阴极修饰层CuPc、ZnPc、C_(60)对OLED光电性能的影响
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摘要
采用真空蒸镀法分别制备了以CuPc、ZnPc、C_(60)为阴极修饰层的OLED,对比研究了它们对OLED光电性能的影响。从能级结构、表面形貌、折射率及纳米界面等方面对载流子注入和输运进行了探讨。结果表明:修饰层使器件性能显著提高,它不仅降低OLED开启电压(最低至4.2V)、提高OLED电流密度及发光效率(最高至13.49lm/W),同时增强了器件的发光稳定性(180s后光强保持在90%以上),其中以CuPc为阴极修饰层的器件表现的性能最好。发光光谱方面,以CuPc和ZnPc作为修饰层的器件对550～650nm的红光部分略有吸收,而C_(60)作为修饰层的器件光谱则无太大变化,这是由修饰层材料的吸收系数随不同波长而变化所致。实验结果说明,若想较大程度地提高器件电性能,酞菁材料是不错的选择;若对光谱有要求,可用C_(60)做阴极修饰层。
Different materials( CuPc,ZnPc,C60) were used as the cathode buffer layers in typical OLED( ITO/TPD/Alq3/Al) prepared by evaporation,respectively. The influences of those materials on electroluminescence characteristics were investigated and relative mechanisms were discussed.Energy level structure,surface morphology,refractive index,nano-interface and some other mechanisms were used to discuss the injection and transportation of carriers. It is found that the buffer layers can evidently improve the device's performances: not only decrease the drive voltage( to 4. 2 V),but also increase the current density and efficiency( to 13. 49 lm/W),as well as enhance the stability( the intensity remained above 90% after 180 s). Device with CuPc layer achieves the best performance. Besides,CuPc and ZnPc cathode buffer layers show strong absorbing properties on OLED's spectrum between 550 nm and 650 nm,while C60 layer did not exhibit this effect. This is because the absorption coefficient of each material corresponds to different wavelengths. The results explain that CuPc and ZnPc cathode buffer layers could commendably improve OLED's characteristics,while fullerene( C60) is a good choice if there is a strict request on spectrum.
Different materials( CuPc,ZnPc,C60) were used as the cathode buffer layers in typical OLED( ITO/TPD/Alq3/Al) prepared by evaporation,respectively. The influences of those materials on electroluminescence characteristics were investigated and relative mechanisms were discussed.Energy level structure,surface morphology,refractive index,nano-interface and some other mechanisms were used to discuss the injection and transportation of carriers. It is found that the buffer layers can evidently improve the device's performances: not only decrease the drive voltage( to 4. 2 V),but also increase the current density and efficiency( to 13. 49 lm/W),as well as enhance the stability( the intensity remained above 90% after 180 s). Device with CuPc layer achieves the best performance. Besides,CuPc and ZnPc cathode buffer layers show strong absorbing properties on OLED's spectrum between 550 nm and 650 nm,while C60 layer did not exhibit this effect. This is because the absorption coefficient of each material corresponds to different wavelengths. The results explain that CuPc and ZnPc cathode buffer layers could commendably improve OLED's characteristics,while fullerene( C60) is a good choice if there is a strict request on spectrum.
引文
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[4]PENG J H,XU X J,FENG X J,et al..Fabrication of solution-processed pure blue fluorescent OLED using exciplex host[J].J.Lumin.,2018,198:19-23.
[5]LIU C K,CHEN Y H,LONG Y J,et al..Bipolar 9-linked carbazole-π-dimesitylborane fluorophores for nondoped blue OLEDs and red phosphorescent OLEDs[J].Dyes Pigm.,2018,157:101-108.
[6]LI W,ZHAO J W,LI L J,et al..Efficient solution-processed blue and white OLEDs based on a high-triplet bipolar host and a blue TADF emitter[J].Org.Electron.,2018,58:276-282.
[7]李怀坤,张方辉,程君,等.BPhen作为发光层间隔层对黄光OLED的影响[J].发光学报,2016,37(1):38-43.LI H K,ZHANG F H,CHENG J,et al..Effects of BPhen as spacer layer in light emitting layer on yellow OLED[J].Chin.J.Lumin.,2016,37(1):38-43.(in Chinese)
[8]MIAO Y,WANG K,ZHAO B,et al..High-efficiency/CRI/color stability warm white organic light-emitting diodes by incorporating ultrathin phosphorescence layers in a blue fluorescence layer[J].Nanophotonics,2018,7:295-304.
