Red emissive organic light-emitting diodes based on codeposited inexpensive CuI complexes

Abstract

Inexpensive materials made of abundant natural resources such as Cu^I complexes are essential to sustain the development of organic light emitting diode (OLED) technology for mass market applications such as solid-state illumination. Cu^I complexes, however, mostly are neither soluble nor stable toward sublimation, which is a road block for the development of efficient Cu^I complex based OLEDs using traditional methods of synthesis, sublimation and vacuum evaporation. In this work, two isoquinolyl carbazole (CIQ) compounds 9-(8-(carbazol-9-yl)isoquinolin-5-yl)-carbazole (DCIQ) and 9-(4-(5-(4-(carbazol-9-yl)phenyl)isoquinolin-8-yl)phenyl)-carbazole (DCDPIQ) were synthesized to codeposition with copper iodide (CuI) to form red emissive dimeric Cu^I complex doped film in situ, which could be utilized directly as the emissive layer (EML) in OLEDs. After a systematic study of the two compounds and their codeposited CuI : CIQ films, as well as optimizing the CuI doping concentration, it is found that red OLEDs can be achieved, showing a maximum emission band, an external quantum efficiency (EQE), a luminance of 643 nm, 3.5%, 3290 cd m⁻² for DCIQ, and 635 nm, 3.6%, 853 cd m⁻² for DCDPIQ, respectively.