Nanodot‐Enhanced High‐Efficiency Pure‐White Organic Light‐Emitting Diodes with Mixed‐Host Structures

Abstract

A relatively high‐efficiency, fluorescent pure‐white organic light‐emitting diode was fabricated using a polysilicic acid (PSA) nanodot‐embedded polymeric hole‐transporting layer (HTL). The diode employed a mixed host in the single emissive layer, which comprised 0.5 wt % yellow 5,6,11,12‐tetra‐phenylnaphthacene doped in the mixed host of 50 % 2‐(N,N‐diphenyl‐amino)‐6‐[4‐(N,N‐diphenylamino)styryl]naphthalene and 50 % N,N′‐bis‐(1‐naphthyl)‐N,N′‐diphenyl‐1,10‐biphenyl‐4‐4′‐diamine. By incorporating 7 wt % 3 nm PSA nanodot into the HTL of poly(3,4‐ethylene‐dioxythiophene)‐poly‐(styrenesulfonate), the efficiency at 100 cd m–2 was increased from 13.5 lm W–1 (14.7 cd A–1; EQE: 7.2 %) to 17.1 lm W–1 (17.6 cd A–1; EQE: 8.3 %). The marked efficiency improvement may be attributed to the introduction of the PSA nanodot, leading to a better carrier‐injection‐balance.

Extraordinarily High Efficiency Improvement for OLEDs with High Surface-Charge Polymeric Nanodots

“…In addition, the resultant higher device efficiency could somewhat reduce heat generated upon emission, preventing damage caused by the generation of excessive heat during operation. 10,33,35 Moreover, as discussed above, the incorporation of Am-PND can enlarge the width of the recombination zone, resulting in an increase in the device lifetime. 33…”

“…Polymeric nanodots (PNDs) are effective in improving the device efficiency of organic light-emitting diodes that are suitable for high-quality displays and area illumination. − In contrast to electrically neutral quantum dots and nanodots used in dry processes, polymeric nanodots can be synthesized with a precisely controlled size and wet-processed on soft substrates. This benefit from polymeric nanodots enables the realization of the large-area, roll-to-roll fabrication of flexible displays and lighting devices. − To replace current display technologies and illumination measures, such as incandescent bulbs and fluorescent tubes, the existing nanodots can be modified to improve their carrier-modulation capability and produce higher device efficiency. − Here we demonstrate a general method that substantially advances the efficiency of highly efficient organic light-emitting diodes (OLEDs) of all emissive colors, including white, via the incorporation of highly charged polymeric nanodots that are capable of modulating the transport flux of holes in the hole-injection layer effectively. One such example is the blue OLED, which has an initially high power efficiency of 18.0 lm W −1 at 100 cd m −2 ; the efficiency of the blue OLED was doubled to 35.8 lm W −1 when an amino-functionalized PND was employed.…”

Solution-Process-Feasible Deep-Red Phosphorescent Emitter

“…From material perspective, phosphorescent as well as TADF emitters are attracting increasing attention due to their high quantum efficiency. From a device structure perspective, they include the employment of low interfacial resistance P–I–N structures, − low carrier-injection barriers, − balanced carrier injection, − carrier and exciton confinement, − stepwise emissive layers, carrier modulation layers, , structures enabling exciton to generate on host or on both host and guest, structures facilitating host-to-guest energy transfer,and co-host structures. − From a light out-coupling perspective, the efficiency enhanced techniques include the employment of macroextractors, microlens thin-film arrays, photonic crystals, structured substrate surfaces, high refractive index glass, and low refractive index layers, as well as reduction of metal surface plasmons and orientation control of the molecular dipoles . Nevertheless, employing a highly efficient phosphorescent emitter in well-engineered devices is the most determinant factor in achieving high efficiency.…”

Enabling high-efficiency organic light-emitting diodes with a cross-linkable electron confining hole transporting material

“…47 For a high triplet energy blue emitter containing device, it is increased from 6.9 to 8.9 lm W À1 , an incre- 48 ment of 29%, and the maximum luminance enhanced from 9000 to 11,000 cd m À2 , an increment of 22%. Organic light-emitting diodes (OLEDs) have attracted much 55 attention due to their potential in high quality full-color displays 56 and solid-state lighting applications [1][2][3][4][5][6][7][8][9][10][11]. In order to expand 57 their applicability, new fabrication techniques are constantly being 58 developed.…”