含1,1-二(4-(N,N-二甲基胺基)苯基)-2,3,4,5-四苯基噻咯的聚合物在三种阴极结构中的电致发光性能

Electroluminescence performances of 1,1-bis(4-(N,N-dimethylamino)phenyl)-2,3,4,5-tetraphenylsilole based polymers in three cathode architectures

设计合成了一种1,1-位为二(4-(N,N-二甲基胺基)苯基的新型噻咯单体,并与2,7-芴单体聚合得到六苯基噻咯单体投料量为1%、10%、20%的三种共聚物PF-N-HPS1～20.研究了这些共聚物的紫外吸收光谱、电化学性质、光致发光光谱和电致发光性能.PF-N-HPS的HOMO能级为5.25～5.58eV,呈现绿光发射.以PF-N-HPS为发光层,制作了三种聚合物发光二极管(器件结构A:ITO/PEDOT/PF-N-HPS/Al;器件结构B:ITO/PEDOT/PF-N-HPS/Ba/Al;器件结构C:ITO/PEDOT/PF-N-HPS/TPBI/Ba/Al).其中器件结构A的电致发光效率仅为0.1～0.33cd/A,说明PF-N-HPS中的4-(N,N-二甲基胺基)苯基结构不能使单独的Al阴极实现良好的电子注入.采用了低功函金属Ba阴极的器件结构B能改善电子的注入,使电致发光效率提高到0.85～1.44cd/A.器件结构C采用TPBI(HOMO:6.2eV)作为电子传输和空穴阻挡层,促进了电子和空穴的有效复合,进一步提高了电致发光效率(4.56～7.96cd/A),其中TPBI层将噻咯聚合物与金属阴极隔离可能减少发光层在阴极界面处的激子猝灭也起到了一定的作用,器件结构C较器件结构B还获得了更好的绿光光谱.

A new silole monomer with two 4-（N,N-dimethylamino）phenyl substitutions on silicon atom was designed and synthesized. Three copolymers PF-N-HPS1, PF-N-HPS10 and PF-N-HPS20 were then obtained by copolymerizations of 2,7-fluorene derivatives with the silole monomer at feed ratios of 1%, 10%, and 20%. Their UV-vis absorption, electrochemical, photoluminescent, and electroluminescent （EL） properties were investigated. PF-N-HPS possessed HOMO levels of-5.25--5.58 eV, and showed green emissions. Using PF-N-HPS as the emissive layer, three different polymer light-emitting diodes were fabricated as device A with ITO/PEDOT/PF- N-HPS/A1, device B with ITO/PEDOT/PF-N-HPS/Ba/A1, and device C with ITO/PEDOT/PF-N-HPS/TPBI/Ba/A1. For the device A, PF-N-HPS only showed very low EL efficiency of 0.1-0.33 cd/A, indicating that the A1 cathode could not inject electron efficiently to the emissive polymers containing the 4-（N,N-dimethylamino）phenyl groups. For the device B, low work function Ba supplied better electron injections, and the EL efficiency could be improved to 0.85-1.44 cd/A. TPBI with a deep HOMO level of -6.2 eV could enhance electron transport and hole blocking. Thus modified recombinations and largely elevated EL efficiency of 4.56-7.96 cd/A were achieved for the device C. The separation of the emissive layer and metal cathode with the TPBI layer may also suppress exciton quenching at the cathode interface.