Long‐Lived Flexible Displays Employing Efficient and Stable Inverted Organic Light‐Emitting Diodes

Abstract

Although organic light-emitting diodes (OLEDs) are promising for use in applications such as in flexible displays, reports of long-lived flexible OLED-based devices are limited due to the poor environmental stability of OLEDs. Flexible substrates such as plastic allow ambient oxygen and moisture to permeate into devices, which degrades the alkali metals used for the electron-injection layer in conventional OLEDs (cOLEDs). Here, the fabrication of a long-lived flexible display is reported using efficient and stable inverted OLEDs (iOLEDs), in which electrons can be effectively injected without the use of alkali metals. The flexible display employing iOLEDs can emit light for over 1 year with simplified encapsulation, whereas a flexible display employing cOLEDs exhibits almost no luminescence after only 21 d with the same encapsulation. These results demonstrate the great potential of iOLEDs to replace cOLEDs employing alkali metals for use in a wide variety of flexible organic optoelectronic devices.

P‐169: Operationally Stable Blue Inverted OLEDs Employing Fluorescent Emitter

“…Thus, the EIL can be prepared by fabrication processes that might damage the organic layers, resulting in an enhanced range of materials suitable for EILs. If an inverted OLED is prepared without air-sensitive materials such as alkali metals, no stringent encapsulation is necessary for such an inverted OLED [4,5]. The main challenge in enhancing the performance of inverted OLEDs is EIL development since a large energy barrier for electron injection exists between the cathode and the organic layer [6].…”

“…In addition, to examine the effect of the original dopant, a conventional air-stable n-type dopant 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl) phenyl)dimethylamine (N-DMBI) [15] was used as a reference. Since the solution-processed organic EILs are suitable for demonstrating efficient and operationally stable inverted OLEDs [5], the organic EILs were all fabricated by a solution process. The other organic layers were sequentially deposited onto the substrate.…”

Universal Strategy for Efficient Electron Injection into Organic Semiconductors Utilizing Hydrogen Bonds

“…For this study, we selected widely used and easily available bases. Since the characteristics of iOLEDs strongly depend on the electron injection/transport property of the interlayer, information about the improved electron injection efficiency resulting from the addition of bases can be extracted from the base‐dependent iOLED characteristics . The host material used in the interlayer was spB‐BPy 2 , which is suitable for demonstrating operationally stable iOLEDs (Figure S1, Supporting Information).…”

“…In addition, some of the iOLEDs with base‐added interlayers exhibited higher operational stability than those with the pristine spB‐BPy 2 (Figure f), which suggests that the operational stability of these bases is high. The expected half‐lifetime of the best iOLEDs is over 20 000 h, which is the longest among the OLEDs reported containing Ir(piq) 3 (Figure S5, Supporting Information) . For comparative purposes, the interlayer was also doped with 4‐(2,3‐dihydro‐1,3‐dimethyl‐1 H ‐benzimidazol‐2‐yl)‐ N , N ‐dimethylbenzenamine (N‐DMBI) and a polyethylene imine, both of which improve the electron injection efficiency .…”

“…For comparative purposes, the interlayer was also doped with 4‐(2,3‐dihydro‐1,3‐dimethyl‐1 H ‐benzimidazol‐2‐yl)‐ N , N ‐dimethylbenzenamine (N‐DMBI) and a polyethylene imine, both of which improve the electron injection efficiency . Although these dopants were also effective for lowering the driving voltages of their corresponding iOLEDs, only the iOLED with a base‐added interlayer exhibited higher operational stability than that with an interlayer consisting of pristine spB‐BPy 2 (Figure S6, Supporting Information) . The high air stability of the base‐added iOLEDs was also confirmed by monitoring their degradation rate, which was found to be much lower for the iOLED having the DBN‐added interlayer than for the conventional OLED having lithium as the EIL and for the iOLED with the lithium‐complex‐doped interlayer (Figure S7, Supporting Information).…”