Highly Efficient Near Ultraviolet Organic Light-emitting Device Based on WCl₆ Doped PEDOT∶PSS as Hole Injection Layer Enhanced Publication

WCl 6 掺杂PEDOT∶PSS作为空穴注入层的高效率近紫外有机发光器件 Highly Efficient Near Ultraviolet Organic Light-emitting Device Based on WCl 6 Doped PEDOT∶PSS as Hole Injection Layer 1 first-author 王家兴(1997-)，男，安徽宿州人，硕士研究生，2019年于安徽理工大学获得学士学位，主要从事紫外有机发光器件的研究。E-mail: 2741882146@qq.com http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=22919112&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=22919117&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=22919122&type= 王家兴 (1997-)，男，安徽宿州人，硕士研究生，2019年于安徽理工大学获得学士学位，主要从事紫外有机发光器件的研究。E-mail: 2741882146@qq.com 2741882146@qq.com 1 1 1 2 3 3 1 corresp E-mail: zhang-xiaowen@163.com E-mail: zhang-xiaowen@163.com 张小文(1977-)，男，湖南邵阳人，博士，教授，2010年于上海大学获得博士学位，主要从事有机发光材料与器件、量子点器件的研究。E-mail: zhang-xiaowen@163.com http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=22919126&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=22919131&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=22919136&type= 张小文 (1977-)，男，湖南邵阳人，博士，教授，2010年于上海大学获得博士学位，主要从事有机发光材料与器件、量子点器件的研究。E-mail: zhang-xiaowen@163.com zhang-xiaowen@163.com 桂林电子科技大学　广西电子信息材料构效关系重点实验室，广西　桂林　541004 桂林电子科技大学　广西电子信息材料构效关系重点实验室，广西　桂林　541004 Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, China Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, China 电子科技大学中山学院　电子薄膜与集成器件国家重点实验室中山分室，广东　中山　528402 电子科技大学中山学院　电子薄膜与集成器件国家重点实验室中山分室，广东　中山　528402 Zhongshan Branch of State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Zhongshan Institute, Zhongshan 528402, China Zhongshan Branch of State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Zhongshan Institute, Zhongshan 528402, China 中国有色桂林矿产地质研究院有限公司　广西超硬材料重点实验室，　桂林市微电子元件电极材料与生物纳米材料重点实验室，广西　桂林　541004 中国有色桂林矿产地质研究院有限公司　广西超硬材料重点实验室，　桂林市微电子元件电极材料与生物纳米材料重点实验室，广西　桂林　541004 Guilin Key Laboratory of Microelectronic Electrode Materials and Biological Nanomaterials, Guangxi Key Laboratory of Superhard Materials, China Monferrous Metal (Guilin) Geology and Mining Co., Ltd., Guilin 541004, China Guilin Key Laboratory of Microelectronic Electrode Materials and Biological Nanomaterials, Guangxi Key Laboratory of Superhard Materials, China Monferrous Metal (Guilin) Geology and Mining Co., Ltd., Guilin 541004, China 紫外有机发光器件(OLED)的宽带隙发光分子限制了空穴注入效率，从而导致载流子复合低效，器件发展受限。