Highly efficient ultra-flexible tandem organic light-emitting diodes adopting a non-doped charge generation unit

Due to the voltage division of charge generation unit (CGU), the power efficiency of tandem organic light-emitting diodes (TOLEDs) is usually lower than that of the single-unit devices, which severely restricts the development and application of TOLEDs. Here, a significant improvement in power efficiency of TOLEDs is presented through adopting a non-doped CGU of LiF/Al/fullerene (C60)/1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN)/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB). The characteristics of current–voltage and impedance spectroscopy reveal that the non-doped CGU possesses fabulous charge generation and injection capabilities. The ultra-flexible tandem white OLEDs display a maximum power efficiency of 59 lm W−1, which is 32% higher than that of single white OLEDs. What's more meaningful, the ultra-flexible devices have good mechanical flexibility and durability. After being bent for 3000 cycles at a radius of ∼3 mm, the devices retain ∼90% of the original luminance.