[9]张浩,王立,容佳玲,等.碳酸铯修饰Al作为反射阴极的倒置顶发射OLED器件[J].发光学报,2012,33(6):611-615.ZHANG H,WANG L,RONG J L,et al..Efficient inverted top-emitting organic light-emitting devices with cesium carbonate modified Al cathode[J].Chin.J.Lumin.,2012,33(6):611-615.(in Chinese)
[10]ANGEL F A,GAO R,WALLACE J U,et al..Silver-induced activation of 8-hydroxyquinolinato lithium as electron injection material in single-stack and tandem OLED devices[J].Org.Electron.,2018,59:220-223.
[11]WEIJER P V,LU K,JANSSEN R R,et al..Mechanism of the operational effect of black spot growth in OLEDs[J].Org.Electron.,2016,37:155-162.
[12]刘晋红,张方辉.OLED薄膜干燥剂的制备及其对OLED的影响[J].发光学报,2017,38(1):76-84.LIU J H,ZHANG F H.Preparation of OLED desiccant film and the impact for OLED[J].Chin.J.Lumin.,2017,38(1):76-84.(in Chinese)
[13]段玮,李晟,张浩,等.基于Al2O3封装薄膜的OLED水汽透过率测试方法及系统研究[J].发光学报,2016,37(1):88-93.DUAN W,LI S,ZHANG H,et al..Test method and system of water vapor transmission rate based on Al2O3encapsulated thin-film for OLEDs[J].Chin.J.Lumin.,2016,37(1):88-93.(in Chinese)
[14]KANG D J,PARK G U,PARK H Y,et al..A high-performance transparent moisture barrier using surface-modified nanoclay composite for OLED encapsulation[J].Prog.Org.Coatings,2018,118:66-71.
[15]郭颂,杜晓刚,刘晓云,等.氧化石墨烯作为共蒸镀掺杂材料在OLED中的应用[J].发光学报,2013,34(5):595-599.GUO S,DU X G,LIU X Y,et al..Graphene oxide as doping material for assembling OLEDs via thermal co-evaporation with NPB and Alq3[J].Chin.J.Lumin.,2013,34(5):595-599.(in Chinese)
[16]李菀丽,武聪伶,苗艳勤,等.二氧化钛改性8-羟基喹啉铝对有机电致发光器件抗老化性能的提高[J].发光学报,2015,36(2):219-224.LI W L,WU C L,MIAO Y Q,et al..Ti O2doped Alq3as emitting layer to improve the anti-aging performance of OLED[J].Chin.J.Lumin.,2015,36(2):219-224.(in Chinese)
[17]LIU Y F,AN M Y,ZHANG X L,et al..Enhanced efficiency of organic light-emitting devices with corrugated nanostructures based on soft nano-printing lithography[J].Appl.Phys.Lett.,2016,109(19):193301.
[18]MANN V,RASTOGI V.Dielectric nanoparticles for the enhancement of OLED light extraction efficiency[J].Opt.Commun.,2017,387:202-207.
[19]WEI B W,WU X K,LIAN L,et al..A highly conductive and smooth Ag NW/PEDOT∶PSS film treated by hot-pressing as electrode for organic light emitting diode[J].Org.Electron.,2017,43:182-188.
[20]KUMAR G,LI Y D,BIRING S,et al..Highly efficient ITO-free organic light-emitting diodes employing a roughened ultra-thin silver electrode[J].Org.Electron.,2017,42:52-58.
[21]JANG S,HAN S H,LEE J Y,et al..Pyrimidine based hole-blocking materials with high triplet energy and glass transition temperature for blue phosphorescent OLEDs[J].Synth.Met.,2018,239:43-50.
[22]XIANG N,GAO Z X,TIAN G J,et al..Novel fluorene/indole-based hole transport materials with high thermal stability for efficient OLEDs[J].Dyes Pigm.,2017,137:36-42.
[23]DONG F X,DING R,HOTTA S,et al..Improved performance of organic light-emitting devices based on 1,4-bis(5-phenyl-thiophen-2-yl)benzene single crystal by using an anodic buffer layer[J].Opt.Commun.,2017,392:247-251.
[24]赵丹,徐登辉,杨在发,等.旋涂法酸处理PEDOT∶PSS薄膜对OLED性能的影响[J].发光学报,2016,37(2):174-180.ZHAO D,XU D H,YANG Z F,et al..Optical and electrical properties of PEDOT∶PSS films treated by spin coating with acid for organic light-emitting diodes[J].Chin.J.Lumin.,2016,37(2):174-180.(in Chinese)
[25]LV Z Y,DENG Z B,ZHENG C,et al..The effect of various electrodes on the properties of electroluminescent devices with potassium chloride inside tris(8-hydroxyquinoline)aluminum[J].Displays,2011,32(3):113-117.
