Methodology for optimizing viewing characteristics of top-emitting organic light-emitting devices

Abstract

Top-emitting organic light-emitting devices ͑OLEDs͒ have a few technical merits for active-matrix OLED displays. Generally stronger microcavity effects inherent in top-emitting OLEDs, however, complicate optimization of device efficiency and other viewing characteristics. In this letter, using the rigorous classical electromagnetic model, we analyze emission characteristics of top-emitting OLEDs as a function of device structures. From the comprehensive analysis, trends in the dependence of emission characteristics on device structures are extracted, and accordingly, a general methodology for optimizing viewing characteristics of top-emitting OLEDs for display applications is suggested. The effectiveness of the analysis and the methodology is confirmed by experimental results.

Optimization of the efficacy and angle dependence of emission of top-emissive organic light-emitting diodes on metal foils

“…As a result, spectral narrowing and an increased angle dependence of the electroluminescence are obtained, which are hard to optimize simultaneously. 22 …”

“…These are all similar trends to those observed when optimizing top-emissive OLEDs fabricated on smooth glass substrates. 22 Typically it is seen that it is very difficult to simultaneously achieve a maximum in the efficacy and a minimum in the variation of color and luminance with viewing angle in topemissive devices, since the optimal layer thicknesses for the best efficacy and the best color performance are usually different. 22 In the system that we investigated on stainless steel foil we do actually achieve a coincidence of the maximum efficacy of 9.8 lm/A and a Lambertian emission profile for the same PEDOT layer thickness of 40 nm.…”

“…22 Typically it is seen that it is very difficult to simultaneously achieve a maximum in the efficacy and a minimum in the variation of color and luminance with viewing angle in topemissive devices, since the optimal layer thicknesses for the best efficacy and the best color performance are usually different. 22 In the system that we investigated on stainless steel foil we do actually achieve a coincidence of the maximum efficacy of 9.8 lm/A and a Lambertian emission profile for the same PEDOT layer thickness of 40 nm. For comparison, the efficacy of bottom-emissive devices on glass made with the same blue-emitting LEP is 16.3 lm/A (2.4lm/W) and there is a far lower variation in device performance when the PEDOT layer thickness is changed.…”

“…Both the PEDOT and LEP thicknesses allow adjustment of the optical cavity, but varying the LEP thickness is a more complicated approach as other parameters such as the electrical field strength and thus recombination zone are also affected. 22 We have also kept the cathode material layer thicknesses constant during our investigation. As described in Sec.…”

High-efficiency transparent organic light-emitting diode with one thin layer of nickel oxide on a transparent anode for see-through-display application

“…The methodology for optimizing viewing characteristics of top-emitting OLEDs has been presented [10,11]. In this paper, we have designed a TOLED with a symmetric structure, in which two metal layers was used next to the transparent electrodes and functioned as a hole injection and an electron injection layer, respectively.…”