
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Authors: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Jaeho Lee Tae-Hee Han Min-Ho Park Dae Yool Jung Jeongmin Seo Hong-Kyu Seo Hyunsu Cho Eunhye Kim Jin Chung Sung-Yool Choi Taek-Soo Kim Tae-Woo Lee Seunghyup Yoo Abstract Iigraphene-based organic light-emitting diodes (OLEDs) zikhala zabonakala njengombane obalulekileyo kuboniso ezizukulwana ezizayo kunye nokukhanyisa, ikakhulu ngenxa yedinga labo lemithombo yokukhanya enokubhetyebhetsheka kakhulu. Nangona kunjalo, ukusebenza kwazo kube, ngcono, kufana nezo zemveli, i-indium tin oxide-based counterparts. Sikunika isicwangciso seshawu esilungeleleneyo esisekelwe kwi-synergetic interplay ye-high-index TiO2 imiba kunye ne-low-index hole-injection layers ezibeka iigraphene electrodes, eziphumela kwisimo esilungeleleneyo apho ukwanda kwe-cavity resonance kugqithisiwe ngelixa ilahleko kwi-surface plasmon polariton incitshisiwe. Indlela ecetywayo iphumela kwi-OLEDs ezibonisa i-ultrahigh external quantum efficiency ye-40.8 kunye ne-62.1% (64.7 kunye ne-103% kunye ne-half-ball lens) kwizixhobo ezipheleleyo kunye nezininzi, ngokulandelanayo. I-OLEDs eyenziwe ngeepolima kunye nezi shawu inokubhetyebhetsheka rhoqo kwi-radius ye-2.3 mm, ngokuyinxenye ngenxa ye-TiO2 imiba enokumelana ne-flexural strain ukuya kuthi ga kwi-4% nge-crack-deflection toughening. Isingeniso Izibonelelo ze-form-factor ezifana nokubhetyebhetsheka kunye nokunwebeka ziye zakhokelela i-organic light-emitting diodes (OLEDs) ingqalelo enkulu ekusetyenzisweni kwezixhobo ezivelayo ezifana ne-wearable, roll-type okanye foldable displays ezifuna ukuhamba, ukuhamba kunye/okanye ukwandiswa , . Ukuzalisekiswa ngokupheleleyo kwesi sixhobo, nangona kunjalo, akulula kwaye kufuna umzamo omkhulu kwiinkalo ezahlukeneyo ezifana nophuhliso lwezicelo ze-thin-film transistor ezinobushushu obusezantsi kunye/okanye ukugquma okubhetyebhetshekayo . Elinye icala elibalulekileyo ekufuneka licingelwe kuboniso olubhetyebhetshekayo kakhulu kukufumana ii-transparent electrodes (TEs) ezinokuthatha indawo ii-ITO electrodes, eziqhele ukubandezeleka kukubhetyebhetsheka okungagungqiyo kunye neengxaki zeendleko ezinokwenzeka ezinxulumene neemfuno eziphezulu kunye/okanye ukubonelelwa okungazinzanga . Ngokubhekisele koku, iindidi ezininzi zee-transparent electrodes ezibhetyebhetshekayo ezifana ne-metal nanowires, izinto ezinje nge-carbon (umzekelo, i-carbon nanotubes okanye i-graphene) kunye ne-metal grids ezidibene nezinye iintlobo zee-TEs ziye zacetywa kwi-OLEDs , , , , , . Phakathi kwazo, i-graphene—umkhiqizo we-atomically thin we-sp2-hybridized carbon atoms—uye wathathelwa ingqalelo njengento ethembisayo kuba ukudibanisa okuyimpawu zayo ezikhethekileyo nobukhulu bayo kwezembalelwano kulindeleke ukuba kuvumele i-transparent electrodes ezilunge ngendlela efanelekileyo ezinokuba ne-low okanye engenayo i-optical haze, i-smooth surface topology ethintela ukudayibha okubangelwa kukungalingani kunye nokonakala, i-high transmittance, i-low sheet resistance kunye nenqanaba eliphezulu lokubhetyebhetsheka konke ngexesha elinye , . Ukulungiswa ngokulula kwe-graphene esemgangathweni kwi-large-scale plastic substrates kuye kwabonakala kutshanje kwi-transparent electrodes ezineendlela zokwenziwa kwemveliso ezininzi ezihambelana nayo ngamashishini, zibonisa ukusebenza kwazo kwezinto eziphathekayo , . I-single-layer graphene (SLG) kunye ne-multi-layer graphene (MLG) zombini zibonise ukusebenza