The performance of polymer light emitting devices(PLEDs)based on polyvinyl carbazole(PVK)is improved by introducing a nanoscale interfacial thin layer,made of poly(ethylene oxide)(PEO),between the calcium cathode and ...The performance of polymer light emitting devices(PLEDs)based on polyvinyl carbazole(PVK)is improved by introducing a nanoscale interfacial thin layer,made of poly(ethylene oxide)(PEO),between the calcium cathode and the PVK emissive layer.It is believed that the PEO layer plays a key role in enhancing the device performance.In comparison to the device with Ca/Al as the cathode,the performance of the PLED with PEO/Ca/Al cathode,including the driving voltage,luminance efficiency is significantly improved.These improvements are attributed to the introduction of a thin layer of PEO that can lower the interfacial barrier and facilitate electron injection.展开更多
The AlGaN-based deep ultraviolet light-emitting diodes(LED) with double electron blocking layers(d-EBLs) on both sides of the active region are investigated theoretically. They possess many excellent performances ...The AlGaN-based deep ultraviolet light-emitting diodes(LED) with double electron blocking layers(d-EBLs) on both sides of the active region are investigated theoretically. They possess many excellent performances compared with the conventional structure with only a single electron blocking layer, such as a higher recombination rate, improved light output power and internal quantum efficiency(IQE). The reasons can be concluded as follows. On the one hand, the weakened electrostatic field within the quantum wells(QWs) enhances the electron–hole spatial overlap in QWs, and therefore increases the probability of radioactive recombination. On the other hand, the added n-AlGaN layer can not only prevent holes from overflowing into the n-side region but also act as another electron source, providing more electrons.展开更多
Several highly efficient iridium-complex polymer light-emitting devices (PLEDs) are fabricated, with a newly synthesized blue conjugated polymer, poly[(9,9-bis(4-(2-ethylhexyloxy)phenyl)-fluorene)-co-(3,7-dib...Several highly efficient iridium-complex polymer light-emitting devices (PLEDs) are fabricated, with a newly synthesized blue conjugated polymer, poly[(9,9-bis(4-(2-ethylhexyloxy)phenyl)-fluorene)-co-(3,7-dibenziothiene-S,S- dioxide15)] (PPF-3,TSO15), chosen as host. High luminous efficiencies of 7.4 cd.A-1 and 27.4 cd.A-1 are achieved in red and green PLEDs, respectively, by optimizing the doping concentrations of red phosphorescent dye iridium bis(1- phenylisoquinoline) (acetylacetonate) (Ir(piq)) and green phosphorescent dye iridium tris(2-(4-tolyl)pyridinato-N, C2') (Ir(mppy)3).Furthermore, highly efficient white PLEDs (WPLEDs) with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.35, 0.38) are successfully produced by carefully controlling the doping concentration of the irid- ium complex. The obtained WPLEDs show maximal efficiencies of 14.4 cd.A-1 and 10.1 lm.W-1, which are comparable to those of incandescent bulbs. Moreover, the electroluminescent spectrum of the white device with an initial luminance of about 1000 cd.m-2 is stable, subject to constant applied current stress, indicating that good device stability can be obtained in this system.展开更多
Fluorescence/phosphorescence hybrid white organic light-emitting devices(WOLEDs) based on double emitting layers(EMLs) with high color stability are fabricated.The simplified EMLs consist of a non-doped blue therm...Fluorescence/phosphorescence hybrid white organic light-emitting devices(WOLEDs) based on double emitting layers(EMLs) with high color stability are fabricated.The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence(TADF) layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone(DMAC-DPS) and an ultrathin non-doped yellow phosphorescence layer employing bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2']iridium(acetylacetonate)((tbt)_2Ir(acac)).Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline(Bphen) and 1,3,5-tris(2-Nphenylbenzimidazolyl) benzene(TPBi) are selected as the electron transporting layer(ETL),and the thickness of yellow EML is adjusted to optimize device performance.The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l'Eclairage(CIE) coordinates variation of(0.017,0.009) at a luminance ranging from 52 cd/m^2 to 6998 cd/m^2.The TPBi-based device yields a high efficiency with a maximum external quantum efficiency(EQE),current efficiency,and power efficiency of 10%,21.1 cd/A,and 21.3 lm/W,respectively.The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer,so that Forster energy transfer(FRET)from DMAC-DPS to(tbt)_2Ir(acac) is dominant,which is beneficial to keep the color stable.The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.展开更多
