Resonance‐Based Directional Light Emission from Organic Light‐Emitting Diodes: Comparing Integrated Nanopatterns and Color Conversion Waveguide Gratings

Resonance-Based Di ec ional Ligh Emission om O ganic Ligh -Emi ing Diodes: Compa ing In eg a ed Nanopa e ns and Colo Con e sion Wa eguide G a ings Janek Buhl,* Hannes Lüde , Gi a Bichmann, Tim Nol e, Ad ian Pe a u, and Ma ina Ge ken* 1. In oduc ion O ganic ligh -emi ing diodes (OLEDs) a e hin-film de ices employing o ganic semiconduc ing ma e ials o ligh gene a ion. In con as o con en ional ino ganic LEDs, OLEDs a e inhe en ly su ace emi e s o e ing a o able p ope ies such as he possibili y o ab ica e ully anspa en o flexible de i- ces. [1] In display applica ions, OLED panels a e widely used due o hei high colo con- as and wide iewing angles. [2] Mo eo e , OLEDs also hold g ea po en ial o nume - ous di e en applica ions including gene al ligh ing, op ical signage, and sensing. [3–6] The o ganic mul ilaye s ack o he OLED acili a es modifica ions o de ice p ope ies o ma ch indi idual applica ion equi e- men s. Addi ionally, solu ion-based manu- ac u ing me hods o o ganic op oelec on- ics allow o cos -e ficien de ice ab ica ion, making OLEDs a o able candida es o poin -o -need applica ions o ecyclable single-use de ices. OLED illuminan s ypically ea u e homogeneous wide-angle ligh emission sui able o la ge-a ea and indi ec ligh ing. Howe e , in o he scena ios, na ow-angle ligh emission and di ec ional illumina ion o specific a eas a e desi ed. We ha e p e- iously demons a ed a minia u ized op i- cal sensing uni o poin -o -need analysis comp ising se e al pai s o OLED ligh sou ces and o ganic pho- ode ec o s on a single subs a e. [7] Di ec ional ligh emission owa d he sensing spo s may significan ly inc ease he ligh u iliza ion a io and o e all sys em sensi i i y in he p oposed side-by-side configu a ion. [8] In con en ional sensing sys ems, addi ional componen s a e ypically used o adjus he op ical pa h and ocus ligh on o he sensing a ea. In he case o highly minia u ized senso s which do no allow o any assembly o alignmen s eps, all op ical elemen s mus be in eg a ed di ec ly in o he de ices. Mos o he s udies on di ec ional OLED emission ocus on he mally e apo a ed small molecules. While hese ma e ials usually p o ide high de ice pe o mance wi h espec o lumi- nance and e ficiency, hey also equi e acuum p ocessing, lead- ing o inc eased manu ac u ing cos s. Solu ion-based la ge-scale ab ica ion me hods, such as slo -die coa ing o inkje p in ing, in con as , may p o ide easonably a o dable o ganic op oelec- onics o disposable sensing uni s. Solu ion-p ocessed de ice s acks gene ally comp ise polyme semiconduc o s whose op ical p ope ies mus be aken in o conside a ion. A well-known app oach o ob ain angle-dependan ligh emis- sion is esonan ou coupling o quasi-guided op ical modes om J. Buhl, H. Lüde , G. Bichmann, T. Nol e, A. Pe a u, M. Ge ken Facul y o Enginee ing Kiel Uni e si y Kaise s . 2, 24143 Kiel, Ge many E-mail: [email p o ec ed]; [email p o ec ed] J. Buhl, H. Lüde , G. Bichmann, T. Nol e, A. Pe a u, M. Ge ken Kiel Nano, Su ace and In e ace Science KiNSIS Kiel Uni e si y Ch is ian-Alb ech s-Pla z 4, 24118 Kiel, Ge many The ORCID iden ifica ion numbe (s) o he au ho (s) o his a icle can be ound unde h ps://doi.o g/10.1002/adp .202200143. © 2022 The Au ho s. Ad anced Pho onics Resea ch published by Wiley- VCH GmbH. This is an open access a icle unde he e ms o he C ea i e Commons A ibu ion License, which pe mi s use, dis ibu ion and ep oduc ion in any medium, p o ided he o iginal wo k is p ope ly ci ed. DOI: 10.1002/adp .202200143 Tailo ing he angula emission pa e n o o ganic ligh -emi ing diodes (OLEDs) is a p omising app oach o inc ease de ice pe o mance in many applica ions. In minia u ized poin -o -need senso sys ems using o ganic ligh sou ces and pho ode ec o s, di ec ional illumina ion o specific sensing spo s may enhance o e all sensi i i y by imp o ed ligh u iliza ion. Pe iodically nanopa e ned wa eguides o ming pho onic c ys al slabs a e o en imes employed o ob ain di ec ional esonan ligh ou coupling om OLEDs. This wo k compa es emis- sion di ec ionali y o wo ypes o de ices u ilizing he same polyme compounds as he emissi e ma e ial: OLEDs comp