Micro-cavity organic light emitting diodes for biochip applications

Vertical and transverse confinement of electromagnetic radiation in planar organic light emitting diodes (OLED) has been widely addressed in order to maximize their external quantum efficiency. Here we propose a planar micro-cavity OLED with the aim to tailor the angular emission pattern and obtain light emission suppression in the vertical direction. Vertical confinement was obtained by depositing a conventional molecular OLED on a glass substrate coated with a thin gold semitransparent layer and a silica spacer. The conventional OLED was obtained by depositing under vacuum an indium tin oxide hole-injection layer, an organic hetero-junction constituted by N,N-diphenyl-N,N-bis(3-methyl phenyl)-1,1-biphenyl-4,4-diamine (TPD) and tris(8-hydroxy-quinoline)-aluminium (Alq3) layers and a LiF/Al electron-injection layer. Performance of the micro-cavity OLEDs was characterized by measuring the current/voltage characteristics and the angular dependence of the brightness and emission spectrum. The results were compared to those obtained for reference conventional OLEDs, without vertical confinement. Suppression of the green emission in the vertical direction was observed, confirming what was expected by calculations of dipole emission in a micro-cavity structure.