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Li : Mg alloy with variable work function as highly efficient cathode for organic light‐emitting devices
Author(s) -
Miao Yuqi,
Xie Kai,
Xiang Qian,
Xiong Zhihua,
Zhang Deqiang,
Duan Lian
Publication year - 2016
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201600361
Subject(s) - work function , alloy , materials science , cathode , x ray photoelectron spectroscopy , oled , evaporation , phase (matter) , analytical chemistry (journal) , doping , chemical engineering , optoelectronics , metallurgy , composite material , chemistry , metal , thermodynamics , organic chemistry , physics , layer (electronics) , engineering
In this work, Li : Mg alloys are formed by co‐evaporation of Li 3 N and Mg with different ratios and are used as cathode for organic light‐emitting didoes (OLEDs). Three phases of Li : Mg alloys can be observed by XRD measurements for Li : Mg alloys with 5, 20, and 50% molar ratio of Li, respectively. The XPS result reveals the charge transfer between Li and Mg, further confirming the formation of Li : Mg alloy. OLEDs with Li : Mg alloy as the cathode all show lower operating voltages and higher efficiencies than the control device using Mg : Ag cathode. For the Li : Mg alloy with 20% Li, the peak power efficiency is 2.23 lm W −1 , which is more than doubled compared with the control device (1.09 lm W −1 ). Quantum calculation has been carried out to get the surface work functions of different Li : Mg alloys. The 20% Li doped Li : Mg alloy possesses the lowest work function of 2.497 eV, leading to the lowest electron injection barrier and best device performance. We also find that the surface work function of the Li : Mg alloy would be affected by not only aggregation phase but also the surface distribution of crystal facets (preferential crystal orientation), which indicates that alloys showed anisotropy in work function, like elemental metals.