.3 cd A ^-1, 50.5 lm W ^-1, and 38.7%, respectively, are obtained. More importantly, the efficiency roll-off is greatly improved with only a slight roll-off to109 cd A ^-1, 40.3 lm W ^-1, and 38% at a luminance of 1000 cd m ^-2. Surprisingly, the electroluminescent spectrum is highly stable at all levels of luminance. Furthermore, our tandem device shows better operational stability than a tandem device employing a conventional charge generation layer. It is concluded that the excellent charge generation, transport, and extraction in the C ₆₀/NaT4 organic heterojunction-based CGL is responsible for the high performances.