[26]黄春辉,李富友,黄维.有机电致发光材料与器件导论[M].上海:复旦大学出版社,2005.HUANG C H,LI F Y,HUANG W.Introduction to Organic Light-emitting Materials and Devices[M].Shanghai:Fudan University Press,2005.(in Chinese)
[27]HUNG L S,TANG C W,MASON M G.Enhanced electron injection in organic electroluminescence devices using an Al/Li F electrode[J].Appl.Phys.Lett.,1997,70:152-154.
[28]HAN K,YI Y,SONG W J,et al..Dual enhancing properties of Li F with varying positions inside organic light-emitting devices[J].Org.Electron.,2008,9:30-38.
[29]TADAYYON S M,GRANDIN H M,GRIFFITHS K,et al..Cu Pc buffer layer role in OLED performance:a study of the interfacial band energies[J].Org.Electron.,2004,5(4):157-166.
[30]LV Z Y,DENG Z B,XU D H,et al..Efficient organic light-emitting diodes with C60buffer layer[J].Displays,2009,30(1):23-26.
[31]KANG H S,PARK K N,CHO Y R,et al..Enhanced performance of organic electroluminescence diodes with a 2-TNATA∶C60hole injection layer[J].J.Ind.Eng.Chem.,2009,15(5):752-757.
[32]LIN W C,LIN Y C,WANG W B,et al..Effect of fabrication process on the microstructure and the efficiency of organic light-emitting diode[J].Org.Electron.,2009,10(3):459-464.
[33]LEE J H,LIAO C C,HU P J,et al..High contrast ratio organic light-emitting devices based on Cu PC as electron transport material[J].Synth.Met.,2004,144(3):279-283.
[34]KIM I,HAVERINEN H M,LI J,et al..Enhanced power conversion efficiency of p-i-n type organic solar cells by employing a p-layer of palladium phthalocyanine[J].Appl.Phys.Lett.,2010,97(20):203301.
[35]FENG X D,HUANG C J,LUI V,et al..Ohmic cathode for low-voltage organic light-emitting diodes[J].Appl.Phys.Lett.,2005,86(14):143511.
[36]FENTER P,SCHREIBER F,BULOVIC V.Applied surface science thermally induced failure mechanisms of organic light emitting device structures probed by X-ray specular reflectivity[J].Chem.Phys.Lett.,1997,277(5-6):521-526.
[37]LEE T W,PARK O O.The effect of different heat treatments on the luminescence efficiency of polymer light-emitting diodes[J].Adv.Mater.,2000,12(11):801-804.
[38]LIU Z T,KWOK H S,DJURISIC A B.The optical functions of metal phthalocyanines[J].J.Phys.D:Appl.Phys.,2004,37(5):678-688.
[39]GUO J X,SUN Z,TAY B K,et al..Field emission from modified nanocomposite carbon films prepared by filtered cathodic vacuum arc at high negative pulsed bias[J].Appl.Surf.Sci.,2003,214(1-4):351-358.
[40]LEE Y J,LEE H,BYUN Y,et al..Study of thermal degradation of organic light emitting device structures by X-ray scattering[J].Thin Solid Films,2007,515(14):5674-5677.
[41]胡远川,王立铎,董桂芳,等.铜酞菁缓冲层改善有机电致发光器件性能的机理研究[J].功能材料,2002,33(3):321-323.HU Y C,WANG L D,DONG G F,et al..Mechanism of improving the performance of organic electroluminescent devices by using Cu Pc as buffer layer[J].J.Funct.Mater.,2002,33(3):321-323.(in Chinese)
[2]RAUPP S M,MERKLEIN L,PATHAK M,et al..An experimental study on the reproducibility of different multilayer OLED materials processed by slot die coating[J].Chem.Eng.Sci.,2017,160:113-120.
[3]WEI A C,SZE J R.Modeling OLED lighting using Monte Carlo ray tracing and rigorous coupling wave analyses[J].Opt.Commun.,2016,380:394-400.
[4]PENG J H,XU X J,FENG X J,et al..Fabrication of solution-processed pure blue fluorescent OLED using exciplex host[J].J.Lumin.,2018,198:19-23.
[5]LIU C K,CHEN Y H,LONG Y J,et al..Bipolar 9-linked carbazole-π-dimesitylborane fluorophores for nondoped blue OLEDs and red phosphorescent OLEDs[J].Dyes Pigm.,2018,157:101-108.