可溶液处理工艺兼顾了低成本、高可控性及规模生产的时代特色。本文报道了利用溶液法制备的WCl 6 及其与聚(3,4-乙烯二氧噻吩)-聚苯乙烯磺酸掺杂复合物(PEDOT∶PSS+WCl 6 )调控近紫外OLED的空穴注入特性，实现了高效率近紫外有机发光。X射线光电子能谱、紫外-可见光吸收光谱等分析表明，WCl 6 和PEDOT∶PSS+WCl 6 薄膜具有优异的电子特性和光透过性。伏安特性和阻抗谱分析表明，空穴注入能力按WCl 6 、PEDOT∶PSS和PEDOT∶PSS+WCl 6 的顺序依次增强。以PEDOT∶PSS+WCl 6 作空穴注入层、2-(4-联苯)-5-(4-叔丁基苯基)-1,3,4-恶二唑(PBD)作发光层，获得了最大外量子效率为2.6%、最大辐照度为8.05 mW/cm 2 、半峰宽为45 nm、电致发光峰为405 nm的高效率近紫外OLED。器件寿命测试对比结果表明，WCl 6 掺杂PEDOT∶PSS后器件的稳定性得到了增强。 该研究结果拓展了WCl 6 的应用领域，对于推进高效稳定近紫外OLED的进一步发展具有一定的借鉴意义。 Wide bandgap of emissive molecule in ultraviolet organic light-emitting device(UV-OLED) restricts hole injection, which results in inefficient carrier recombination and counteracts performance promotion. Solution-processed techniques with low cost, fine tunability and high throughout production meet the current requirement of manufacture. Herein, solution-processed WCl 6 and its doping composite of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT∶PSS)+WCl 6 are employed for tailoring hole injection of near UV-OLED, and thus achieving high efficiency. X-ray photoelectron spectroscopy and UV-visible absorption analysis show that WCl 6 and PEDOT∶PSS+WCl 6 films behave exceptional electronic properties and superior optical transmittance. Current-voltage characteristics and impedance spectroscopy analysis confirm that the hole injection ability is enhanced in the order of WCl 6 , PEDOT∶PSS and PEDOT∶PSS+WCl 6 . Using PEDOT∶PSS+WCl 6 as hole injection tailoring and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(PBD) as emissive layer, the near UV-OLED reaches maximum external quantum efficiency of 2.6%, radiance of 8.05 mW/cm 2 , full width at half maximum of 45 nm and electroluminescent peak of 405 nm. Device aging tests indicate that WCl 6 doped PEDOT∶PSS considerably enhances the stability of near UV-OLED. Our results expand the application of WCl 6 and efficient stable near UV-OLED. 紫外有机发光器件 WCl 6 可溶液加工 空穴注入 阻抗谱 ultraviolet organic light-emitting device WCl 6 solution process hole injection impedance spectroscopy 引言 1 有机电致发光器件(OLED)因其高亮度、均匀自发光、轻便柔性以及广色域显示等特点，在激发光源、化学传感器、存储器和医疗领域有着广泛的应用 [ 1 1 - 2 2 1-2 ] 。相比于已经量产的可见光OLED，近紫外有机电致发光器件(NUV-OLED)因有机发光分子带隙宽导致的载流子注入条件苛刻、发光效率低、老化速度快以及成本偏高等缺点阻滞了其实用化进程 [ 2 2 - 3 3 2-3 ] 。