Polarized red, green, and blue light emitting diodes(LEDs) are successfully fabricated using polyfluorene and its derivatives, namely, poly(9,9-dioctylfluorene)(PFO), poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8BT...Polarized red, green, and blue light emitting diodes(LEDs) are successfully fabricated using polyfluorene and its derivatives, namely, poly(9,9-dioctylfluorene)(PFO), poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8BT),and poly(triphenylamine-co-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole-co-benzo[c]thiadiazole-co-9,9-dioctyl-9 Hfluorene)(Red F).Rubbed hole transport layer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate)(PEDOT:PSS)is employed in the devices as the alignment layer to achieve fully monodomain alignment in all polymer layers.Red F is blended with F8BT to realize the polarized electroluminescence of red light(dichroic ratio ~3.3), despite having no liquid crystallinity itself.Comparing PFO/F8BT blend to F8BT, higher efficiency of polarized emission is found due to the energy transfer.All the polarized LEDs exhibit pronounced dichroism and efficient polarized emission compared to the non-alignment regular devices.展开更多
We investigate the electron injection effect of inserting a thin aluminum(Al) layer into cesium carbonate(Cs2CO3)injection layer. Two groups of organic light-emitting devices(OLEDs) are fabricated. For the first...We investigate the electron injection effect of inserting a thin aluminum(Al) layer into cesium carbonate(Cs2CO3)injection layer. Two groups of organic light-emitting devices(OLEDs) are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device's maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al–O–Cs complex, and the amount of the Al–O–Cs complex can be controlled by adjusting the thickness of the thin Al layer.展开更多
A new structure containing negative refractive index dielectric layer(NRIDL) is introduced into microcavity. The properties of the new microcavity organic light-emitting devices(MOLEDs) are investigated. In the experi...A new structure containing negative refractive index dielectric layer(NRIDL) is introduced into microcavity. The properties of the new microcavity organic light-emitting devices(MOLEDs) are investigated. In the experiment, the transfer matrix method is adopted. The dependence of reflectance and transmittance on the refractive index and thickness of NRIDL are analyzed in detail. Compared with the electroluminescence spectra of non-NRIDL diodes, the line widths of the spectra of the MOLEDs are narrower and all the peaks enhance. The results show that the new structure is beneficial to improve the performance and reduce the thickness of microcavity devices.展开更多
We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode (OLED) by using the charge control layers (CCLs) based on Alq3 . The CCLs that are inserted into the emitting layers (EMLs...We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode (OLED) by using the charge control layers (CCLs) based on Alq3 . The CCLs that are inserted into the emitting layers (EMLs) could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2 , which is about 2.19 times higher than that of the control device (CD) without the CCL, and the maximal luminance is 19.660 cd/m2 at 12V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.展开更多
A 10-nm-thick molybdenum tri-oxide(MoO3) thin film was used as the interconnector layer in tandem organic lightemitting devices(OLEDs).The tandem OLEDs with two identical emissive units consisting of N,N-bis(naph...A 10-nm-thick molybdenum tri-oxide(MoO3) thin film was used as the interconnector layer in tandem organic lightemitting devices(OLEDs).The tandem OLEDs with two identical emissive units consisting of N,N-bis(naphthalen-1-yl)N,N-bis(phenyl)-benzidine(NPB) /tris(8-hydroxyquinoline) aluminum(Alq3) exhibited current efficiency-current density characteristics superior to the conventional single-unit devices.At 20 mA/cm2,the current efficiency of the tandem OLEDs using the interconnector layers of MoO3 thin film was about 4.0 cd/A,which is about twice that of the corresponding conventional single-unit device(1.8cd/A).The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200cd/m2.The experimental results demonstrated that a MoO3 thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs.Such an interconnector layer can be easily fabricated by simple thermal evaporation,greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers.A possible explanation was proposed for the carrier generation of the MoO3 interconnector layer.展开更多