[6]LI W,ZHAO J W,LI L J,et al..Efficient solution-processed blue and white OLEDs based on a high-triplet bipolar host and a blue TADF emitter[J].Org.Electron.,2018,58:276-282.
[7]李怀坤,张方辉,程君,等.BPhen作为发光层间隔层对黄光OLED的影响[J].发光学报,2016,37(1):38-43.LI H K,ZHANG F H,CHENG J,et al..Effects of BPhen as spacer layer in light emitting layer on yellow OLED[J].Chin.J.Lumin.,2016,37(1):38-43.(in Chinese)
[8]MIAO Y,WANG K,ZHAO B,et al..High-efficiency/CRI/color stability warm white organic light-emitting diodes by incorporating ultrathin phosphorescence layers in a blue fluorescence layer[J].Nanophotonics,2018,7:295-304.
[9]张浩,王立,容佳玲,等.碳酸铯修饰Al作为反射阴极的倒置顶发射OLED器件[J].发光学报,2012,33(6):611-615.ZHANG H,WANG L,RONG J L,et al..Efficient inverted top-emitting organic light-emitting devices with cesium carbonate modified Al cathode[J].Chin.J.Lumin.,2012,33(6):611-615.(in Chinese)
[10]ANGEL F A,GAO R,WALLACE J U,et al..Silver-induced activation of 8-hydroxyquinolinato lithium as electron injection material in single-stack and tandem OLED devices[J].Org.Electron.,2018,59:220-223.
[11]WEIJER P V,LU K,JANSSEN R R,et al..Mechanism of the operational effect of black spot growth in OLEDs[J].Org.Electron.,2016,37:155-162.
[12]刘晋红,张方辉.OLED薄膜干燥剂的制备及其对OLED的影响[J].发光学报,2017,38(1):76-84.LIU J H,ZHANG F H.Preparation of OLED desiccant film and the impact for OLED[J].Chin.J.Lumin.,2017,38(1):76-84.(in Chinese)
[13]段玮,李晟,张浩,等.基于Al2O3封装薄膜的OLED水汽透过率测试方法及系统研究[J].发光学报,2016,37(1):88-93.DUAN W,LI S,ZHANG H,et al..Test method and system of water vapor transmission rate based on Al2O3encapsulated thin-film for OLEDs[J].Chin.J.Lumin.,2016,37(1):88-93.(in Chinese)
[14]KANG D J,PARK G U,PARK H Y,et al..A high-performance transparent moisture barrier using surface-modified nanoclay composite for OLED encapsulation[J].Prog.Org.Coatings,2018,118:66-71.
[15]郭颂,杜晓刚,刘晓云,等.氧化石墨烯作为共蒸镀掺杂材料在OLED中的应用[J].发光学报,2013,34(5):595-599.GUO S,DU X G,LIU X Y,et al..Graphene oxide as doping material for assembling OLEDs via thermal co-evaporation with NPB and Alq3[J].Chin.J.Lumin.,2013,34(5):595-599.(in Chinese)
[16]李菀丽,武聪伶,苗艳勤,等.二氧化钛改性8-羟基喹啉铝对有机电致发光器件抗老化性能的提高[J].发光学报,2015,36(2):219-224.LI W L,WU C L,MIAO Y Q,et al..Ti O2doped Alq3as emitting layer to improve the anti-aging performance of OLED[J].Chin.J.Lumin.,2015,36(2):219-224.(in Chinese)
[17]LIU Y F,AN M Y,ZHANG X L,et al..Enhanced efficiency of organic light-emitting devices with corrugated nanostructures based on soft nano-printing lithography[J].Appl.Phys.Lett.,2016,109(19):193301.
[18]MANN V,RASTOGI V.Dielectric nanoparticles for the enhancement of OLED light extraction efficiency[J].Opt.Commun.,2017,387:202-207.
[19]WEI B W,WU X K,LIAN L,et al..A highly conductive and smooth Ag NW/PEDOT∶PSS film treated by hot-pressing as electrode for organic light emitting diode[J].Org.Electron.,2017,43:182-188.
[20]KUMAR G,LI Y D,BIRING S,et al..Highly efficient ITO-free organic light-emitting diodes employing a roughened ultra-thin silver electrode[J].Org.Electron.,2017,42:52-58.
[21]JANG S,HAN S H,LEE J Y,et al..Pyrimidine based hole-blocking materials with high triplet energy and glass transition temperature for blue phosphorescent OLEDs[J].Synth.Met.,2018,239:43-50.
[22]XIANG N,GAO Z X,TIAN G J,et al..Novel fluorene/indole-based hole transport materials with high thermal stability for efficient OLEDs[J].Dyes Pigm.,2017,137:36-42.
