Highly efficient p-i-n and tandem organic light-emitting devices using an air-stable and low-temperature-evaporable metal azide as an n-dopant

Cesium azide (CsN₃) is employed as a novel n-dopant because of its air stability and low deposition temperature. CsN₃ is easily co-deposited with the electron transporting materials in an organic molecular beam deposition chamber so that it works well as an n-dopant in the electron transport layer because its evaporation temperature is similar to that of common organic materials. The driving voltage of the p-i-n device with the CsN ₃-doped n-type layer and a MoO₃-doped p-type layer is greatly reduced, and this device exhibits a very high power efficiency (57 lm W^-1). Additionally, an n-doping mechanism study reveals that CsN ₃ was decomposed into Cs and N₂ during the evaporation. The charge injection mechanism was investigated using transient electroluminescence and capacitance-voltage measurements. A very highly efficient tandem organic light-emitting diodes (OLED; 84 cd A_-1) is also created using an n-p junction that is composed of the CsN₃-doped ntype organic layer/MoO₃ p-type inorganic layer as the interconnecting unit. This work demonstrates that an air-stable and low-temperature-evaporable inorganic n-dopant can very effectively enhance the device performance in p-in and tandem OLEDs, as well as simplify the material handling for the vacuum deposition process.