A novel device structure for thermally activated delayed fluorescence(TADF)top emission organic light-emitting diodes(TEOLEDs)that improves the viewing angle characteristics and reduces the efficiency roll-off is pres...A novel device structure for thermally activated delayed fluorescence(TADF)top emission organic light-emitting diodes(TEOLEDs)that improves the viewing angle characteristics and reduces the efficiency roll-off is presented.Furthermore,we describe the design and fabrication of a cavity-suppressing electrode(CSE),Ag(12 nm)/WO_(3)(65 nm)/Ag(12 nm)that can be used as a transparent cathode.While the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency(EQE)and improved angular dependency than the device fabricated using the microcavity-based Ag electrode,it suffers from low color purity and severe efficiency roll-off.These drawbacks can be reduced by using an optimized multi-quantum well emissive layer(MQW EML).The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE(18.05%),high color purity(full width at half maximum~59 nm),reduced efficiency roll-off(~46%at 1000 cd m^(−2)),and low angular dependence.These improvements can be attributed to the synergistic effect of the CSE and MQW EML.An optimized transparent CSE improves charge injection and light outcoupling with low angular dependence,and the MQW EML effectively confines charges and excitons,thereby improving the color purity and EQE significantly.The proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.展开更多
The broad luminescence spectrum of a thermally activated delayed fluorescence(TADF)organic light-emitting diode(OLED)is a critical issue to overcome for its application in high-color-purity displays.Herein,a novel dev...The broad luminescence spectrum of a thermally activated delayed fluorescence(TADF)organic light-emitting diode(OLED)is a critical issue to overcome for its application in high-color-purity displays.Herein,a novel device structure that utilizes the first-order microcavity optical mode with a high radiance intensity is demonstrated to solve this problem by considering the charge transport properties through the analysis of hole-only and electron-only devices.In addition,by tuning the optical interference near the semitransparent top cathode layers consisting of thin silver and organic capping layers,light extraction is increased by nearly 2 times compared to the device without a capping layer.Consequently,the optimized blue TADF top-emission OLED exhibits much lower full width at half-maximum,higher maximum current efficiency,and external quantum efficiency compared to the device before optimization.This approach is expected to provide a simple but effective way to further enhance the spectral purity of the conventional TADF-based OLEDs.展开更多
The development of artificial photosensitive synapses with high sensitivity and biomimetic properties that combine innovative concepts and neuromorphic architectures is crucial to achieving highly integrated and flexi...The development of artificial photosensitive synapses with high sensitivity and biomimetic properties that combine innovative concepts and neuromorphic architectures is crucial to achieving highly integrated and flexible intelligent visual systems.Recently,graphene heterostructure-based photosensitive synaptic transistors have been extensively studied for this purpose.However,compared to traditional transistors,vertical structure thin film transistors(VTFTs)with ultra-short channels and advantages,such as high integration,have yet to be investigated in photosensitive synapses.Here,we report an ultra-thin VTFT featuring a graphene/W_(x)Se_(x-1)van der Waals heterostructure that combines photonic and neuromorphic elements.We demonstrate a VTFT in which the channel layer is formed by covalently bonded W_(x)Se_(x-1)nanomaterials produced by introducing Se atoms on the surface of a tungsten metal thin film deposited via radio-frequency sputtering.This structure successfully simulated the main synaptic function,exhib-ited photosensitive synaptic responses to ultraviolet(λ=365 nm)light,and demonstrated highly reliable electrical performance.Furthermore,the incorporation of gold nanoparticles changed the photosensitive synaptic response properties of the graphene/W_(x)Se_(x-1)heterostructure from excitatory to inhibitory,show-ing a responsivity of about∼14 A W-1,which was attributed to the heterojunction interface resonant effects and efficient charge transfer induced by localized surface plasmons.This further enabled optical artificial synaptic applications while operating with low voltage spikes and low light intensity.This work provides a novel strategy for integrating and developing biological and nano-electronic systems.展开更多
基金supported by a National Research Foundation of Korea(NRF)grant funded by the Korean government under Grant No.2016R1A3B1908249。
文摘A novel device structure for thermally activated delayed fluorescence(TADF)top emission organic light-emitting diodes(TEOLEDs)that improves the viewing angle characteristics and reduces the efficiency roll-off is presented.Furthermore,we describe the design and fabrication of a cavity-suppressing electrode(CSE),Ag(12 nm)/WO_(3)(65 nm)/Ag(12 nm)that can be used as a transparent cathode.While the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency(EQE)and improved angular dependency than the device fabricated using the microcavity-based Ag electrode,it suffers from low color purity and severe efficiency roll-off.These drawbacks can be reduced by using an optimized multi-quantum well emissive layer(MQW EML).The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE(18.05%),high color purity(full width at half maximum~59 nm),reduced efficiency roll-off(~46%at 1000 cd m^(−2)),and low angular dependence.These improvements can be attributed to the synergistic effect of the CSE and MQW EML.An optimized transparent CSE improves charge injection and light outcoupling with low angular dependence,and the MQW EML effectively confines charges and excitons,thereby improving the color purity and EQE significantly.The proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.
基金National Research Foundation of Korea(2016R1A3B1908249)。
文摘The broad luminescence spectrum of a thermally activated delayed fluorescence(TADF)organic light-emitting diode(OLED)is a critical issue to overcome for its application in high-color-purity displays.Herein,a novel device structure that utilizes the first-order microcavity optical mode with a high radiance intensity is demonstrated to solve this problem by considering the charge transport properties through the analysis of hole-only and electron-only devices.In addition,by tuning the optical interference near the semitransparent top cathode layers consisting of thin silver and organic capping layers,light extraction is increased by nearly 2 times compared to the device without a capping layer.Consequently,the optimized blue TADF top-emission OLED exhibits much lower full width at half-maximum,higher maximum current efficiency,and external quantum efficiency compared to the device before optimization.This approach is expected to provide a simple but effective way to further enhance the spectral purity of the conventional TADF-based OLEDs.
基金supported by the National Research Foundation of Korea,funded by the Korean government(Nos.2016R1A3B1908249 and 2020R1A2C3013480).
文摘The development of artificial photosensitive synapses with high sensitivity and biomimetic properties that combine innovative concepts and neuromorphic architectures is crucial to achieving highly integrated and flexible intelligent visual systems.Recently,graphene heterostructure-based photosensitive synaptic transistors have been extensively studied for this purpose.However,compared to traditional transistors,vertical structure thin film transistors(VTFTs)with ultra-short channels and advantages,such as high integration,have yet to be investigated in photosensitive synapses.Here,we report an ultra-thin VTFT featuring a graphene/W_(x)Se_(x-1)van der Waals heterostructure that combines photonic and neuromorphic elements.We demonstrate a VTFT in which the channel layer is formed by covalently bonded W_(x)Se_(x-1)nanomaterials produced by introducing Se atoms on the surface of a tungsten metal thin film deposited via radio-frequency sputtering.This structure successfully simulated the main synaptic function,exhib-ited photosensitive synaptic responses to ultraviolet(λ=365 nm)light,and demonstrated highly reliable electrical performance.Furthermore,the incorporation of gold nanoparticles changed the photosensitive synaptic response properties of the graphene/W_(x)Se_(x-1)heterostructure from excitatory to inhibitory,show-ing a responsivity of about∼14 A W-1,which was attributed to the heterojunction interface resonant effects and efficient charge transfer induced by localized surface plasmons.This further enabled optical artificial synaptic applications while operating with low voltage spikes and low light intensity.This work provides a novel strategy for integrating and developing biological and nano-electronic systems.