Orgainic light emitting devices with silicon oxy-nitride buffer layer


Student thesis: Master's Thesis

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  • Chung On POON


Awarding Institution
Award date4 Oct 2004


The use of silicon oxy-nitride (SiOxNy) as an anode buffer layer in organic light-emitting devices (OLEDs) with a configuration of indium tin oxide (ITO)/SiOxNy/α-naphtylphenyliphenyl diamine (NPB)/8-hydroxyquinoline aluminum (Alq3)/Mg:Ag has been studied. With a SiOxNy buffer layer of several angstroms thick, the device current efficiency increased from 3.0 to 3.8 cd/A. Further, the buffer layer also protected the ITO surface from deleterious contamination due to air exposure. Upon exposing the cleaned ITO substrate to air for one day before device fabrication, the device current efficiency and turn-on voltage degraded to 2.1 cd/A and 4.3V respectively from 3 cd/A and 3.3V for the device fabricated on as-cleaned ITO surface. In contrast, devices prepared on air-exposed SiOxNy/ITO surface had almost the same current efficiency (3.8cd/A) and turn on voltage (3.7V) comparing to devices (3.85cd/A and 3.7V) fabricated on freshly prepared SiOxNy/ITO surface. The results suggested that SiOxNy is a promising anode buffer layer for OLED for both efficiency and surface stability enhancements. Also, the stability of device after inserting silicon oxy-nitride was also significantly improved. The lifetime of ITO standard device was about 600 hours with initial luminance of 465 cd/m2. However, after inserting SiOxNy with 0.2 standard cubic centimeters, the device still has 80% of initial luminance with 515 cd/m2 after operating 900 hours, and the atomic force microscopy (AFM) result shows that the rough mean square (r.m.s) roughness of buffer layer is smooth when compare with the ITO surface. Also, there is no damage when depositing the SiOxNy buffer layer on the pillar and base structure (passive matrix addressing) by radio frequency (r.f) magnetron sputtering method. The results indicate that SiOxNy is a good choice as an anode buffer layer in order to improve the device performance and stability and it can be applied in OLED display technologies.

    Research areas

  • Materials, Optical properties, Light emitting diodes, Silicon, Silicon nitride