Tandem Organic Light‐Emitting Diode using Hexaazatriphenylene Hexacarbonitrile in the Intermediate Connector

Abstract

Organic light-emitting diodes have been attracting a great deal of attention because they are useful for applications as next-generation displays and for solid-state lighting. [1,2] An OLED is actually a current-driven device, and its luminance increases with increasing current density. However, the operational lifetime of an OLED decreases with increasing current density. [3] In order to achieve high brightness, an OLED must be operated at a relatively high current density, but this will result in a short lifetime. Thus, it is crucial to improve the luminous efficiency of an OLED while operating at the lowest possible current density consistent with the intended luminance requirement to increase the operational lifetime. In order to dramatically improve the luminous efficiency and to increase the lifetimes of OLEDs, a tandem (or stacked) OLED structure can be fabricated. This is accomplished by vertically stacking several individual electroluminescent (EL) units, each with a hole-transporting layer (HTL)/light-emitting layer (LEL)/electron-transporting layer (ETL) structure, with the entire device driven by a single power source. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In a tandem OLED with N EL units (N > 1), the luminous efficiency can be about N times as high as that of a conventional OLED that contains only one EL unit (the drive voltage will also be about N times as high as that of the conventional OLED). Therefore, the tandem OLED needs only about 1/N times the current density used in the conventional OLED to obtain the same luminance, which results in an operational lifetime N times that of the conventional OLED. Alternatively, the tandem OLED can achieve a luminance N times higher than that of the conventional OLED while maintaining about the same lifetime. In a tandem OLED, all of the EL units are electrically connected in series by inserting an intermediate connector (or connecting unit) between adjacent EL units. The intermediate connector plays an important role in the function of tandem OLEDs. The intermediate connector can be formed using a metal-metal (or metal oxide) bilayer, [4,11] an organic-metal (or metal oxide) bilayer, [5,6,7,9,10,[12][13][14]16,17] or an organic-organic bilayer. [6,8,15,[18][19][20] Using a metal or a metal oxide in an intermediate connector can introduce fabrication complexity. Many kinds of metals and metal oxides cannot be deposited by thermal evaporation at a temperature below 300°C; hence, methods for their deposition are not usually compatible with the underlying organic layers. Additionally, metals and some metal oxides can cause pixel crosstalk in dot-matrix displays and low optical transparency. In contrast, organic-organic intermediate connectors can be formed using thermal evaporation methods with relatively low evaporation temperatures, and they do not cause pixel crosstalk or low optical transparency.In the organic-organic intermediate connector, the first organic layer is an n-type doped organic layer, such as an alkali metal-doped ETL....

Emission Characteristics of Blue Fluorescence Tandem OLED Using MoOx

“…그러나 OLED는 아직까지 상업적 인 디스플레이 소자와 비교하여 낮은 효율을 가지 고 있다. 이러한 문제점을 극복하기 위하여 발광휘 도, 발광효율, 소자의 수명과 발광 스펙트럼의 변화 를 줄 수 있는 특징이 있는 적층형 유기발광소자 (Tandem OLED)에 관한 연구가 이루어지고 있다 [6][7][8][9][10] . 적층형 OLED란 두 개 이상의 단일구조 OLED 사 이에 전자와 정공의 산화환원반응으로부터 전자와 정 공이 생성되는 전하생성층 (Charge Generation Layer ; CGL)을 삽입하여 제작한 OLED이다.…”

Hexaazatriphenylene (HAT) versus tri‐HAT: The Bigger the Better?

“…Thus, several contributions focused on various characteristics of these materials, such as their liquid-crystal behavior, [7][8][9][10][11][12][13][14] their tendency to self-assemble in solution and on different surfaces, [15][16][17][18][19][20][21][22][23][24][25] or their redox properties. [26][27][28] Their application to modify and control the color of mesoporous silica [29] and their inclusion in organic light-emitting devices [30,31] have been described as well.…”

Rhenium oxide as the interfacial buffer layer for polymer photovoltaic cells

“…However, their toxicity and high evaporation temperature hinder their practical application in polymer solar cells. ReO 3 can be evaporated at a lower temperature (~340 o C) than MoO 3 , alleviating the drawbacks of metal oxides in a practical manufacturing process induced by a high evaporation temperature [16] . Moreover, the ReO 3 material has high work function of about 6.0 eV.…”