在已然成熟的OLED阳极氧化铟锡(ITO)、反射阴极Al的架构上，NUV-OLED的载流子注入调控面临更艰难的技术壁垒。因此，探索高效、能级适中的空穴注入层(HIL)是发展高性能器件的重要一环。利用溶液法制备低成本HIL，置于电极与发光层之间，组成多层结构使载流子实现梯度注入，改善了器件效率及使用寿命。发展至今，基于传统荧光分子发光的紫外OLED的外量子效率(EQE)达到4.6% [ 4 4 ] 。通过器件老化机制，EQE提升到8.2% [ 5 5 ] 。基于新型热激活延迟荧光发光分子的紫外OLED将EQE提升至9.3% [ 6 6 ] 。溶液法还可精准调控HIL的厚度以及组分掺杂比例，在低成本、大规模量产方面大显身手。目前研究较多的HIL包括开发过渡金属化合物或二维材料(WO x [ 7 7 ] ,MoO x [ 8 8 ] ,VO x [ 9 9 ] ,MoS 2 [ 10 10 - 11 11 10-11 ] ,WS 2 [ 11 11 - 12 12 11-12 ] ,TaS 2 [ 11 11 ] ,GO [ 13 13 ] ,C 3 N 4 [ 14 14 ] )，使用多层涂覆叠加或p型掺杂复合层(如:聚(3,4-乙烯二氧噻吩)-聚苯乙烯磺酸(PEDOT∶PSS)/MoO x [ 4 4 ] ,MoO x +PEDOT∶PSS [ 15 15 ] ,MoS 2 +PEDOT∶PSS [ 10 10 ] ,WS 2 +PEDOT∶PSS [ 12 12 ] )进行优化。WCl 6 具有优良的溶解度和导电性，且W元素具有W 4+ 、W 5+ 、W 6+ 等多种化学价态，可以充当优异的p型掺杂客体，增强空穴的转移能力，从而具有较好的界面电荷转移特性，在化工材料和医药领域有广泛的应用；WCl 6 也是常用的聚合催化剂和氧化偶联剂 [ 16 16 ] ;WCl 6 作为调控功能层在太阳能电池和半导体器件中有着优秀的载流子调节作用 [ 17 17 - 18 18 17-18 ] 。本文详细研究了溶液法制备的WCl 6 及其复合掺杂薄膜(PEDOT∶PSS+WCl 6 )在高效NUV-OLED中的空穴注入调控作用。以2-(4-联苯)-5-(4-叔丁基苯基)-1,3,4-恶二唑(PBD)荧光分子为发光层、PEDOT∶PSS+WCl 6 为HIL的NUV-OLED的最大EQE达到了2.6%，最大发光强度为8.05 mW/cm 2 ，电致发光(EL)峰位于405 nm处，半峰宽(FWHM)为45 nm。该性能也是目前基于PBD近紫外有机发光的较优值。该研究结果促进了高效NUV-OLED的发展，也拓宽了金属氯化物的应用范围。 实验 1 前驱体溶液合成 2 将WCl 6 粉末( > 99.9%,Acros organics)溶于无水乙醇中。在大气环境中，100 r/min转速下，常温搅拌30 s，搅拌溶解均匀得到浅黄色的WCl 6 乙醇溶液(如 图1 图1 所示)。将所得溶液放入干燥N 2 手套箱中保存备用。 器件制备 2 ITO玻璃经常规化学清洗、紫外光-臭氧照射后，将WCl 6 乙醇溶液、PEDOT∶PSS(AI-4083,Heraeus)或PEDOT∶PSS+WCl 6 旋涂在ITO阳极上，在空气中退火后获得相应的HIL。继而在真空为10 -4 Pa的蒸镀室中沉积4,4'-二(9-咔唑)联苯(CBP)、PBD、4,7-二苯基-1,10-菲啰啉(BPhen)等有机功能层，分别作为空穴传输层(HTL)、发光层(EML)和电子传输层(ETL)。器件有源发光面积为5 mm×5 mm，器件结构、能级匹配及有机分子结构如 图1 图1 所示。为了研究不同的HIL对器件光电性能的影响，设计了一系列NUV-OLED器件，如下所示: 器件W1:ITO/WCl 6 (0.2 mg/mL)/CBP(30 nm)/PBD(35 nm)/BPhen(110 nm)/LiF(2 nm)/Al(100 nm); 器件W2:ITO/WCl 6 (0.5 mg/mL)/CBP/PBD/BPhen/LiF/Al; 器件W3:ITO/WCl 6 (1 mg/mL)/CBP/PBD/BPhen/LiF/Al; 器件W4:ITO/WCl 6 (3 mg/mL)/CBP/PBD/BPhen/LiF/Al; 器件P:ITO/PEDOT∶PSS/CBP/PBD/BPhen/LiF/Al; 器件PC:ITO/PEDOT∶PSS+C 2 H 5 OH(1∶1)/CBP/PBD/BPhen/LiF/Al; 器件PW1:ITO/PEDOT∶PSS+WCl 6 (1∶2)/CBP/PBD/BPhen/LiF/Al; 器件PW2:ITO/PEDOT∶PSS+WCl 6 (1∶1)/CBP/PBD/BPhen/LiF/Al; 器件PW3:ITO/PEDOT∶PSS+WCl 6 (3∶1)/CBP/PBD/BPhen/LiF/Al; 器件PW4:ITO/PEDOT∶PSS+WCl 6 (5∶1)/CBP/PBD/BPhen/LiF/Al。 性能表征 2 用X射线光电子能谱(XPS)分析元素种类和价态。用PerkinElmer Lambda 365紫外-可见分光光度计测定紫外-可见光吸收光谱。用Keithley 2400源表和海洋光学Maya2000Pro光谱扫描计测试电流密度( J )、电压( V )、发光强度( R )和EL光谱。用Agilent 4294A阻抗仪测量单空穴器件(HOC)的阻抗-电压( Z-V )、相角-电压( Φ-V )和电容-电压( C-V )转变曲线。 