TADF激基复合物主体材料提升溶液法制备蓝色荧光有机发光二极管的效率

为了提升溶液法制备的蓝色荧光有机发光二极管(OLEDs)的效率,采用了基于热激活延迟发光(TADF)的激基复合物作为主体材料。TADF激基复合物主体可以利用反向系间窜跃上转换形成单线态激子并将能量传递到客体,从而可以同时利用发光层中的三线态激子和单线态激子,以提升蓝色荧光器件的效率。选择蓝色荧光材料1-4-Di-[4-(N,N-diphenyl)amino]styryl-benzene(DSA-ph)作为客体发光材料,4,4′,4″-T-ris(carbazol-9-yl)triphenylamine(TCTA)掺杂1,3,5-Tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)(TPBi)作为热激活延迟荧光激基复合物主体,通过溶液法制备了蓝色荧光OLEDs。通过测试TCTA,TPBi以及TCTA掺杂TPBi的光致发光光谱发现,与TCTA和TPBi相比,TCTA掺杂TPBi的光致发光谱(PL)发生了明显的红移(峰值波长变为437 nm),而且光谱变宽,证明了TCTA∶TPBi激基复合物的形成。通过对于DSA-ph掺杂激基复合物主体的薄膜与DSA-ph掺杂poly(methyl methacrylate)(PMMA)的薄膜进行PL测试发现,两者发光峰相同,都是来自DSA-ph的发光,说明激基复合物主体将能量传递到了DSA-ph;DSA-ph的吸收光谱与激基复合物主体的PL光谱存在很大重叠,说明激基复合物主体与DSA-ph的能量传递非常有效;通过对激基复合物主体掺杂不同浓度客体的薄膜进行瞬态PL衰减测试发现,与纯DSA-ph的寿命相比,DSA-ph掺杂激基复合物主体之后其寿命会延长,纯DSA-ph的寿命只有1.19 ns,DSA-ph掺杂激基复合物主体的荧光衰减曲线与激基复合物主体的荧光衰减曲线相似,这进一步证明了激基复合物主体将能量传递到了DSA-ph。研究了主体引入以及DSA-ph掺杂浓度对器件性能的影响。对于器件的亮度、电流密度、电压、电流效率、电致发光光谱等参数进行了测试,与不采用激基复合物主体的器件相比,采用激基复合物主体的器件性能明显改善,在DSA-ph掺杂浓度为10%时,器件亮度从2133.6 cd·m^-2提升到了3597.6 cd·m^-2,器件效率从1.44 cd·A-1提升到了3.15 cd·A-1,发光峰只有来自DSA-ph的发光。采用TADF激基复合物主体的方法有潜力实现溶液法制备的高效蓝色荧光OLEDs。

Improving the Efficiency of Solution-Processed,Blue Fluorescent Organic Light-Emitting Diodes(OLEDs) by Employing TADF Exciplex Hosts

In order to improve the efficiency of solution-processed,blue fluorescent organic light emitting diodes(OLEDs),we propose the use of exciplex hosts with thermal-activated delayed fluorescence(TADF).The TADF exciplex hosts can utilize upconverted singlet excitons by reverse intersystem crossing and then transfer the energy to the guest to improve efficiency of the blue fluorescent OLEDs,which enables the full utilization of triplet and singlet excitons.Here,blue fluorescent material 1-4-Di-[4-(N,N-diphenyl)amino]styryl-benzene(DSA-ph)issued as the guest emitting material,4,4’,4’’-Tris(arbazol-9-yl)t-riphenylamine(TCTA)doped 1,3,5-Tri(1-phenyl-1 H-cbenzo[d]imidazol-2-yl)phenyl)(TPBi)was used as the TADF exciplex hosts,and the emitting layer was fabricated by solution process.From the photoluminescence(PL)spectra of TCBi,TPBi and TCTA doped TPBi films,it was found that the emission peak of TCTA doped TPBi film was significantly red-shifted compared to that of pristine TCTA or TPBi films(peak wavelength changes to 437 nm).Meanwhile,the spectrum broadens,which proves the existence of exciplex.The PL spectra of DSA-ph doped exciplex hosts and DSA-ph doped poly(methyl methacrylate)(PMMA)films were found to be the same and both of the photol-uminescence peaks were derived from DSA-ph,which proved that exciplex hosts transfer energy to DSA-ph.The absorption spectrum of DSA-ph overlaped greatly with the PL spectrum of exciplex hosts,which also proved that the exciplex hosts transfer energy to DSA-ph effectively.Time-resolved PL measurements were performed on exciplex hosts doped with different concent-rations of the DSA-ph guest.It was found that the lifetime of the DSA-ph doped exciplex hosts becomes longer compared to that of the pure DSA-ph.The lifetime of pure DSA-ph is only 1.19 ns.The fluorescence decay curve of DSA-ph doped exciplex hosts is similar to that of exciplex hosts,which further demonstrates that the exciplex hosts transfer energy to the DSA-ph.We investigated the effects of the presence of TADF exciplex hosts and the DSA-ph con-centration on the device performance.The parameters such as brightness,current density,voltage,current efficiency,electroluminescence spectra of the devices were measured.The perfor-mance of the OLEDs using exciplex hosts were notably improved,compared to standard OLE-Ds without exciplex hosts.In the condition of 10%DSA-ph,the luminescence increased from 2133.6 cd·m^-2(for pristine DSA-ph)to 3597.6 cd·m^-2,and the current efficiency increased from 1.44 cd·A-1(for pristine DSA-ph)to 3.15 cd·A-1.All of the electroluminescence peaks were only derived from DSA-ph.The concept of using TADF exciplex hosts provided a facile way to achieve high performance solution-processed blue fluorescent OLEDs.