Solution-processable organic light-emitting diodes utilizing electroluminescent perylene tetraester-based columnar liquid crystals.

Abstract

Herein, we reveal a homologous series of liquid crystals involving perylene tetraesters as the core connected to the four trialkoxyphenyl units at the periphery using the triazole moiety as the linker. A thorough analysis using differential scanning calorimetry, polarized optical microscopy, and small- and wide-angle X-ray scattering studies confirm that all the mesogens 1a-c hold a stable enantiotropic columnar mesophase. Suitable molecular orbital levels and excellent material photophysical and thermal properties encouraged the study of their electroluminescent properties. Due to this, a well designed solution-processable organic light emitting diode device structure is configured as ITO (125 nm)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (35 nm)/host: <i>x</i> wt% emitter (<i>x</i> = 0.5, 1.0, 3.0, 5.0) (20 nm)/2,2'2''-(1,3,5-benzinetriyl)tris(1-phenyl-1-<i>H</i>-benzimidazole) (TPBi) (40 nm)/lithium fluoride (LiF) (1 nm)/aluminium (Al) (200 nm) using compounds 1a-c as emitters. 4,4',4''-Tris[phenyl(<i>m</i>-tolyl)amino]triphenylamine (<i>m</i>-MTDATA) and 4,4'-bis(<i>N</i>-carbazolyl)-1,1'-biphenyl (CBP) were chosen as two different host materials. The current density-voltage-luminance and current efficacy-luminance-power efficacy plots suggest that <i>m</i>-MTDATA is a better host than CBP. Amongst, device based on 1 wt% emitter 1c doped in the <i>m</i>-MTDATA host matrix displayed the best performance, with a maximum power efficacy of 17.2 lm W^-1, current efficacy of 18.5 cd A^-1, and external quantum efficiency of 6.3%.