Printed Display Devices & Materials Junyou Pan TCL Corporate esearch
Motivation evaporated OLEDs Printed OLEDs in mass production Ease processing But only limited to medium size (up to Great deposition efficiency 6G, due to mask problem) Low production cost High production cost No need for mask ollable or flexible device Large area applications (8G or above) Various printing techniques available But performance should be improved Process should be defined 2
Printed OLED Approach I GB side-by-side (I) Cathode EIL ETL G B Interlayer (IL) buffer Anode evaporation solution evaporation (metal oxide) or solution (PEDOT) (II) Cathode evaporation G B IL solution buffer evaporation (metal oxide) Anode or Solution (PEDOT) Because of limited solution to stable soluble SM blue, this approach is mainly followed by polymer light emitting diodes (PLEDs) 3
Material Classes for PLEDs * * n Polyflourene * * n Phenanthrene * * n Benzofluorene * * n Dehydrophenanthrene Spiro bifluorene * * n Indenofluorene * * n All backbones are owned by few chemical companies
LEP Design ule for PLEDs ule: Function separation in polymer One unit one function Förster transfer Basic Backbone Unit m n N N o "Blue" Emitters p Blue Exciton generator Hole trap O B O O B O m n N N o "Green" Emitters p Green Exciton generator Hole trap "Blue" Emitters p m n N N o "Green" Emitters q White/ed Exciton generator Hole trap "ed" Emitters r e-transporting Backbone
Issues for PLEDs 1. Easy to print 2. Stable crosslinkable IL is required 3. Batch to batch variation (Mw, PD etc) must be reduced 4. Purification method should be developed: only the pure materiall is a good material 5. Overall synthesis cost is much higher than small molecules 6. Overall performance is lower than Evapored SM OLEDs
Printed OLED Approach II Hybrid Device I Cathode Cathode Cathode EIL EIL ETL Blue G IL buffer evaporation solution EIL ETL Blue G IL buffer HTL (SM) evaporation solution ETL Blue Hybrid Common G IL buffer Anode Anode Anode HTL (SM) No suitable common IL for blue Soluble SMHTL for blue HCL to avoid efficiency quenching in blue Hybrid approach is a feasiable and economical approch to printed SMOLED 7
Soluble SMs for Hybrid Device Critical issues: solubility, film formation, and amophous morphology Introduction of solubilizing groups (SLGs) to improve solubility & increase glass temperature without big change in electronic properties of the established materials system in evaporation system SLG1 Chemical lead structure evap. A. Hayer, et al., EL2012, 10-14 Dec. 2012 Hong Kong physics.hkbu.edu.hk/el2012hongkong/abstractsdownload/oral Session - Day 1/1A4.pdf Solubilising group can tune the critical parameters for soluble small molecular materials 8
State of the art Soluble Materials Du Pont Sourece: OLED World Summit 2014 Sourece: China International OLEDs Summit 2015, Shanghai Merck: achieved soluble red and green material sets comparable to evaporated materials 9
Soluble SM Issues 1. So far, excellent SLGs for green and red triplet were successfully developed eloped for solution-process. 2. Suitable SLG for bule is elusive. 3. Photooxidation is a problem for triplet green and red emitters. 4. Solution-processed SM HTM for high performance blue is still missing. Cathode EIL ETL Blue Hybrid Common G HTL IL (SM) buffer Anode 5. Printability should be proved. 10
Printed OLED Approach III Hybrid Device II (New) Latest Progress in QD-LED Paul H. Holloway, et al., IDW 14, 1250 Peng et al., Nature vol 515, 96 (2014): New Device Structure: with electron blocking layer on cathode side EQE of 20.5% Sub-bandgap turn-on at 1.7V Long lifetime > 100k hours @ 100nits QD-LED: A field moving quickly forward 11
Printed OLED Approach III Hybrid Device II (New) Cathode EIL ETL G QDB HTL buffer Anode Or Cathode EIL ETL QD G QDB HTL buffer Anode Evaporation or solution solution evaporation (metal oxide) or solution (PEDOT) Advatages: 1. High performance of SM OLED G and / or 2. Narrow emission band high color gamut 3. QD less sensitive to air A combination of advatages of soluble SM and QD A promising technology for all printed display 12
OLED 印刷工艺技术
印刷技术的选择 INK-JET 喷墨印刷 EPSON: 360 dpi, 600dpi ongoing Nozzle 喷嘴印刷 DuPont: < 250dpi 工艺精度与 产量的平衡 凸 / 凹版印刷 ( 非主流 ) Sony
国外印刷 OLED 样机 Panasonic International CES 2013 AUO SID 2014 Display Week 56 英寸 4K2K 印刷 OLED 显示 65 英寸 1920 1080 印刷 OLED 显示
国内印刷 OLED 样机 京东方 喷墨印刷 AM-OLED TCL/ 华星光电 喷墨印刷 AM-OLED 30 英寸 / 金属氧化物 TFT / FHD 31 英寸 / 金属氧化物 TFT / FHD
印刷工艺面临的问题 咖啡环效应 挥发速率由中心向外逐渐变大 不同尺寸墨滴干燥后形成的咖啡环现象, 边缘高度明显大于内部 浓度差导致墨滴内溶液由内向外补充, 干燥后外厚内薄 Mura 现象 由于印刷的均匀性引 起的显示明暗条纹
印刷工艺面临的问题 像素内均匀性 ---- Coffee ing Free 基板 /INK 表面能态匹配 表面处理与 INK 的匹配 大面积均匀性 ---- Mura Free 多喷头平均化技术 ---- 消除喷头打印墨滴体积的个体差异 多波形的喷头驱动技术 ---- 实现不同体积的打印墨滴 墨滴测量技术 ---- 快速检测墨滴的体积或重量 优化打印控制算法 ---- 通过实检测墨滴的数据来控制墨滴喷印方案
印刷工艺面临的问题 打印精度的进一步提高 > 400 PPI 关键问题 : 墨滴的扩散控制 A. G. Yodh et al., Nature, 2011,476, 308
Summary 1. Polymers good solubility, printability and film formation properties p High synthesis cost purity and reliability problem 2. Soluble small molecules Material technology for G & established, already close to commercialisation Material set of HTL and EML for blue to be improved Stability issue in air 3. Quantum Dots High performamce blue elussive Printability should be addressed
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