SiO2Al2O3 double dielectric stack layer was deposited on the surface of the GaN-based light-emitting diode (LED). The double dielectric stack layer enhances both the electrical characteristics and the optical output p...SiO2Al2O3 double dielectric stack layer was deposited on the surface of the GaN-based light-emitting diode (LED). The double dielectric stack layer enhances both the electrical characteristics and the optical output power of the LED because the first Al2O3 layer plays a role of effectively passivating the p-GaN surface and the second lower index SiO2 layer increases the critical angle of the light emitted from the LED surface. In addition, the effect of the Fresnel reflection is also responsible for the enhancement in output power of the double dielectric passivated LED. The leakage current of the LED passivated with Al2O3 layer was -3.46 × 10-11 A at -5 V, at least two and three orders lower in magnitude compared to that passivated with SiO2 layer (-7.14 × 10-9 A) and that of non-passivated LED (-1.9 × 10-8 A), respectively, which indicates that the Al2O3 layer is very effective in passivating the exposed GaN surface after dry etch and hence reduces nonradiative recombination as well as reabsorption of the emitted light near the etched surface.展开更多
Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to the...Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by 'rebuilding' cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination. In the meantime, we recapture the findings from thesearch for suitable OLED packaging materials, in particular polymer composites, which provide both heat dissipation andmoisture resistance, in addition to electrical insulation.展开更多
We fabricate a kind of novel efficient blue fluorescent organic light emitting device(OLED) based on p-n heterojunctions composed of hole transporting layer(HTL) N,N '-bis(naphthalen-1-yl)-N,N '-bis(phenyl)-...We fabricate a kind of novel efficient blue fluorescent organic light emitting device(OLED) based on p-n heterojunctions composed of hole transporting layer(HTL) N,N '-bis(naphthalen-1-yl)-N,N '-bis(phenyl)-benzidine(NPB) and electron transporting layer(ETL) 4,7-diphnenyl-1,10-phenanthroline(BPhen),into which a new blue material,DNCA(a derivation of N 6,N 6,N 12,N 12-tetrap-tolylchrysene-6,12-diamine),is partially doped simultaneously,and double emitting layers are configured.With a turn-on voltage of 2.6 V at 1 cd/m 2,this type of OLED presents a maximum luminance efficiency(η max) of 8.83 cd/A at 5.818 mA/cm 2 and a maximum luminance of over 40000 cd/m 2.Meanwhile,the Commission Internationale De L'Eclairage(CIE) coordinates of this device change slightly from(0.13,0.27) to(0.13,0.23) as the driving voltage increases from 3 V to 11 V.This improvement in the electroluminescent characteristics is attributed mainly to the ideal p-n heterojunction which can confine and distribute excitons evenly on two sides of the heterojunction interface so as to improve the carrier combination rate and expand the light-emitting region.展开更多
The influence of different modification methods on the surface properties of indium-tin-oxide (ITO) electrodes were investigated by measurements of chemical composition,surface roughness,sheet resistance,contact angle...The influence of different modification methods on the surface properties of indium-tin-oxide (ITO) electrodes were investigated by measurements of chemical composition,surface roughness,sheet resistance,contact angle and surface free energy.Experimental results demonstrate that oxygen plasma treatment more effectively optimizes the surface properties of ITO electrodes compared with the other treatments.Furthermore,the polymer light-emitting electrochemical cells (PLECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized.It is found that oxygen plasma treatment on the ITO electrode enhances injection current,luminance and efficiency,thereby improves the device characteristics of the PLECs.展开更多
