Optimization of High-Performance Blue Organic Light-Emitting Diodes Containing Tetraphenylsilane Molecular Glass Materials

Abstract

Molecular glass material (4-(5-(4-(diphenylamino)phenyl)-2-oxadiazolyl)phenyl)triphenylsilane (Ph(3)Si(PhTPAOXD)) was used as the blue light-emitting material in the fabrication of high-performance organic light-emitting diodes (OLEDs). In the optimization of performance, five types of OLEDs were constructed from Ph(3)Si(PhTPAOXD): device I, ITO/NPB/Ph(3)Si(PhTPAOXD)/Alq(3)/Mg:Ag, where NPB and Alq(3) are 1,4-bis(1-naphylphenylamino)biphenyl and tris(8-hydroxyquinoline)aluminum, respectively; device II, ITO/NPB/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag, where TPBI is 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene; device III, ITO/Ph(2)Si(Ph(NPA)(2))(2)/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag, where Ph(2)Si(Ph(NPA)(2))(2) is bis(3,5-bis(1-naphylphenylamino)phenyl)-diphenylsilane, a newly synthesized tetraphenylsilane-containing triarylamine as hole-transporting material; device IV, ITO/Ph(2)Si(Ph(NPA)(2))(2)/NPB/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag; device V, ITO/CuPc/NPB /Ph(3)Si(PhTPAOXD)/Alq(3)/LiF/Al, where CuPc is Cu(II) phthalocyanine. Device performances, including blue color purity, electroluminescence (EL) intensity, current density, and efficiency, vary drastically by changing the device thickness (100-600 A of the light-emitting layer) and materials for hole-transporting layer (NPB and/or Ph(2)Si(Ph(NPA)(2))(2)) or electron-transporting material (Alq(3) or TPBI). One of the superior OLEDs is device IV, showing maximum EL near 19 000 cd/m(2) with relatively low current density of 674 mA/cm(2) (or near 3000 cd/m(2) at 100 mA/cm(2)) and high external quantum efficiency of 2.4% (1.1 lm/W or 3.1 cd/A). The device possesses good blue color purity with EL emission maximum (lambda(max)(EL)) at 460 nm, corresponding to (0.16, 0.18) of blue color chromaticity on CIE coordinates. In addition, the device is reasonably stable and sustains heating over 100 degrees C with no loss of luminance on the basis of the annealing data for device V. Formation of the exciplex at the interface of NPB and Ph(3)Si(PhTPAOXD) layers is verified by EL and photoluminescence (PL) spectra studies on the devices with a combination of different charge transporting materials. The EL due to the exciplex (lambda(max)(EL) at 490-510 nm) can be properly avoided by using a 200 A layer of Ph(3)Si(PhTPAOXD) in device I, which limits the charge-recombination zone away from the interface area.

New Trends in the Use of Transition Metal–Ligand Complexes for Applications in Electroluminescent Devices

“…Usually bathocuproine (BCP) [13,19,22,48,49] and (biphenyloxolatoaluminum(III) bis[2-methylquinolinato(phenylphenolate)] (BAlq) [65,73] are used as HBL or exciton-blocking layers. Other compounds, such as fluorinated phenylenes [51] and oxadiazole, as well as triazolecontaining molecules such as the trimer of N-arylbenzimidazoles (TPBi), [74,75] 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD), [24] 3-phenyl-4-(1¢-naphthyl)-5-phenyl-1,2,4-triazole (TAZ), [76,77] 1,8-naphthalimides, [78] polyquinolines, [79] or carbon nanotubes doped in PPV [80] were also found to be useful as HBLs. In the last step, depositing a cathode completes the assembly of the device.…”

New Dopant and Host Materials for Blue‐Light‐Emitting Phosphorescent Organic Electroluminescent Devices

“…The synthesis of the new host material SimCP was successfully performed by the Pd-catalyzed (Pd[OAc] 2 , P[tBu] 3 , and K 2 CO 3 in xylenes, where Ac = acetyl and tBu = t-butyl) aromatic amination reaction of 3,5-dibromo-tetraphenylsilane with carbazole. 3,5-Dibromotetraphenylsilane was synthesized in our laboratory by a modified literature procedure for the synthesis of 3,5,3¢,5¢-tetrabromotetraphenylsilane [40]. N,N¢-di(naphthalene-1-yl)-N,N¢-diphenylbenzidine (NPB) and 2,2¢,2²-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole) (TPBI) were adopted in device fabrication as the hole-transporting and hole-blocking/electron-transporting layers, respectively.…”

Efficient Organic Blue‐Light‐Emitting Devices with Double Confinement on Terfluorenes with Ambipolar Carrier Transport Properties

“…As an instance, employing the widely used electron-transport material Alq 3 as the ETL for blue OLEDs often leads to partial emission from Alq 3 and thus deterioration of color purity of blue EL, mainly due to lack of effective exciton and carrier confinement. [9,31] In this work, the double-heterostructure configuration with effective confinement on both types of carriers and excitons has for the first time been successfully implemented in blue OLEDs through judicious choice and combination of materials. An issue that has long been of interest with fluorene-based blue emitters is the emergence of red-shifted emission bands and consequently degraded color purity associated with morphological variation or oxidative degradation of materials during annealing or passage of current.…”