ising a nanopa e ned bo om elec ode and con en ional OLEDs ea u ing a dedica ed nanopa e ned colo con e sion laye (CCL) o di ec ional ligh ou coupling. Simula ed and expe imen ally measu ed emission cha ac e is ics show ha esonan ou coupling e ec s om a sepa a e CCL a e significan ly s onge due o spa ial sepa a ion om he lossy elec ode laye s as well as high op ical con as a he wa eguide in e aces. While OLEDs wi h nanopa e ned elec odes exhibi only small de ia ions om he Lambe ian emission p ofile, he nanopa e ned CCL induces high ou coupling peaks a specific iewing angles leading o inc eased emission di ec ionali y. RESEARCH ARTICLE www.adp -jou nal.com Ad . Pho onics Res. 2023,4, 2200143 2200143 (1 o 9) © 2022 The Au ho s. Ad anced Pho onics Resea ch published by Wiley-VCH GmbH a pe iodically nanopa e ned wa eguide o ming a pho onic c ys- al slab. [9,10] Ligh p opaga es inside a slab wa eguide in he o m o guided modes. A guided mode is an elec omagne ic wa e, mos ly confined in he high-index laye , which p opaga es along he wa eguide wi hou changing i s field p ofile. Depending on he pola iza ion o he elec ic and he magne ic field wi h espec o he p opaga ion di ec ion, guided modes a e di ided in o ans e se elec ic (TE) and ans e se magne ic (TM) modes. A mode p opaga ing along he x-axis (see Figu e 1 o an illus- a ion o he g a ing wa eguide s uc u e and he co esponding coo dina e sys em) is cha ac e ized by i s wa e ec o k¼kmodeex o , equi alen ly, by i s e ec i e e ac i e index ne ¼kmode k0 (1) whe e k0¼2π=λ0is he ee-space wa e numbe . Fo all guided modes, ne is la ge han he e ac i e indices o he su ound- ing media. Fo any wa e in ee space, he in-plane componen o i s wa e ec o is gi en as kx¼k0sinðϑÞ<k0<kmode (2) whe e ϑis he angle o he p opaga ion di ec ion wi h espec o he slab wa eguide’s su ace no mal. The e o e, guided modes canno couple o inciden o ou going plane wa es because he necessa y momen um conse a ion canno be ulfilled. The in oduc ion o a pe iodic e ac i e index modula ion along he x-axis, c ea ing a pho onic c ys al slab, leads o B agg sca e - ing o he guided modes. As long as he e ac i e index modu- la ion is su ficien ly weak, he in-plane wa enumbe a e sca e ing can be w i en as k0 mode ¼kmode þm⋅G,m∈ℤ(3) whe e G¼2π=Λis he ecip ocal g a ing ec o . I k0 mode alls in o he ligh cone jk0 modej<k0 o any m∈ℤ, he sca e ed mode will couple o he a field wi h an ou -coupling angle sinðϑÞ¼k0 mode=k0. Typically, m¼1, yielding [11] sin ϑðÞ¼ne λ0 Λ(4) Consequen ly, he g a ing in he wa eguide u ns a guided in o a quasi-guided mode ha leaks ene gy in o he a field. Fo each op ical mode, condi ion (4) is uly sa isfied o one spe- cific wa eleng h a a fixed iewing angle ϑ, esul ing in esonan ou -coupling peaks ha ollow he mode’s dispe sion ela ion. In eg a ed pho onic c ys al s uc u es in OLEDs may lead o enhanced ou coupling o wa eguided modes, imp o ing de ice e ficiency and modi ying angula emission cha ac e is ics. [12–14] They a e commonly ab ica ed by ei he deposi ing he bo om elec ode on o a nanopa e ned laye o pa e ning he elec ode i sel . [15] The pho onic c ys al slab is consequen ly o med by he en i e laye s ack. Significan changes o he emission cha ac e - is ics o OLEDs ha e been achie ed wi h his app oach. [16–18] Howe e , ligh di ec ionali y is usually limi ed due o he high abso p ion o he elec ode laye s educing he p opaga ion leng h in he wa eguide. Addi ionally, many o he o ganic poly- me semiconduc o s used in solu ion-p ocessed OLED s acks exhibi high e ac i e indices close o ha o indium in oxide (ITO), which is he mos commonly used elec ode ma e ial. Since he esul ing op ical con as is compa a i ely low, i is e en mo e di ficul o achie e di ec ional emission om de ices com- p ising high-index polyme ma e ials. Highly di ec ional ou coupling o subs a e modes can also be ob ained by placing a di ac i e op ical elemen adjacen o he OLED while blocking nondi ec ional di ec emission. [19] Al hough his app oach allows confinemen o he emissi e ligh o a e y na ow cone angle, only a small ac ion o he o al OLED ligh is u ilized, making i un a o able o poin -o -need sensing applica ions. As an al e na i e app oach, we p opose he applica ion o a nanopa e ned fluo escen wa eguide in Me al elec