An electrically switchable dye-doped liquid crystal polarizer for organic light emitting-diode displays

A conventional polarizer for an organic light-emitting diode (OLED) display deteriorates light efficiency by blocking more than 50% of the emitted light from the OLED. The use of such a polarizer with a quarter-waveplate is inevitable to achieve an excellent dark state because it blocks the reflection of incoming ambient light to the OLED. However, when there is no incoming light outside of the display, the polarizer does not play a role of suppressing the reflection but sacrifices emitted light. In this study, we propose a switchable dye-doped liquid crystal (DDLC) that serves as a polarizer for strong ambient light in the voltage-off state, which effectively absorbs ambient light reflection from OLED electrodes. With the DDLC in the voltage-on state, it can be switched to a non-absorption state for weak ambient light, allowing the emitted light from the OLED to pass through it, which enhances the light efficiency of the OLED. Consequently, the switchable DDLC performs effectively in terms of display contrast ratio and light efficiency for any ambient light conditions. The 2 wt% DDLC polarizer not only exhibits a smaller reflectance than that of a conventional polarizer, but also improves the emission intensity by 61%. Our proposed DDLC polarizer can be compactly equipped with an OLED panel and can improve the lifetime of the device by enhancing optical efficiency.