okwaneleyo kwi-TEs kwi-OLEDs , . Ngokukodwa, i-OLEDs ezisebenza kakuhle nge-graphene ziye zanikezwa uncedo lwee-hole injection layers (HILs) ezisetyenziselwa ukoyisa umsebenzi wabo we-work function ongaphantsi, owaziwa ngokuba malunga ne-4.5 eV. Ezi zicelo zokutofeka zibandakanya ii-conducting polymers ezineempawu ze-electronic gradient ezibizwa ngokuba yi-self-organized gradient HIL (GraHIL) , kunye nee-thin MoO3 buffer layers ezidibene ii-conducting polymers ye-poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) . Nangona kunjalo, ukusebenza kwamandla kunye ne-external quantum efficiency (EQE) yezi ze-state-of-the-art graphene-based OLEDs zazisenje ngendlela efanayo nezo ze-ITO-based OLEDs, ngaphandle kokuba i-bulky hemispherical lens yasetshenziswa ukwandisa i-outcoupling . Ukufumana ukusebenza okuphezulu kangangoko kubalulekile kwiziboniso ezibhetyebhetshekayo ezisetyenziswa kwiimicimbi eziphathwayo kakhulu okanye ezinokunxitywa, njengoko zihlala zixhomekeke kwiibhetri ezinomthamo omncinci wamandla ngenxa yeengxaki kubukhulu, ubunzima okanye ii-form factors. Oku kufuna ukuphuhliswa kwe-device architecture enokwandisa ukusebenza kwe-graphene-based OLEDs. Ingxaki ephambili kukuyila i-structure okanye indlela yokuvula amandla ayo apheleleyo ezinto zayo ngelixa ugcina izibonelelo zegraphene kwi-form factors kangangoko kunokwenzeka. 1 2 3 4 4 5 6 7 8 9 10 11 11 12 13 14 13 14 14 Ngale njongo, sikhangela isicwangciso seshawu esilula esisekelwe kwi-high-index TiO2 imiba kunye ne-low-index HILs ezibeka iigraphene electrodes. Ngomzobo we-optical othathela ingqalelo ngokupheleleyo intsebenziswano ye-synergetic phakathi kwemiba ephezulu nephantsi ekwaziyo ukulawula zombini i-cavity resonance enhancement kunye nelahleko kwi-surface plasmon polariton (SPP), ii-OLEDs ezisekelwe egraphene ezicetywayo zibonisa i-ultrahigh EQE engagqithiswanga kwabo basebenzisa i-graphene njenge-transparent electrode. Ngaphezu koko, i-resistance engaqhelekanga ephezulu ye-TiO2 kwi-flexural strain iyatyhilwa evumela ii-OLEDs zeplastiki ezingeyona kuphela ezisebenza kakuhle kodwa zikwangobhetyebhetshekayo. Iziphumo Uyilo lwe-optical lwe-OLEDs ezisebenza kakuhle nge-graphene Ukusebenza kwe-OLEDs kugqityezelwe kugqityezelwe kukugqityezelwa kwesiphumo sokukhutshwa ngaphandle esiqhele ukuba malunga ne-20% ngcono kwizixhobo ezine-isotropic emitters. Phakathi kwezixhobo ezahlukeneyo zokwandisa i-outcoupling ezicetywayo ukuza kuthi ga ngoku , indlela esekelwe kwi-microcavity resonance inezibonelelo kukuba igcina i-planar geometry ngaphandle kokusebenzisa naziphi na izakhiwo ze-micro/nano okanye izakhiwo ze-lenticular ukuze ii-OLEDs ezilapho zingabi nayo i-electrical shorts kunye nee-optical artefacts ezingafunekiyo kwisicelo sokubonisa (umzekelo, ukugruzuka, ukufiphaza njalo njalo) kodwa zinokubonisa imibala enabileyo, enesatellite emibala ebomvu (R), eluhlaza (G), eluhlaza okwesibhakabhaka (B) enokwandiswa , . Ngokuchaphazela okubuthathaka kodwa okusekho kubalulekileyo kwe-microcavity, ii-OLEDs ezisekelwe kwi-ITO nazo zinokulungiswa ukuze zisebenze ngokugqithisileyo, ngaphandle kokubangela naziphi na i-optical haze okanye ukugruzuka, ngokulula ngokulungisa ubukhulu bee-ITO layers; kwesi sixhobo, i-first-order, 3 /4 cavity design, apho   imele i-wavelength, ifunyenwa ngokuvuleka kwe-cavity mode kwisiqu se-ITO/substrate , . Kwimeko ye-ITO-free, graphene-based OLEDs, nangona kunjalo, ii-graphene electrodes azikwazi ukwenziwa zibe zide ngokwaneleyo ukulawula ubude be-cavity, nto leyo eyenza kube nzima ukwandisa ukusebenza nge-resonance effect . 