结果与讨论 1 WCl 6 与PEDOT∶PSS+WCl 6 薄膜的W、C和O元素的XPS分析如 图2 图2 所示。 图2(a)~(b) 图2(a)~(b) 是WCl 6 与PEDOT∶PSS+WCl 6 薄膜的W4f谱，W元素存在W 5+ 和W 6+ 两种价态，且W4f分裂为W4f 7/2 和W4f 5/2 轨道。W 5+ 的特征峰对应在结合能~35.6 eV和~37.8 eV处，W 6+ 的特征峰对应在结合能~36.2 eV和~38.4 eV处。从图中可以看出WCl 6 与PEDOT∶PSS+WCl 6 退火后，都出现了W 5+ 信号，表明WCl 6 向WO x ( x < 3)转化，即部分W 6+ 在退火后价态发生转变。在掺杂的复合薄膜中，PEDOT∶PSS的酸性(H + )还会进一步将部分W 6+ 还原成为W 5+ ，故PEDOT∶PSS+WCl 6 薄膜中W 5+ 所占比例更大 [ 8 8 ] 。 图2(c)、(d) 图2(c)、(d) 显示了WCl 6 与PEDOT∶PSS+WCl 6 薄膜中C元素的精细谱。C1s除了在结合能~284.8 eV显示谱峰外，在~286.2 eV处还有一个肩峰，对应于C—O键 [ 19 19 ] 。 图2(e)~(f) 图2(e)~(f) 表示的是O1s谱。WCl 6 与PEDOT∶PSS+WCl 6 有两个相同谱峰，位于~530.8 eV对应的是WO 3 中的氧离子，而位于~532.2 eV对应的是吸附氧 [ 14 14 ] 。进一步分析还可以看出，WCl 6 中位于~530.8 eV谱峰的信号强度明显增加，表明WCl 6 的表面更容易氧化形成WO 3 ，而WCl 6 掺杂在PEDOT∶PSS中，暴露在样品表面的W元素含量较少，因此掺杂体中的WO 3 含量更少。此外，在PEDOT∶PSS+WCl 6 中还存在一个位于~533.6 eV的肩峰，这是来源于PEDOT∶PSS长链中的氧 [ 19 19 ] 。 各HIL对应的NUV-OLED的光电性能总结在 表1 表1 中，对应的 J-V-R 和EL谱如 图3 图3 所示。对比可以看出，当WCl 6 溶液为0.5 mg/mL、80 ℃退火处理成膜后，器件(W2)获得了较好的性能，EQE值为1.8%@9.71 mA/cm 2 ，辐照度为6.19 mW/cm 2 @15.5 V，优于其他浓度WCl 6 作HIL的器件。PEDOT∶PSS与乙醇共掺(器件PC)对器件性能稍有改善，但效果并不明显，故排除乙醇溶剂的影响。在以PEDOT∶PSS+WCl 6 作为HIL时，WCl 6 溶液的浓度选定为0.5 mg/mL。进一步通过优化掺杂比例提高器件性能。实验结果表明，当掺杂比例PEDOT∶PSS+WCl 6 =3∶1时，器件具有最大EQE值2.60%@5.81 mA/cm 2 ，比WCl 6 (器件W2,1.8%)和PEDOT∶PSS(器件P,1.88%)作HIL的NUV-OLED分别提高了44.4%和38.3%，略优于WO x +PEDOT∶PSS(对应器件最大EQE为2.3% [ 20 20 ] )、WS 2 +PEDOT∶PSS(对应器件最大EQE为2.1% [ 12 12 ] )和Li 2 CO 3 (对应器件最大EQE为2.4% [ 21 21 ] )调控载流子注入特性的NUV-OLED器件。这也是目前报道的基于PBD做发光层、ITO做透明阳极这一结构NUV-OLED器件的最高效率值。基于PEDOT∶PSS+WCl 6 =3∶1调控空穴注入的NUV-OLED的最大辐照度达到了8.05 mW/cm 2 @14.5 V,EL峰位于405 nm,FWHM为45 nm。 图3(d) 图3(d) 是不同HIL器件的EL光谱，各器件的主发光峰位于403~405 nm处，来自于有机分子PBD的近紫外发射。EL谱中观察到的微弱肩峰以及光谱形状和半峰宽等细微差别，主要是来自界面激基复合物甚至毗邻的有机功能层发光所致。 1 1 器件编号 1 1 HIL 1 1 退火温度/℃ 1 1 最大EQE/ 1 1 最大辐照度/(mW·cm -2 ) 1 1 EL峰/nm 1 1 FWHM/nm 1 1 W1 1 1 WCl 6 (0.2 mg/mL) 1 1 80 1 1 1.55%@ 6.93 mA/cm 2 1 1 3.8@16 V 1 1 405 1 1 54 1 1 W2 1 1 WCl 6 (0.5 mg/mL) 1 1 80 1 1 1.8%@9.71 mA/cm 2 1 1 6.19@15.5 V 1 1 404 1 1 54 1 1 W3 1 1 WCl 6 (1 mg/mL) 1 1 80 1 1 1.76%@6.51 mA/cm 2 1 1 6.0@15.5 V 1 1 401 1 1 58 1 1 W4 1 1 WCl 6 (3 mg/mL) 1 1 80 1 1 1.5%@ 41.43 mA/cm 2 1 1 5.4@15.5 V 1 1 405 1 1 54 1 1 P 1 1 PEDOT∶PSS 1 1 120 1 1 1.88%@ 1.1 mA/cm 2 1 1 2.02@13.5 V 1 1 403 1 1 49 1 1 PC 1 1 PEDOT∶PSS+C 2 H 5 OH=1∶1 1 1 120 1 1 2.02%@ 1.07 mA/cm 2 1 1 4.87@13 V 1 1 403 1 1 49 1 1 