Recently, ‘Liquid crystal display (LCD) vs. organic light-emitting diode (OLED) display: who wins?’ has become a topic of heated debate. In this review, we perform a systematic and comparative study of these two flat panel display technologies. First, we review recent advances in LCDs and OLEDs, including material development, device configuration and system integration. Next we analyze and compare their performances by six key display metrics: response time, contrast ratio, color gamut, lifetime, power efficiency, and panel flexibility. In this section, we focus on two key parameters: motion picture response time (MPRT) and ambient contrast ratio (ACR), which dramatically affect image quality in practical application scenarios. MPRT determines the image blur of a moving picture, and ACR governs the perceived image contrast under ambient lighting conditions. It is intriguing that LCD can achieve comparable or even slightly better MPRT and ACR than OLED, although its response time and contrast ratio are generally perceived to be much inferior to those of OLED. Finally, three future trends are highlighted, including high dynamic range, virtual reality/augmented reality and smart displays with versatile functions.
High‐efficiency organic light emitting diodes (OLEDs) are fabricated using a group of benzimidazole‐carbazole derivatives with good molecular packing as hosts. The hosts are separately doped with a green thermally activated delayed fluorescence (TADF) emitter, 1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6‐dicyanobenzene (4CzIPN). An ultralow concentration (0.5% volume ratio) of 4CzIPN is required in the emitting layer (EML) to achieve a record‐high external quantum efficiency of 31.8% by comparison with reported 4CzIPN‐relative devices. This result is attributed to efficient energy transfer, alleviation of concentration quench of 4CzIPN, long‐distance triplet exciton diffusion ability of host materials, and excellent horizontal molecular packing. With an increase in dopant concentration from 0.5% to 15%, the diodes exhibit a tiny variation in power efficiencies (82.9−78.7 lm W−1) and current efficiencies (92.2−87.5 cd A−1). In particular, the long‐distance triplet exciton diffusion ability of hosts exceeds the typical distance limitation (less than 10 Å) of Dexter energy transfer. Thus, high‐efficiency OLEDs are obtained with the scarce dopants . The aforementioned long‐distance triplet diffusion results are verified by the almost‐identical high‐efficiency device performances and the longer delayed emission lifetime in transient electroluminescence signals of a series of partially doped devices, conducting by separately doping low‐concentration TADF emitters in different EML regions.
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