15 16 17 λ λ 18 19 20 Njengendlela enye, umntu angabeka umbhalo obhityileyo onama-high refractive index ( H) ngaphantsi kwee-graphene layers njengoko kubonisiwe ku-  ngendlela efana ne-metal-free, dielectric capped thin-metal electrodes , , , . Ngenxa yokuba ukukhanya kungadlula kwi-graphene ngogungquko oluncinci lwenqanaba ngenxa yokubutyeba obuyimfuneko be-graphene electrode, i-3 /4 cavity design ingafunyanwa ngokulula, umzekelo, kunye nobude be-optical be-organic kunye nee-injection layers kunye ne-high refractive index layer zibekwe malunga ne-2 /4 kunye ne  /4, ngokulandelanayo ( ). Ngokukodwa, i-‘ /4-thick’ high-index layer iyakwenza njengombane obuthathaka, i-dielectric mirror ebonisa i-reflectance enkulu ukusuka kwi-bottom electrode assembly ( bot) yokukhanya okungena kwi-organic layers, njengoko kunokuqinisekiswa kwii-graphs ezibonisiweyo ezantsi kwe- . Oku kunika ii-OLEDs ezisekelwe egraphene amathuba okwandisa ukusebenza kwazo nge-resonance effect, nto leyo ebingayi kwenzeka ngenye indlela. Kubonisiwe ukuba  bot kunye nokwanda kwe-resonance okuhambelanayo kuyanda nge  H ( ). I-high refractive index ikwayinto elungele kakhulu ngokubhekiselele kubhetyebhetsheko kuba ubude be-optical obujoliswe kuyo ( H H) bungafunyanwa kunye nobukhulu obunqabileyo be-physical  H, kwaye kuba i-crack ebangelwa kukugoba kwe-film ethile idla ngokwenzeka kwi-onset strain ephantsi kunye nobukhulu be-physical obukhulu . I-high-index layer enempumelelo kwesi sixhobo ke ngoko kufuneka ibe ne- H engangenani kangangoko kunokwenzeka. Ngaphezu koko, kufuneka ibe yinto ebonakalayo, kwaye ngaphezu kwako konke, akufuneki yonakaliswe yinkqubo ethile yokudlulisa i-graphene. Phakathi kweengcamango ezininzi, i-sputtered TiO2 layer ibonakala kwibakala le-visible spectral range kwaye inama-high refractive index ( =2.5). Ngokungafaniyo nezinye ii-high-index layers esizizameyo, i-TiO2 layer iyatyhilwa ukuba inokumelana neekhemikhali okukwazi ukumelana neenkqubo zokudlulisa i-graphene ezisebenzisa i-solvent, njenge-acetone okanye i-isopropyl alcohol (IPA), ivumela ukwenziwa kwe-graphene electrode esemgangathweni phezulu kwayo ( ). n Fig. 1a 17 20 21 22 λ λ λ Fig. 1b λ R Fig. 1c,d R n Supplementary Fig. 1 n d d 23 n n Supplementary Fig. 2   ( ) Schematic device structure of the proposed OLEDs. ( ) Electromagnetic field intensity distribution (dashed lines) of the OLEDs under study for their respective first-order cavity design. The field-intensity distribution of the graphene-based OLED without TiO2 is also shown for comparison for the case where the thickness values of organic layers are same as the OLEDs with TiO2 but without low-index HILs. ( , ) Calculated maximum external quantum efficiency ( EQE) of graphene-based OLEDs with TiO2 under-layer as a function of TiO2 and organic layer thickness ( TiO2 and  org, respectively). Dashed lines represent contour lines for  EQE of 10, 20, 30 or 40% as indicated in the graph. ( ) Without a low-index HIL; ( ) with GraHIL as a low-index HIL. On the bottom of each case, the reflectance ( bot) from the bottom electrode assembly (TiO2/graphene/(HIL)) as a whole is presented as a function of  TiO2 for light incident from the organic layers. a b c d η d d η c d R d Kubalulekile ukuba i-micro-cavity structure enomgangatho ophezulu (umzekelo, i-second order, 5 /4 cavity) esekwe kwi-organic stack ebhityileyo