Transparent-cathode for top-emission organic light-emitting diodes

Abstract

A transparent-charge-injection layer consisting of LiF/Al/Al-doped SiO has been developed as (i) a cathode for top-emitting organic light-emitting diodes and as (ii) a buffer layer against damages induced by energetic ions generated during deposition of other functional thin films by sputtering, or plasma-enhanced chemical vapor deposition. A luminance of $\text{1900\hspace{0.17em}}{\mathrm{cd/m}}^2$ and a current efficiency of 4 cd/A have been achieved in a simple testing device structure of indium tin oxide (ITO) ${\mathrm{N,N}}^{\prime }$ -diphenyl-${\mathrm{N,N}}^{\prime }$ -bis(3-methylphenyl)-${\text{1,1}}^{\prime }$ -biphenyl-${\text{4,4}}^{\prime }$ -diamine $\text{(60\hspace{0.17em}}\mathrm{nm}\mathrm{)/}{\mathrm{Alq}}_3$ (40 nm)/LiF (0.5 nm)/Al (3 nm)/Al-doped SiO (30 nm). A minimum thickness of 30 nm of Al-doped SiO is also found to protect organic layers from ITO sputtering damage.