Study On High-efficiency And High-stability Organic Light-emitting Devices

Organic light-emitting diodes(OLEDs)have attracted attention worldwide as a promising technology for use in full-color display and indoor lighting,due to their superior merits,such as flexibility,lightweight and health.In this paper,we primarily focus on high efficiency and high operational stability OLEDs,from the aspects of the interfacial engineering between electrode and organic layer,design and synthesis of novel bipolar spiro-materials,device architecture of high efficiency OLEDs with extremely low operating voltage,device fabrication of high performance mono-chromatic and white OLEDs with high power efficiency at high brightness,and light manipulation for white emission.The investigation is summarized in the following sections:In Section 1,we employed an organic molecule HAT-CN as a“scavenging layer”on clean and contaminated ITO electrodes.Besides the improvement of hole-injection,HAT-CN could dramatically improve the electroluminescence of OLEDs.Furthermore,owing to the modification layer,the contamination above the electrodes will not have negative effects on the corresponding device performance,such as current or power efficiency,and operational lifetime.Therefore,this convenient modification method could be universally applied in the optoelectronic devices.In Section 2,we synthesized two novel D-Spiro-A based bipolar spiro-materials,STPy3 and STPy4,with high triplet energy level.They could act as“universal hosts”for high efficiency red,green,blue and even white OLEDs,whose highest EQE were all over20%.Especially for STPy4 based white OLED,its highest EQE can be reached up to27.8%,and its efficiency roll-off at 1000 cd/m~2 can be as low as 1.0%.In Section 3,in order to realize low driving voltage,we utilized STPy3/4 as donors,and selected PO-T2 T as an acceptor for an exciplex induced co-host system.As a result,the corresponding green and yellow OLEDs achieve extremely low turn-on voltage of 2.1V,and the highest power efficiency of green ones was over 140.0 lm/W.In Section 4,for highly efficient WOLEDs hosted by exciplex with low triplet energy level,we put forward a new strategy called the allocation of gradient exciplex(AGE)to rationally manipulate the excitons and adjust the recombination zone to realize the white emission.Thus,STPy3/4 and AGE based white OLEDs incorporated the extremely low turn-on voltage of 2.3 V,which was the lowest value ever reported.Moreover,the highest EQE was 28.2%,and the power efficiency at 1000 cd/m~2 boosted to 72.7 lm/W,which has outperformed that of fluorescent tubes.In Section 5,nano-imprinting method was used to transfer the spontaneously formed quasi-random corrugations into the PEDOT:PSS layer in OLEDs.The nano-patterned OLEDs could out-couple the wide band of emission spectrum.For yellow phosphorescent OLEDs,the highest EQE of the nano-patterned ones was over 30%,nearly 1.76 enhancement of yellow OLEDs with planar structures.Combined with exciplex,the nano-patterned ones of blue OLEDs owned the highest EQE beyond 35.3%,which was also 1.75 enhancement to the planar ones.In summary,this paper provided a systematic investigation of the interfacial engineering,molecular design,materials synthesis,light manipulation,and device architecture and fabrication.All of them can make contributions to the development of high-efficiency and high-stability OLEDs.