ingasebenza. Kulo msebenzi, nangona kunjalo, i-first-order cavity design yeyona yasekwa kuqala kuba iphumela kwi-Purcell effect eyomeleleyo kunye nee-waveguide modes ezimbalwa kune-higher-order design, ekugqibeleni kukhokelela kwi-outcoupling efficiency kunye ne-EQE enkulu , . Iingxaki zisabakho kwi-first-order cavity design kuba indawo efanelekileyo yenqanaba lokukhutshwa ibekwe kwindawo yokuqala ye-antinode ukusuka kumbane we-organic/metal, yenze kube nzima ukunciphisa ii-SPP modes ngokudlulisa ixesha elide emitters-to-metal , . Indlela enye esetyenziselwa ukunciphisa i-SPP kukudibanisa imizila yangaphakathi eyimilo okanye i-corrugations , kodwa ukunyamezela kwi-electrical shorts kunokungahambelani nezi ndlela. Indlela esiyithathayo apha kukudibanisa umbhalo onama-low refractive index, obonakaliswe ngokunciphisa ngokufanelekileyo ii-SPP modes , . Ngokuthamsanqelayo, i-GraHIL okanye i-self-organized gradient hole-injection layer eyakhiwe kwi-PEDOT:PSS kunye ne-tetra-fluoroethylene-perfluoro-3, 6-dioxa-4-methyl-7-octenesulphonic acid copolymer (PFI), eyayicetyelwe ngaphambili ngababhalisi kwaye yabonakala isebenza kakhulu ekukhuliseni i-hole injection kwi-graphene-based OLEDs , inama-refractive index malunga ne-1.42 kwi   ye-550 nm ( ), nto leyo ephantsi kakhulu kunezo zee-organic layers eziqhelekileyo ( =1.8). Ngokudibana kwe-synergetic phakathi kwemiba ephezulu nephantsi ekwaziyo ukubeka iigraphene layers, ukwanda kwe-cavity-resonant effect kunye nokuncitshiswa kwama-SPP modes kungabenza ngaxeshanye ukuze i-EQE ingandiswa kakhulu ngaphandle kweziboniso zokukhutshwa. λ 24 25 25 26 27 28 29 13 λ Supplementary Fig. 3 n  ibonisa iziphumo zokulinganisa kwe-optical ezisekelwe kwi-advanced classical electromagnetic theory efingqwe yi-Furno  .  phezu kobude be-visible spectral range, kwaye kwi   ye-550 nm. I-formalism ithatha ingqalelo i-Purcell factor, i-dipole orientation effect, kunye nee-excitations ukuya kwi-SPP kunye nee-waveguide modes. Ukudibanisa okupheleleyo kwezi ziphumo zonke kubaluleke kakhulu kuhlalutyo oluchanekileyo kunye nolwakhiwo lolwazi njengoko ukungalingani okungaphezulu okanye okungaphantsi kunokwenzeka xa umntu esebenzisa indlela elula engayiboni enye okanye ngaphezulu kwezi ziphumo (bona  ;   kunye ne   ngemizekelo). Iziphumo zibonisa ukuba ukusetyenziswa kwe-GraHIL kuhlaziya ubuninzi obuhambelanayo phakathi kweemodeli ezahlukeneyo ukuya kwi-wave vectors encinci, ukuze amandla axhonywe kwi-SPP modes ancitshiswe kwaye iminqweno ekhatywayo yonyuswe ngakumbi ( ). Kunokubonwa nangokuphuma ku-  ukuba ukusetyenziswa kwe-TiO2 layer ngaphantsi kwe-graphene kunciphisa ngempumelelo ubungakanani bamandla axhonywe kwii-waveguided kunye nee-substrate modes ngokusebenzisa ukwanda kwe-resonance. Oku kukhokelela ekwandeneni okukhulu kokusebenza kwe-outcoupling, nangona ilahleko kwi-evanescent modes ikwaboniswa iyanda ngenxa yokudlula kwe-transverse-electric waveguided modes ukuya kwi-higher normalized in-plane wave vectors ( ). Ukudibanisa ukusetyenziswa kwe-high-index (H) TiO2 kunye ne-low-index (L) GraHIL layers, kuphumela kwisimo esilungeleleneyo apho i-resonance enhancement inkulu, kodwa ilahleko kwi-SPP/evanescent modes incitshisiwe. Ngaphezu koko, ukudibanisa kusenza isimo esifana nee-HL-stacks, ezisetyenziswa rhoqo kwi-multilayer thin-film coating , kwaye yandisa ngakumbi  bot ( ), okuvumela ukwanda okongeziweyo kwi-Fabry–Perot resonance effect. 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