Thermally Evaporated Organic/Ag/Organic Multilayer Transparent Conducting Electrode for Flexible Organic Light‐Emitting Diodes

Abstract

flexibility. In recent times, several prototypes of the flexible display based on OLED have been reported. [2][3][4] However, there are still some issues related to the fabrication of flexible OLEDs. Among the main concerns, securing transparent conducting electrode (TCE) with high mechanical flexibility as well as durability and good thermal stability are the most important issue. Generally, widely used TCE, Indiumtin-oxide (ITO) is not suitable for flexible display applications despite high transparency and conductivity due to its high rigidity. Therefore, to replace ITO, various types of flexible TCEs such as conducting metal oxide, [5][6][7] metal nanowire, [8,9] metal mesh, [10,11] carbon nanotube, [12,13] graphene, [14,15] and conducting polymers [16,17] have been reported.An ultrathin metal layer or sputter coinage metal, especially silver (Ag), with a thickness of about 10-14 nm is one of the noteworthy and alternative flexible TCEs because of its high transparency and low sheet resistance. The high ductility of the ultrathin metal layer makes it a flexible electrode to ensure high durability against the mechanical deformations. Moreover, it has a simple fabrication process which includes thermal deposition at room temperature using a fine metal mask without any patterning process for instance photo lithography. However, sole ultrathin Ag film with low resistivity and good uniformity cannot be formed accurately due to the Ag agglomeration, which induced by the stronger cohesion force between Ag clusters than the adhesion force of metal-substrate interface. [18][19][20][21] Typically, the Ag agglomeration aggravates the sheet resistance property owing to incomplete electrical path connection, as a result, low transmittance at the thickness of Ag with sufficiently low sheet resistance. To overcome this, metal oxide-based dielectricmetal-dielectric multilayer structures have been largely developed for optoelectronic devices. [22][23][24][25][26][27] Normally, the metal oxide-based binding/seed layer can reduce the coalescence between Ag clusters by increasing the interface adhesion force according to the bonding formation between Ag and oxygen. [21] However, metal oxide, especially molybdenum This paper reports an efficient, thermally stable, and high-performance flexible multilayer transparent conducting electrode (TCE) by sandwiching an ultrathin Ag layer between a thermally evaporated small-molecule organic wetting inducer, 1,4-bis(2-phenyl-1,10-phenanthrolin-4-yl)benzene and an organic antireflective capping layer, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile for flexible organic light-emitting diodes (OLEDs). This TCE demonstrates a high transmittance of about 81.34% at 550 nm and very low sheet resistance of 9.51 Ω sq −1 with excellent thermal stability under high-temperature (100 °C for 72 h) conditions. These properties arise from the synergistic effect of coordinate bonding between the nitrogen of the phenanthroline moiety and the Ag atom which leads to a smooth and uniform Ag surface and the o...

Ultrathin Ag Transparent Conducting Electrode Structure for Next-Generation Optoelectronic Applications

“…This result also shows that the multilayer Ag-TCE can be fabricated with a thinner Ag film and having electrical and optical properties comparable to the ITO electrode. It has been reported that the smooth surface topography of the ultrathin Ag film improves the transmittance by decreasing light scattering at the electrode surface . Also, this Ag-TCE showed better electrical and optical properties for the lower Ag thickness, as compared to the reported electrode structure .…”

“…The bottom HATCN layer prevents Ag agglomeration and forms uniform ultrathin Ag film by providing suitable nucleation sites for the Ag atoms, as shown in Figure S1. It has been reported that the organic wetting/nucleation layer supports to form a smooth ultrathin Ag film by preventing Ag agglomeration and forming coordinate bonds between Ag and nitrogen atoms through sharing unpaired electrons. , Typically, the ultrathin Ag film onto the organic layer can create an issue of Ag agglomeration under high temperature and device-operating conditions . Hence, the consecutive deposition of the capping layer (HATCN) onto the Ag film not only improves the transmittance of the TCE but also supports to stabilize the ultrathin Ag layer under different operating conditions by forming coordinate bonds between the nitrogen and Ag atoms (Figure S1).…”

Realizing Diketopyrrolopyrrole Polymer‐Based Uniform Large‐Area Transistors for Active Circuit via Protonic Acid Mediated Molecular Self‐Assembly

“…Au/Ag/HAT-CN configuration was developed to promote the effective hole injection from the drain electrode. [49] Finally, we successfully fabricated the PTFT-OLED active circuit based on blue emissive dyes. Figure 6 and Figure S33, Supporting Information, depicted the transfer curves and the corresponding optical images of the PTFT-OLED active circuit at a constant source-drain voltage of −50 V and the constant gate voltage of −50 V, which enable the PTFT to exhibit a switch-on state and supplied a current density of ≈0.625 mA cm −2 thus driving the OLED to achieve an electroluminescent brightness exceeding 100 cd cm −2 .…”

Metal‐Based Flexible Transparent Electrodes: Challenges and Recent Advances

“…These seeds provide dense nucleation centers for metal deposition, and suppress the growth of large metal islands during the PVD process. Such functional seeding materials include metals (Al, [40][41][42] Au, [43] Ag, [44] and Cu [45] ), dielectrics (Ta 2 O 5 , [46] ZnO, [47][48][49] NiO, [50] TeO 2 , [51] Nb 2 O 5 , [52] MoO 3 , [53] and Cs 2 CO 3 [54] ), polymers (polyethyleneimine [PEI], [19,[55][56][57][58] Ormoclear, [59] and photoresist SU-8 [60] ), and organic monolayers (11-mercaptoundecanoic acid [MUA], [48] [3-aminopropyl]-trimethoxysilane: [3mercaptopropyl]-trimethoxysilane [APTMS:MPTMS], [42,61,62] methyl-terminated alucone, [63] and 1,4-bis[2-phenyl-1,10-phenanthrolin-4-yl]benzene [p-bPPhenB] [64] ). For example, Schubert et al enhanced the wetting of deposited Ag films by using high surface energy metal seed materials such as Ca, Al, and Au (Figure 2a).…”