Improved light extraction efficiency with angle independent electroluminescence spectrum in nano-phosphor coated white organic light emitting diodes

We have fabricated down converted white organic light emitting diodes (WOLEDs) by using cerium doped YAG nano-phosphor after mixing them in binder poly venyle acetate (PVAc) polymer matrix by changing the concentration of nano-phosphor. Down conversion layer was deposited by using a low cost spin coating technique. The enhancement in extraction efficiency by a factor of about 1.6 was found comparable to other expansive techniques for the fabrication of down conversion layer. We have characterized WOLEDs for angle dependency of electroluminescence spectrum. The electroluminescence spectra at viewing angles from normal to the substrates up to 75° off normal remain almost unchanged and does not show the angle dependence observed for other extraction efficiency enhancement techniques. The emission spectrum was also found to be stable with time, which is a common problem with multilayer WOLED. The spectral uniformity with angle and time with enhanced extraction efficiency and cheap deposition technique could be of great interest for the application of down converted WOLED.