Transparent stacked organic light emitting devices. II. Device performanceand applications to displays

Vertical stacking of organic light emitting devices (OLEDs) that emit the t hree primary colors is shown to be a means for achieving efficient and brig ht full-color displays. In Paper I, we addressed stacked OLED (SOLED) desig n and fabrication principles to optimize emission colors, operating voltage , and efficiency. Here, we present results on two different (metal-containi ng and metal-free cathode) SOLED structures that exhibit performance suitab le for many full-color display applications. The operating voltages at 10 m A/cm(2) (corresponding to video display brightnesses) are 6.8, 8.5, and 12. 1 V for the red (R), green (G), and blue (B) elements of the metal-containi ng SOLED, respectively. The respective subpixel luminous efficiencies are 0 .53, 1.44, and 1.52 cd/A, and the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates are (0.72, 0.28), (0.42, 0.56), and (0.20, 0 .22). In the high transparency metal-free SOLED, an insulating layer was in serted between the two upper subpixels to allow for independent grounding o f all color emitters in the stack. At operating voltages of 12-14 V, video display brightnesses were achieved with luminous efficiencies of 0.35, 1.36 , and 1.05 cd/A for the R, G, and B subpixels, respectively. The respective CIE coordinates for R, G, and B emissions are (0.72, 0.28), (0.26, 0.63), and (0.17, 0.28) in the normal viewing direction, shifting inperceptibly as the viewing angle is increased to as large as 60 degrees. Finally, we disc uss addressing schemes of SOLED displays, and compare them with other strat egies for achieving full-color, OLED-based displays. (C) 1999 American Inst itute of Physics. [S0021-8979(99)03220-X].