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

Abstract

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 CsN3‐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 CsN3 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 n‐type 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‐i‐n and tandem OLEDs, as well as simplify the material handling for the vacuum deposition process.

High triplet energy n-type dopants for high efficiency in phosphorescent organic light-emitting diodes

“…The p-type or n-type doping increased the conductivity of the charge transport materials and reduced the driving voltage of the OLEDs [2]. In particular, the n-type doping was effective to reduce the driving voltage of OLEDs due to the low mobility of common electron transport materials [5][6][7]3,[8][9][10][11][12][13][14][15]. Several n-type doping materials have been used to increase the conductivity of the electron transport materials.…”

“…Alkali metals such as Cs and Li were typical n-type doping materials [5][6][7]3,8,9] and several derivatives of Cs or Li were also developed as the n-type doping materials, which include ionic compound [10][11][12] or organometallic complexes [13][14][15][16][17]. Cs 2-CO 3 [10], CsN 3 [11], and LiF [12] were reported as n-type doping materials and increased the conductivity of an electron transport layer, decreasing the driving voltage of OLEDs. However, the ionic compounds quenched the excitons in the emitting layer and had negative effect on the quantum efficiency of OLEDs.…”

“…There have been several approaches to lower the driving voltage of OLEDs and one of the most well-known methods was to use p-type or n-type doped charge transport layers [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The p-type or n-type doping increased the conductivity of the charge transport materials and reduced the driving voltage of the OLEDs [2].…”

Role of hole injection layer in intermediate connector of tandem organic light-emitting devices

“…In most cases, the intermediate connectors compose of ''n-type doped layer/p-type doped layer'' and ''n-type doped layer/electron acceptor/hole transporting layer'' [4][5][6][7][8][9]. The n-type doped layer is formed by doping an electron transporting material with an n-type dopant, such as the alkaline/alkaline-earth metal or the alkaline/alkalineearth compound (e.g., Li 2 CO 3 , Cs 3 PO 4 , Cs 2 CO 3 , CsN 3 , KBH 4 , LiNH 2 ) [4][5][6][7][8]10].…”

“…The n-type doped layer is formed by doping an electron transporting material with an n-type dopant, such as the alkaline/alkaline-earth metal or the alkaline/alkalineearth compound (e.g., Li 2 CO 3 , Cs 3 PO 4 , Cs 2 CO 3 , CsN 3 , KBH 4 , LiNH 2 ) [4][5][6][7][8]10]. The p-type doped layer is formed by doping a hole transporting material with an electron acceptor having a deep lying unoccupied state, such as tetrafluorotetracyanoquinodimethane (F4-TCNQ), 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN), or the transitional metal oxide (e.g., MoO 3 , WO 3 , V 2 O 5 , etc.)…”