PW1 1 1 PEDOT∶PSS+WCl 6 =1∶2 1 1 100 1 1 2.21%@ 3.38 mA/cm 2 1 1 6.98@15.5 V 1 1 405 1 1 43 1 1 PW2 1 1 PEDOT∶PSS+WCl 6 =1∶1 1 1 100 1 1 2.46%@3.46 mA/cm 2 1 1 7.80@14.5 V 1 1 404 1 1 45 1 1 PW3 1 1 PEDOT∶PSS+WCl 6 =3∶1 1 1 100 1 1 2.60%@5.81 mA/cm 2 1 1 8.05@14.5 V 1 1 405 1 1 45 1 1 PW4 1 1 PEDOT∶PSS+WCl 6 =5∶1 1 1 100 1 1 2.25%@ 1.87 mA/cm 2 1 1 6.40@15.5 V 1 1 405 1 1 44 为比较不同HIL的空穴注入能力，制备了一系列HOC器件(器件HW、HP和HPW)并进行伏安特性( I-V )和阻抗谱分析。 器件HW:ITO/WCl 6 (0.5 mg/mL)/CBP(120 nm)/Al(100 nm); 器件HP:ITO/PEDOT∶PSS/CBP/Al; 器件HPW:ITO/PEDOT∶PSS+WCl 6 (3∶1)/CBP/Al。 图4(a) 图4(a) 显示了器件HW、HP和HPW的 I-V 特性曲线。可以看出，相同电压条件下，器件HPW的电流最大，器件HW的电流最小，可知功能层PEDOT∶PSS+WCl 6 的空穴注入能力最强。 图4(b)~(c) 图4(b)~(c) 分别是 Z-V 和 Φ-V 曲线，当电压较小时，器件都呈现高阻状态(约10 5 Ω)和近-90°的相角，表明器件在该电压条件下为绝缘状态；随着电压升高，阻抗和相角开始转变，从高阻抗值到低阻抗值的转变特征电压按器件HPW、HP和HW的顺序逐渐增大。相应的 Φ-V 曲线中-90°~0°相角转变特征电压以及 C-V 曲线电容峰值转变特征电压(如 图4(d) 图4(d) 中箭头标识)也遵循相同的顺序。这表明各HOC器件由不导电状态过渡到半导体状态的转变电压依次上升 [ 2 2 , 4 4 , 8 8 ] 。综合 I-V 、 Z-V 、 Φ-V 和 C-V 曲线分析，PEDOT∶PSS+WCl 6 具有最强的空穴注入能力，其次依次为PEDOT∶PSS和WCl 6 。 WCl 6 、PEDOT∶PSS和PEDOT∶PSS+WCl 6 薄膜在350~700 nm波长范围的吸收光谱如 图5(a) 图5(a) 所示，表明这些薄膜在近紫外波段的光吸收很弱，有利于近紫外光从发光层逃逸发射。PEDOT∶PSS+WCl 6 和PEDOT∶PSS的吸收光谱差异极小，这也进一步说明了WCl 6 在PEDOT∶PSS中具有良好的分散性和均匀性。 在大气环境中和未封装条件下，对WCl 6 、PEDOT∶PSS和PEDOT∶PSS+WCl 6 作HIL的NUV-OLED器件进行寿命测试，结果如 图5(b) 图5(b) 所示。基于WCl 6 和PEDOT∶PSS的器件，高发光强度持续时间较短。可能原因是WCl 6 具有氧化性，PEDOT∶PSS具有酸性，在ITO电极以及相邻有机功能层缺陷态较多，容易出现漏电流导致器件寿命较短。基于PEDOT∶PSS+WCl 6 掺杂层的器件老化速度显著降低，寿命有一定的改善。这可能是掺杂后溶液的稀释作用以及PEDOT∶PSS长链与W 6+ 的结合 [ 20 20 ] 改善了与相邻功能层的界面特性，使器件稳定性得以提高。 结论 1 本文通过溶液法制备了WCl 6 、PEDOT∶PSS和PEDOT∶PSS+WCl 6 ，并在NUV-OLED器件中充当HIL调控器件的光电性能。器件光电性能和发光寿命测试表明，以PEDOT∶PSS+WCl 6 作HIL、PBD为近紫外发光层，获得了EQE为2.6%、辐照度为8.05 mW/cm 2 、FWHM为45 nm、EL峰为405 nm的NUV-OLED器件。同时，器件的寿命和稳定性也得到了一定的改善。紫外-可见光吸收光谱表明HIL薄膜具有良好的近紫外光透过性。HOC器件的 I-V 、 Z-V 、 Φ-V 和 C-V 测试结果显示，各HIL的空穴注入能力按WCl 6 、PEDOT∶PSS和PEDOT∶PSS+WCl 6 的顺序逐渐增强，PEDOT∶PSS+WCl 6 优异的空穴注入调控实现了高效率NUV-OLED器件。 本文专家审稿意见及作者回复内容的下载地址:http://cjl.lightpublishing.cn/thesisDetails#10.37188/CJL.20210274. 参考文献: 苏仕健 . 新一代有机电致发光材料与器件 [J]. 科学通报 , 2016 , 61 ( 32 ): 3448 - 3452 . 新一代有机电致发光材料与器件 SU S J . A new generation of organic light-emitting materials and devices [J]. Chin. Sci. Bull. , 2016 , 61 ( 32 ): 3448 - 3452 . (in Chinese) A new generation of organic light-emitting materials and devices CHEN M Y , LIAO Y J , LIN Y , et al . Progress on ultraviolet organic electroluminescence and lasing [J]. J. Mater. Chem. C , 2020 , 8 ( 42 ): 14665 - 14694 . Progress on ultraviolet organic electroluminescence and lasing 连加荣 , 曾鹏举 . 