Efficient white-polymer-light-emitting devices (WPLEDs) have been fabricated with a single emitting layer containing a hole-transporting host polymer,poly(N-vinylcarbzole),and an electron-transporting auxiliary,1,3-bi...Efficient white-polymer-light-emitting devices (WPLEDs) have been fabricated with a single emitting layer containing a hole-transporting host polymer,poly(N-vinylcarbzole),and an electron-transporting auxiliary,1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]-phenylene,codoped with two phosphorescent dyes:Iridium(III)bis (2-(4,6-difluorophenyl)-pyridinato-N,C2') picolinate (FIrpic) and home-made Ir-G2 for blue and red emission,respectively.With the structure of ITO/PEDOT:PSS 4083(40 nm)/emission layer(80 nm)/Ba(4 nm)/Al(120 nm),the device showed a maximal luminous efficiency (LE) of 13.5 cd A-1(corresponding to an external quantum efficiency (EQE) of 6.8%),and a peak power efficiency (PE) of 6.5 lm W-1 at 6.0 V.Meanwhile,the device exhibited pure white emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.34,0.35) at a current density of 12 mA cm-2,which is very close to the equi-energy white point with CIE coordinates of (0.33,0.33).The device performance can be further optimized when more balanced hole/electron injection is achieved by incorporating a lower conducting type anode buffer layer (PEDOT:PSS) and incorporating poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorenene)-alt-2,7-(9,9-dioctyfluorene)] (PFN) as an electron injection layer at the cathode.The optimized device showed an LE of 24.6 cd A-1 (with an EQE of 14.1%),while the peak power efficiency reached 12.66 lm W-1.Moreover,the WPLEDs showed good electroluminescence (EL) stability over a wide range of operating current density and luminance.展开更多
A series of alkali metal salts doped pluronic block copolymer F127 were used as electron injection/transport layers (ETLs) for polymer light-emitting diodes with poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylen...A series of alkali metal salts doped pluronic block copolymer F127 were used as electron injection/transport layers (ETLs) for polymer light-emitting diodes with poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene] (P-PPV) as the emission layer. It was found that the electron transport capability of F127 can be effectively enhanced by doping with alkali metal salts. By using Li2CO3 (15%) doped F127 as ETL, the resulting device exhibited improved performance with a maximum luminous efficiency (LE) of 13.59 cd/A and a maximum brightness of 5529 cd/m2, while the device with undoped F127 as ETL only showed a maximum LE of 8.78 cd/A and a maximum brightness of 2952 cd/m2. The effects of the doping concentration, cations and anions of the alkali metal salts on the performance of the resulting devices were investigated. It was found that most of the alkali metal salt dopants can dramatically enhance the electron transport capability of F127 ETL and the performance of the resulting devices was greatly improved.展开更多
基金the Office of R&D,National Cheng Kung University,Taiwan
文摘The performance of polymer light emitting devices(PLEDs)based on polyvinyl carbazole(PVK)is improved by introducing a nanoscale interfacial thin layer,made of poly(ethylene oxide)(PEO),between the calcium cathode and the PVK emissive layer.It is believed that the PEO layer plays a key role in enhancing the device performance.In comparison to the device with Ca/Al as the cathode,the performance of the PLED with PEO/Ca/Al cathode,including the driving voltage,luminance efficiency is significantly improved.These improvements are attributed to the introduction of a thin layer of PEO that can lower the interfacial barrier and facilitate electron injection.
基金Project supported by the Special Strategic Emerging Industries of Guangdong Province,China(Grant No.2012A080304006)the Major Scientific and Technological Projects of Zhongshan City,Guangdong Province,China(Grant No.2014A2FC204)the Forefront of Technology Innovation and Key Technology Projects of Guangdong Province,China(Grant Nos.2014B010121001 and 2014B010119004)
文摘The AlGaN-based deep ultraviolet light-emitting diodes(LED) with double electron blocking layers(d-EBLs) on both sides of the active region are investigated theoretically. They possess many excellent performances compared with the conventional structure with only a single electron blocking layer, such as a higher recombination rate, improved light output power and internal quantum efficiency(IQE). The reasons can be concluded as follows. On the one hand, the weakened electrostatic field within the quantum wells(QWs) enhances the electron–hole spatial overlap in QWs, and therefore increases the probability of radioactive recombination. On the other hand, the added n-AlGaN layer can not only prevent holes from overflowing into the n-side region but also act as another electron source, providing more electrons.
