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 (CsN 3 ) is employed as a novel n‐dopant because of its air stability and low deposition temperature. CsN 3 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 MoO 3 ‐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 N 2 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 CsN 3 ‐doped n‐type organic layer/MoO 3 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‐i‐n and tandem OLEDs, as well as simplify the material handling for the vacuum deposition process.