紫外有机电致发光材料的研究进展 [J]. 现代显示 , 2010 ( 11 ): 35 - 39 . 紫外有机电致发光材料的研究进展 LIAN J R , ZENG P J . Research progress in ultraviolet organic light-emitting materials [J]. Adv. Disp. , 2010 ( 11 ): 35 - 39 . (in Chinese) Research progress in ultraviolet organic light-emitting materials ZHANG X W , YOU F J , LIU S Q , et al . Exceeding 4% external quantum efficiency in ultraviolet organic light-emitting diode using PEDOT∶PSS/MoOx double-stacked hole injection layer [J]. Appl. Phys. Lett. , 2017 , 110 ( 4 ): 043301-1-4 . Exceeding 4% external quantum efficiency in ultraviolet organic light-emitting diode using PEDOT∶PSS/MoOx double-stacked hole injection layer LI D L , YUAN Y F , XU J W , et al . Giant enhancement of external quantum efficiency in near-UV organic light-emitting diodes via device aging and impedance spectroscopy analysis [J]. Phys. Status Solidi RRL , 2021 , 15 ( 6 ): 2100041 . Giant enhancement of external quantum efficiency in near-UV organic light-emitting diodes via device aging and impedance spectroscopy analysis LUO Y J , LI S B , ZHAO Y H , et al . An ultraviolet thermally activated delayed fluorescence OLED with total external quantum efficiency over 9% [J]. Adv. Mater. , 2020 , 32 ( 32 ): 2001248-1-5 . An ultraviolet thermally activated delayed fluorescence OLED with total external quantum efficiency over 9% LI W S , ZHANG Y , ZHENG Q H , et al . Solution-processed WOx hole injection layer for efficient fluorescent blue organic light-emitting diode [J]. Curr. Appl. Phys. , 2018 , 18 ( 5 ): 583 - 589 . Solution-processed WOx hole injection layer for efficient fluorescent blue organic light-emitting diode ZHANG X W , YOU F J , ZHENG Q H , et al . Solution-processed MoOx hole injection layer towards efficient organic light-emitting diode [J]. Org. Electron. , 2016 , 39 : 43 - 49 . Solution-processed MoOx hole injection layer towards efficient organic light-emitting diode MEYER J , HAMWI S , KRÖEGER M , et al . Transition metal oxides for organic electronics:energetics,device physics and applications [J]. Adv. Mater. , 2012 , 24 ( 40 ): 5408 - 5427 . Transition metal oxides for