Tailoring carrier injection efficiency to improve the carrier balance of solid-state light-emitting electrochemical cells

Chih Teng Liao, Hsiao Fan Chen, Hai-Ching Su*, Ken Tsung Wong

*此作品的通信作者

研究成果: Article同行評審

45 引文 斯高帕斯(Scopus)

摘要

We study the influence of the carrier injection efficiency on the performance of light-emitting electrochemical cells (LECs) based on a hole-preferred transporting cationic transition metal complex (CTMC) [Ir(dfppz) 2(dtb-bpy)] +(PF 6 -) (complex 1) and an electron-preferred transporting CTMC [Ir(ppy) 2(dasb)] +(PF 6 -) (complex 2) (where dfppz is 1-(2,4-difluorophenyl) pyrazole, dtb-bpy is 4,4′-di(tert-butyl)- 2,2′-bipyridine, ppy is 2-phenylpyridine and dasb is 4,5-diaza-9,9′- spirobifluorene). Experimental results show that even with electrochemically doped layers, the ohmic contacts for carrier injection could be formed only when the carrier injection barriers were relatively low. Thus, adding carrier injection layers in LECs with relatively high carrier injection barriers would affect carrier balance and thus would result in altered device efficiency. Comparison of the device characteristics of LECs based on complex 1 and 2 in various device structures suggests that the carrier injection efficiency of CTMC-based LECs should be modified according to the carrier transporting characteristics of CTMCs to optimize device efficiency. Hole-preferred transporting CTMCs should be combined with an LEC structure with a relatively high electron injection efficiency, while a relatively high hole injection efficiency would be required for LECs based on electron-preferred transporting CTMCs. Since the tailored carrier injection efficiency compensates for the unbalanced carrier transporting properties of the emissive layer, the carrier recombination zone would be located near the center of the emissive layer and exciton quenching near the electrodes would be significantly mitigated, rendering an improved device efficiency approaching the upper limit expected from the photoluminescence quantum yield of the emissive layer and the optical outcoupling efficiency from a typical layered light-emitting device structure. This journal is

原文English
頁(從 - 到)9774-9784
頁數11
期刊Physical Chemistry Chemical Physics
14
發行號27
DOIs
出版狀態Published - 21 7月 2012

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