Enhancing Optical Out‐Coupling of Organic Light‐Emitting Devices with Nanostructured Composite Electrodes Consisting of Indium Tin Oxide Nanomesh and Conducting Polymer

Abstract

A nanostructured composite electrode consisting of a high-index indium-tin-oxide nanomesh and low-index high-conductivity conducting polymer effectively enhances coupling of internal radiation of organic light-emitting devices into their substrates. When combining this internal extraction structure and the external extraction scheme, a very high external quantum efficiency of nearly 62% is achieved with a green phosphorescent device.

Three‐dimensional pixel configurations for optical outcoupling of OLED displays—optical simulation

“…ITO (10 nm)/Ag (150 nm)/ITO (10 nm) is the common reflective bottom electrode used for top‐emitting AMOLEDs in the industry. HATCN [dipyrazino[2,3‐f:2′,3′‐h]quinoxaline2,3,6,7,10,11‐hexacarbonitrile] serves as the hole injection layer (HIL), and NPB [ N , N ′‐di(1‐naphthyl)‐ N , N ′‐diphenyl‐(1,1′‐biphenyl)‐4, 4′‐diamine] serves as hole transport layer (HTL) . mCBP [3,3′‐di(9H‐carbazol‐9‐yl)biphenyl] doped with 8 wt% Ir (ppy) 2 (acac) [bis(2‐phenylpyridine)(acetylacetonato) iridium(III), assuming horizontal emitting dipole ratio of 76%] is the phosphorescent green emitting layer (EML) .…”

“…mCBP [3,3′‐di(9H‐carbazol‐9‐yl)biphenyl] doped with 8 wt% Ir (ppy) 2 (acac) [bis(2‐phenylpyridine)(acetylacetonato) iridium(III), assuming horizontal emitting dipole ratio of 76%] is the phosphorescent green emitting layer (EML) . TPBi (2,2′,2″‐(1,3,5‐benzinetriyl)‐tris(1‐phenyl‐1‐H‐benzimidazole)) is the electron transport layer (ETL) . Two types of top electrode structures were studied: (1) LiF (1 nm)/Mg/Ag = 1:9 (20 nm)/NPB (65 nm), where LiF is the electron injection layer (EIL), Mg/Ag = 1:9 is the cathode, and NPB is the capping layer, and (2) HATCN (30 nm)/ITO (80 nm), for which high‐electron‐affinity HATCN serves as the buffer layer for ITO deposition and also to form the tunneling p‐n junction with the n‐doped ETL TPBi (a portion of ETL TPBi being assumed doped by n‐type conductive dopants for effective electron injection from ITO to ETL) .…”

“…However, ϕ out is still one of the limiting factors for pursing high EQE for current OLED displays. Over the years, various light extraction approaches had been reported for OLEDs, such as microlens arrays, photonic crystals, and scattering layers . Although these techniques may be useful for OLED lighting, they however are not so applicable to (top‐emitting) active‐matrix OLED displays (AMOLEDs) because of considerations on image quality and fabrication/integration compatibility.…”

“…Over the years, various light extraction approaches had been reported for OLEDs, such as microlens arrays, photonic crystals, and scattering layers. [3][4][5][6][7][8][9][10][11][12][13][14] Although these techniques may be useful for OLED lighting, they however are not so applicable to (top-emitting) active-matrix OLED displays (AMOLEDs) because of considerations on image quality and fabrication/integration compatibility. Thus to date, AMOLEDs still hardly adopt any effective light outcoupling techniques/structures, and it remains a significant technical issue for pursuing low-power-consumption AMOLED displays.…”

A Vision toward Ultimate Optical Out‐Coupling for Organic Light‐Emitting Diode Displays: 3D Pixel Configuration

“…Assuming the intrinsic emission spectrum and isotropic emitting dipole orientation (i.e., with a horizontal dipole ratio‐HR of 67%) of a typical green phosphorescent emitter Ir(ppy) 3 for the EML,26, 31 Figures S4 and S5 in the Supporting Information show that the optimal light extraction efficiencies η ext of ≈25–26% and ≈30% can be obtained with HTL/ETL of ≈200–205/60–65 nm for thin Ag and ITO devices, respectively. It is noted that higher extraction efficiencies are obtained with locating emitters at the second antinode position relative to the bottom reflective electrode (i.e., thicker HTL), mainly due to suppression of SPP loss to that metal contact 13, 30, 31.…”