organic electronics:energetics,device physics and applications ZHANG X W , LI W S , LING Z T , et al . Facile synthesis of solution-processed MoS2 nanosheets and their application in high-performance ultraviolet organic light-emitting diodes [J]. J. Mater. Chem. C , 2019 , 7 ( 4 ): 926 - 936 . Facile synthesis of solution-processed MoS2 nanosheets and their application in high-performance ultraviolet organic light-emitting diodes KIM C , NGUYEN T P , VAN LE Q , et al . Performances of liquid-exfoliated transition metal dichalcogenides as hole injection layers in organic light-emitting diodes [J]. Adv. Funct. Mater. , 2015 , 25 ( 28 ): 4512 - 4519 . Performances of liquid-exfoliated transition metal dichalcogenides as hole injection layers in organic light-emitting diodes WANG H H , LI D L , YUAN Y F , et al . Solution-processed WS2 and its doping in PEDOT∶PSS for tailoring hole injection in near ultraviolet organic light-emitting diodes [J]. Appl. Opt. , 2021 , 60 ( 9 ): 2610 - 2615 . Solution-processed WS2 and its doping in PEDOT∶PSS for tailoring hole injection in near ultraviolet organic light-emitting diodes SHI S W , SADHU V , MOUBAH R , et al . Solution-processable graphene oxide as an efficient hole injection layer for high luminance organic light-emitting diodes [J]. J. Mater. Chem. C , 2013 , 1 ( 9 ): 1708 - 1712 . Solution-processable graphene oxide as an efficient hole injection layer for high luminance organic light-emitting diodes ZHANG X W , ZHENG Q H , TANG Z Y , et al . Tunable hole injection of solution-processed polymeric carbon nitride towards efficient organic light-emitting diode [J]. Appl. Phys. Lett. , 2018 , 112 ( 8 ): 083302-1-4 . Tunable hole injection of solution-processed polymeric carbon nitride towards efficient organic light-emitting diode ZHENG Q H , YOU F J , XU J W , et al . Solution-processed aqueous composite hole injection layer of PEDOT∶PSS+MoOx for efficient ultraviolet organic light-emitting diode [J]. Org. Electron. , 2017 , 46 : 7 - 13 . Solution-processed aqueous composite hole injection layer of PEDOT∶PSS+MoOx for efficient ultraviolet organic light-emitting diode DOLCI S , MARCHETTI F , PAMPALONI G , et al . A systematic study on the activation of simple polyethers by MoCl5 and WCl6 [J]. Dalton Trans. , 2010 , 39 ( 22 ): 5367 - 