Highly efficient tandem p-i-n organic light-emitting diodes adopting a low temperature evaporated rhenium oxide interconnecting layer

High quality interconnection units (ICUs) with a high transparency and superior charge generating capability for tandem organic light-emitting diodes (OLEDs) are developed. The ICUs of rubidium carbonate-doped 4,7-diphenyl-1,10- phenanthroline/rhenium oxide (Re O3) -doped N, N′ -diphenyl- N, N′ -bis(1, 1′ -biphenyl)- 4, 4′ -diamine layers with or without an additional Re O3 interlayer produce high transmittance (88%-92% at 420-700 nm) and spontaneous internal charge generation properties. A very high efficiency of ∼129 cdA has been demonstrated from only two stacked green p-i-n OLEDs by employing the developed ICUs. The relationship between the device efficiency and internal charge generation within the ICUs is further described by means of the capacitance measurements.