基金Project supported by the National Basic Research Program of China (Grant No. 2009CB623602)the National Natural Science Foundation of China (Grant No. U0634003)
文摘Several highly efficient iridium-complex polymer light-emitting devices (PLEDs) are fabricated, with a newly synthesized blue conjugated polymer, poly[(9,9-bis(4-(2-ethylhexyloxy)phenyl)-fluorene)-co-(3,7-dibenziothiene-S,S- dioxide15)] (PPF-3,TSO15), chosen as host. High luminous efficiencies of 7.4 cd.A-1 and 27.4 cd.A-1 are achieved in red and green PLEDs, respectively, by optimizing the doping concentrations of red phosphorescent dye iridium bis(1- phenylisoquinoline) (acetylacetonate) (Ir(piq)) and green phosphorescent dye iridium tris(2-(4-tolyl)pyridinato-N, C2') (Ir(mppy)3).Furthermore, highly efficient white PLEDs (WPLEDs) with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.35, 0.38) are successfully produced by carefully controlling the doping concentration of the irid- ium complex. The obtained WPLEDs show maximal efficiencies of 14.4 cd.A-1 and 10.1 lm.W-1, which are comparable to those of incandescent bulbs. Moreover, the electroluminescent spectrum of the white device with an initial luminance of about 1000 cd.m-2 is stable, subject to constant applied current stress, indicating that good device stability can be obtained in this system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61675041 and 61605253)the Foundation for Innovation Research Groups of the National Natural Science Foundation of China(Grant No.61421002)the Science&Technology Department Program of Sichuan Province,China(Grant No.2016HH0027)
文摘Fluorescence/phosphorescence hybrid white organic light-emitting devices(WOLEDs) based on double emitting layers(EMLs) with high color stability are fabricated.The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence(TADF) layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone(DMAC-DPS) and an ultrathin non-doped yellow phosphorescence layer employing bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2']iridium(acetylacetonate)((tbt)_2Ir(acac)).Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline(Bphen) and 1,3,5-tris(2-Nphenylbenzimidazolyl) benzene(TPBi) are selected as the electron transporting layer(ETL),and the thickness of yellow EML is adjusted to optimize device performance.The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l'Eclairage(CIE) coordinates variation of(0.017,0.009) at a luminance ranging from 52 cd/m^2 to 6998 cd/m^2.The TPBi-based device yields a high efficiency with a maximum external quantum efficiency(EQE),current efficiency,and power efficiency of 10%,21.1 cd/A,and 21.3 lm/W,respectively.The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer,so that Forster energy transfer(FRET)from DMAC-DPS to(tbt)_2Ir(acac) is dominant,which is beneficial to keep the color stable.The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61874058,51861145301,and 61376023)the National Key Basic Research Program of China(Grant No.2015CB932203)+2 种基金China Postdoctoral Science Foundation(Grant No.2018M642283)the Synergetic Innovation Center for Organic Electronics and Information Displays,Chinathe Priority Academic Program Development Fund of Jiangsu Higher Education Institutions(PAPD)in China
文摘Polarized red, green, and blue light emitting diodes(LEDs) are successfully fabricated using polyfluorene and its derivatives, namely, poly(9,9-dioctylfluorene)(PFO), poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8BT),and poly(triphenylamine-co-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole-co-benzo[c]thiadiazole-co-9,9-dioctyl-9 Hfluorene)(Red F).Rubbed hole transport layer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate)(PEDOT:PSS)is employed in the devices as the alignment layer to achieve fully monodomain alignment in all polymer layers.Red F is blended with F8BT to realize the polarized electroluminescence of red light(dichroic ratio ~3.3), despite having no liquid crystallinity itself.Comparing PFO/F8BT blend to F8BT, higher efficiency of polarized emission is found due to the energy transfer.All the polarized LEDs exhibit pronounced dichroism and efficient polarized emission compared to the non-alignment regular devices.
基金supported by the National Natural Science Foundation of China(Grant No.60906022)the Natural Science Foundation of Tianjin,China(Grant No.10JCYBJC01100)+2 种基金the Scientific Developing Foundation of Tianjin Education Commission,China(Grant No.2011ZD02)the Key Science and Technology Support Program of Tianjin,China(Grant No.14ZCZDGX00006)the National High Technology Research and Development Program of China(Grant No.2013AA014201)
文摘We investigate the electron injection effect of inserting a thin aluminum(Al) layer into cesium carbonate(Cs2CO3)injection layer. Two groups of organic light-emitting devices(OLEDs) are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device's maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al–O–Cs complex, and the amount of the Al–O–Cs complex can be controlled by adjusting the thickness of the thin Al layer.