[23]DONG F X,DING R,HOTTA S,et al..Improved performance of organic light-emitting devices based on 1,4-bis(5-phenyl-thiophen-2-yl)benzene single crystal by using an anodic buffer layer[J].Opt.Commun.,2017,392:247-251.
[24]赵丹,徐登辉,杨在发,等.旋涂法酸处理PEDOT∶PSS薄膜对OLED性能的影响[J].发光学报,2016,37(2):174-180.ZHAO D,XU D H,YANG Z F,et al..Optical and electrical properties of PEDOT∶PSS films treated by spin coating with acid for organic light-emitting diodes[J].Chin.J.Lumin.,2016,37(2):174-180.(in Chinese)
[25]LV Z Y,DENG Z B,ZHENG C,et al..The effect of various electrodes on the properties of electroluminescent devices with potassium chloride inside tris(8-hydroxyquinoline)aluminum[J].Displays,2011,32(3):113-117.
[26]黄春辉,李富友,黄维.有机电致发光材料与器件导论[M].上海:复旦大学出版社,2005.HUANG C H,LI F Y,HUANG W.Introduction to Organic Light-emitting Materials and Devices[M].Shanghai:Fudan University Press,2005.(in Chinese)
[27]HUNG L S,TANG C W,MASON M G.Enhanced electron injection in organic electroluminescence devices using an Al/Li F electrode[J].Appl.Phys.Lett.,1997,70:152-154.
[28]HAN K,YI Y,SONG W J,et al..Dual enhancing properties of Li F with varying positions inside organic light-emitting devices[J].Org.Electron.,2008,9:30-38.
[29]TADAYYON S M,GRANDIN H M,GRIFFITHS K,et al..Cu Pc buffer layer role in OLED performance:a study of the interfacial band energies[J].Org.Electron.,2004,5(4):157-166.
[30]LV Z Y,DENG Z B,XU D H,et al..Efficient organic light-emitting diodes with C60buffer layer[J].Displays,2009,30(1):23-26.
[31]KANG H S,PARK K N,CHO Y R,et al..Enhanced performance of organic electroluminescence diodes with a 2-TNATA∶C60hole injection layer[J].J.Ind.Eng.Chem.,2009,15(5):752-757.
[32]LIN W C,LIN Y C,WANG W B,et al..Effect of fabrication process on the microstructure and the efficiency of organic light-emitting diode[J].Org.Electron.,2009,10(3):459-464.
[33]LEE J H,LIAO C C,HU P J,et al..High contrast ratio organic light-emitting devices based on Cu PC as electron transport material[J].Synth.Met.,2004,144(3):279-283.
[34]KIM I,HAVERINEN H M,LI J,et al..Enhanced power conversion efficiency of p-i-n type organic solar cells by employing a p-layer of palladium phthalocyanine[J].Appl.Phys.Lett.,2010,97(20):203301.
[35]FENG X D,HUANG C J,LUI V,et al..Ohmic cathode for low-voltage organic light-emitting diodes[J].Appl.Phys.Lett.,2005,86(14):143511.
[36]FENTER P,SCHREIBER F,BULOVIC V.Applied surface science thermally induced failure mechanisms of organic light emitting device structures probed by X-ray specular reflectivity[J].Chem.Phys.Lett.,1997,277(5-6):521-526.
[37]LEE T W,PARK O O.The effect of different heat treatments on the luminescence efficiency of polymer light-emitting diodes[J].Adv.Mater.,2000,12(11):801-804.
[38]LIU Z T,KWOK H S,DJURISIC A B.The optical functions of metal phthalocyanines[J].J.Phys.D:Appl.Phys.,2004,37(5):678-688.
[39]GUO J X,SUN Z,TAY B K,et al..Field emission from modified nanocomposite carbon films prepared by filtered cathodic vacuum arc at high negative pulsed bias[J].Appl.Surf.Sci.,2003,214(1-4):351-358.
[40]LEE Y J,LEE H,BYUN Y,et al..Study of thermal degradation of organic light emitting device structures by X-ray scattering[J].Thin Solid Films,2007,515(14):5674-5677.
[41]胡远川,王立铎,董桂芳,等.铜酞菁缓冲层改善有机电致发光器件性能的机理研究[J].功能材料,2002,33(3):321-323.HU Y C,WANG L D,DONG G F,et al..Mechanism of improving the performance of organic electroluminescent devices by using Cu Pc as buffer layer[J].J.Funct.Mater.,2002,33(3):321-323.(in Chinese)