5376 . A systematic study on the activation of simple polyethers by MoCl5 and WCl6 WU H S , ZHAO X W , WU Y Z , et al . Improving CNT-Si solar cells by metal chloride-to-oxide transformation [J]. Nano Res. , 2020 , 13 ( 2 ): 543 - 550 . Improving CNT-Si solar cells by metal chloride-to-oxide transformation ZHAN T , REN P , HUANG X F , et al . A solution-processed,ultraviolet-irradiation-derived WO3 film as anode interface layer for high-performance non-fullerene organic solar cells [J]. Solar Energy , 2021 , 216 : 211 - 216 . A solution-processed,ultraviolet-irradiation-derived WO3 film as anode interface layer for high-performance non-fullerene organic solar cells SCHAARSCHMIDT A , FARAH A A , ABY A , et al . Influence of nonadiabatic annealing on the morphology and molecular structure of PEDOT-PSS films [J]. J. Phys. Chem. B , 2009 , 113 ( 28 ): 9352 - 9355 . Influence of nonadiabatic annealing on the morphology and molecular structure of PEDOT-PSS films YUAN Y F , ZHANG X W , LI D L , et al . Tailoring hole injection of sol-gel processed WOx and its doping in PEDOT∶PSS for efficient ultraviolet organic light-emitting diodes [J]. Phys. Chem. Chem. Phys. , 2020 , 22 ( 23 ): 13214 - 13222 . Tailoring hole injection of sol-gel processed WOx and its doping in PEDOT∶PSS for efficient ultraviolet organic light-emitting diodes YAO D L , WANG J X , LI D L , et al . Facilely solution-processed lithium carbonate for tailoring electron injection in high-performance inverted near-UV organic light-emitting diodes [J]. Phys. Status Solidi A , 2021 , 218 ( 17 ): 2100222 . Facilely solution-processed lithium carbonate for tailoring electron injection in high-performance inverted near-UV organic light-emitting diodes 10.37188/CJL.20210274 TN383 + .1 A 1000-7032(2021)12-1906-08 国家自然科学基金（62065004,52063010,51762011）；广西自然科学基金（2018GXNSFDA294002）；中山市科技项目（2019B2018）；广西重点研发计划（桂科AB19110032）；广西研究生教育创新计划（YCSW2020162）资助项目 Supported by National Natural Science Foundation of China (62065004,52063010,51762011); Guangxi Natural Science Foundation (2018GXNSFDA294002); Science and Technology Project of Zhongshan (2019B2018); Key Research and Development Program of Guangxi (GuiKeAB19110032); Innovation Project of Guangxi Graduate Education (YCSW2020162) 2021-08-30 2021-09-16 2021-12-16 2021 发光学报 12 42