基金Natural Science Research Item of Education Department of Henan Province(2008A430009)Doctor Foundation of Henan Polytechnic University(B2008-22)
文摘A new structure containing negative refractive index dielectric layer(NRIDL) is introduced into microcavity. The properties of the new microcavity organic light-emitting devices(MOLEDs) are investigated. In the experiment, the transfer matrix method is adopted. The dependence of reflectance and transmittance on the refractive index and thickness of NRIDL are analyzed in detail. Compared with the electroluminescence spectra of non-NRIDL diodes, the line widths of the spectra of the MOLEDs are narrower and all the peaks enhance. The results show that the new structure is beneficial to improve the performance and reduce the thickness of microcavity devices.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60906022 and 60676051)the Natural Science Foundation of Tianjin,China (Grant No. 10JCYBJC01100)+2 种基金the Scientific Developing Foundation of Tianjin Education Commission, China (Grant No. 2011ZD02)the Jiangsu Provincial Natural Science Development Foundation for University, China (Grant No. 09KJB140006)the Tianjin Natural Science Council (Grant No. 10SYSYJC28100)
文摘We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode (OLED) by using the charge control layers (CCLs) based on Alq3 . The CCLs that are inserted into the emitting layers (EMLs) could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2 , which is about 2.19 times higher than that of the control device (CD) without the CCL, and the maximal luminance is 19.660 cd/m2 at 12V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.
基金Project supported by the Doctoral Foundation of the Ministry of Education of China (Grant No. 20100171110025)the State Key Laboratory of Optoelectronic Materials and Technologies,China (Grant No. 2010-RC-3-1)the Fundamental Research Funds for the Central Universities,China (Grant No. 09lgpy25)
文摘A 10-nm-thick molybdenum tri-oxide(MoO3) thin film was used as the interconnector layer in tandem organic lightemitting devices(OLEDs).The tandem OLEDs with two identical emissive units consisting of N,N-bis(naphthalen-1-yl)N,N-bis(phenyl)-benzidine(NPB) /tris(8-hydroxyquinoline) aluminum(Alq3) exhibited current efficiency-current density characteristics superior to the conventional single-unit devices.At 20 mA/cm2,the current efficiency of the tandem OLEDs using the interconnector layers of MoO3 thin film was about 4.0 cd/A,which is about twice that of the corresponding conventional single-unit device(1.8cd/A).The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200cd/m2.The experimental results demonstrated that a MoO3 thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs.Such an interconnector layer can be easily fabricated by simple thermal evaporation,greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers.A possible explanation was proposed for the carrier generation of the MoO3 interconnector layer.
文摘SiO2Al2O3 double dielectric stack layer was deposited on the surface of the GaN-based light-emitting diode (LED). The double dielectric stack layer enhances both the electrical characteristics and the optical output power of the LED because the first Al2O3 layer plays a role of effectively passivating the p-GaN surface and the second lower index SiO2 layer increases the critical angle of the light emitted from the LED surface. In addition, the effect of the Fresnel reflection is also responsible for the enhancement in output power of the double dielectric passivated LED. The leakage current of the LED passivated with Al2O3 layer was -3.46 × 10-11 A at -5 V, at least two and three orders lower in magnitude compared to that passivated with SiO2 layer (-7.14 × 10-9 A) and that of non-passivated LED (-1.9 × 10-8 A), respectively, which indicates that the Al2O3 layer is very effective in passivating the exposed GaN surface after dry etch and hence reduces nonradiative recombination as well as reabsorption of the emitted light near the etched surface.
文摘Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by 'rebuilding' cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination. In the meantime, we recapture the findings from thesearch for suitable OLED packaging materials, in particular polymer composites, which provide both heat dissipation andmoisture resistance, in addition to electrical insulation.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60906022 and 60876046)the Tianjin Natural Science Foundation,China (Grant No. 10JCYBJC01100)
文摘We fabricate a kind of novel efficient blue fluorescent organic light emitting device(OLED) based on p-n heterojunctions composed of hole transporting layer(HTL) N,N '-bis(naphthalen-1-yl)-N,N '-bis(phenyl)-benzidine(NPB) and electron transporting layer(ETL) 4,7-diphnenyl-1,10-phenanthroline(BPhen),into which a new blue material,DNCA(a derivation of N 6,N 6,N 12,N 12-tetrap-tolylchrysene-6,12-diamine),is partially doped simultaneously,and double emitting layers are configured.With a turn-on voltage of 2.6 V at 1 cd/m 2,this type of OLED presents a maximum luminance efficiency(η max) of 8.83 cd/A at 5.818 mA/cm 2 and a maximum luminance of over 40000 cd/m 2.Meanwhile,the Commission Internationale De L'Eclairage(CIE) coordinates of this device change slightly from(0.13,0.27) to(0.13,0.23) as the driving voltage increases from 3 V to 11 V.This improvement in the electroluminescent characteristics is attributed mainly to the ideal p-n heterojunction which can confine and distribute excitons evenly on two sides of the heterojunction interface so as to improve the carrier combination rate and expand the light-emitting region.
文摘The influence of different modification methods on the surface properties of indium-tin-oxide (ITO) electrodes were investigated by measurements of chemical composition,surface roughness,sheet resistance,contact angle and surface free energy.Experimental results demonstrate that oxygen plasma treatment more effectively optimizes the surface properties of ITO electrodes compared with the other treatments.Furthermore,the polymer light-emitting electrochemical cells (PLECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized.It is found that oxygen plasma treatment on the ITO electrode enhances injection current,luminance and efficiency,thereby improves the device characteristics of the PLECs.
基金Fund of Ministry of Education of China (20090172120012)the National Basic Research Program of Chima (2009CB623602)+4 种基金the National Natural Science Foundation of China (60906032)the Fundamental Research Funds for the Central Universities for the financial support. Wong W.-Y. thanks the Hong Kong Research Grants Council (HKBU202709)the University Grants Committee of HKSAR,China (AoE/P-03/08)Hong Kong Baptist University (FRG2/08-09/111)the Croucher Foundation for the Croucher Senior Research Fellowship
文摘Efficient white-polymer-light-emitting devices (WPLEDs) have been fabricated with a single emitting layer containing a hole-transporting host polymer,poly(N-vinylcarbzole),and an electron-transporting auxiliary,1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]-phenylene,codoped with two phosphorescent dyes:Iridium(III)bis (2-(4,6-difluorophenyl)-pyridinato-N,C2') picolinate (FIrpic) and home-made Ir-G2 for blue and red emission,respectively.With the structure of ITO/PEDOT:PSS 4083(40 nm)/emission layer(80 nm)/Ba(4 nm)/Al(120 nm),the device showed a maximal luminous efficiency (LE) of 13.5 cd A-1(corresponding to an external quantum efficiency (EQE) of 6.8%),and a peak power efficiency (PE) of 6.5 lm W-1 at 6.0 V.Meanwhile,the device exhibited pure white emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.34,0.35) at a current density of 12 mA cm-2,which is very close to the equi-energy white point with CIE coordinates of (0.33,0.33).The device performance can be further optimized when more balanced hole/electron injection is achieved by incorporating a lower conducting type anode buffer layer (PEDOT:PSS) and incorporating poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorenene)-alt-2,7-(9,9-dioctyfluorene)] (PFN) as an electron injection layer at the cathode.The optimized device showed an LE of 24.6 cd A-1 (with an EQE of 14.1%),while the peak power efficiency reached 12.66 lm W-1.Moreover,the WPLEDs showed good electroluminescence (EL) stability over a wide range of operating current density and luminance.
基金supported by the National Natural Science Foundation of China (21125419, 50990065, 51010003, 51073058, and 20904011)National Research Project (2009CB623601 and 2009CB930604)
文摘A series of alkali metal salts doped pluronic block copolymer F127 were used as electron injection/transport layers (ETLs) for polymer light-emitting diodes with poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene] (P-PPV) as the emission layer. It was found that the electron transport capability of F127 can be effectively enhanced by doping with alkali metal salts. By using Li2CO3 (15%) doped F127 as ETL, the resulting device exhibited improved performance with a maximum luminous efficiency (LE) of 13.59 cd/A and a maximum brightness of 5529 cd/m2, while the device with undoped F127 as ETL only showed a maximum LE of 8.78 cd/A and a maximum brightness of 2952 cd/m2. The effects of the doping concentration, cations and anions of the alkali metal salts on the performance of the resulting devices were investigated. It was found that most of the alkali metal salt dopants can dramatically enhance the electron transport capability of F127 ETL and the performance of the resulting devices was greatly improved.