ode O ganic s ack ITO Subs a e Fluo escen wa eguide Type A Type B (a) (b) 0 20 40 60 80 nm 1 μm 0 20 40 60 80 nm 1 μm 1 μm 1 μm (c) x x z z (d) 0 100 0 0.2 0.4 0.6 0.8 1 362 nm / nm / μm 0 100 60 nm Figu e 1. a) Schema ic ep esen a ion o he de ice s uc u es. De ice ype A: o ganic ligh -emi ing diode (OLED) wi h a nanopa e ned indium in oxide (ITO) bo om-elec ode. De ice ype B: OLED wi h a nanopa - e ned fluo escen wa eguide laye . b) The deposi ed polyme laye leads o a enua ion o he in eg a ed nanopa e n, as appa en in he su ace p ofiles o he ype B de ice measu ed by a omic o ce mic oscopy (AFM). c) shows scanning elec on mic oscopy (SEM) images o he nanopa e ned ITO elec ode ( op) and he deposi ed o ganic laye s ack (bo om) in ype A de ices, while d) shows AFM images o he nanopa - e ned imp in esis ( op) and he fluo escen wa eguide (bo om). In bo h de ice ypes, he pe iodici y o he one-dimensional nanog a ing s uc u e is p ese ed h oughou he laye sequence. www.ad ancedsciencenews.com www.adp -jou nal.com Ad . Pho onics Res. 2023,4, 2200143 2200143 (2 o 9) © 2022 The Au ho s. Ad anced Pho onics Resea ch published by Wiley-VCH GmbH 26999293, 2023, 2, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adp .202200143 by Uni e si a sbiblio hek Kiel, Wiley Online Lib a y on [20/08/2023]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License combina ion wi h a con en ional OLED. In his de ice s uc u e, he fluo escen laye ac s as a colo con e sion laye (CCL) ee- mi ing ligh in o he wa eguide. Spa ial sepa a ion om he yp- ically lossy elec ode ma e ials ensu es a high-quali y ac o leading o na ow-angle emission o he fluo escen ligh . In his wo k, we compa e ligh emission cha ac e is ics om wo ypes o di ec ional OLEDs, namely OLEDs comp is- ing a pe iodic nanopa e n e ched in o he ITO elec ode (OLED ype A) and con en ional OLEDs ea u ing a pe iodi- cally nanopa e ned fluo escen wa eguide laye deposi ed on he subs a e backside (OLED ype B), by simula ion and expe imen al me hods. Figu e 1 shows he wo de ice s uc u es unde in es iga ion including scanning elec on mic oscopy (SEM) and a omic o ce mic oscopy (AFM) images o he ab ica ed samples. 2. De ice Design and Fab ica ion We used he same fluo escen polyme s as he emissi e laye in OLEDs o ype A and as he fluo escen wa eguide laye in OLEDs o ype B so as o be able o di ec ly compa e he emission cha - ac e is ics o he di e en OLED ypes. Specific combina ions o emission wa eleng h and angle can be ob ained by he app op ia e choice o polyme emission spec um and nanopa e n design. The polyme s chosen in his s udy a e Poly(9,9-dioc ylfluo ene- al -benzo hiadiazole) (F8BT) and Poly[2-me hoxy-5-(20-e hylhexy- loxy)-1,4-phenylene inylene] (MEH-PPV). The complex e ac i e indices o he polyme hin films as well as hei pho olumines- cence (PL) emission spec a a e shown in Figu e 2. The wo polyme compounds we e chosen expec ing a consid- e able di e ence be ween g een (F8BT) and o ange/ ed (MEH- PPV) emission. [20] The F8BT ma e ial ba ch used o his s udy, howe e , exhibi ed o ange ligh emission, esul ing in simila emission spec a o bo h compounds. While a blend o F8BT and PFO (Poly(9,9-di-n-oc ylfluo enyl-2,7-diyl)), which is com- monly used o polyme OLEDs, [21] yielded he expec ed g een emission colo , he abso p ion spec um o PFO was no sui able o ype B de ices. Elec oluminescence (EL) spec a o he OLED de ices may addi ionally show sligh de ia ions om he PL spec- a o he isola ed polyme laye s due o he op ical ca i y o med by he elec ode laye s. Resonan ligh coupling in pho onic c ys al s uc u es is a well-unde s ood phenomenon. The in ensi y and shape o he esonance e ec s depend on he op ical p ope ies o he wa eguide i sel as well as he pe iodic nanopa e n. [22] In ype A OLEDs, he wa eguide is o med by he ITO bo om elec ode plus he o ganic laye s ack and is bounded by he me allic op elec ode. In ype B OLEDs, he wa eguide only comp ises he fluo escen polyme laye . Isola ed compa ison o di e en wa eguide configu a ions is only possible i he geome ic pa ame e s o he in eg a ed nanopa e ns a e e ec i ely iden- ical. To achie e high s uc u al con o mi y, we employed he UV nanoimp in li hog aphy p ocess de ailed in e . [23] u iliz- ing a single mas e s amp holding a 1D g a ing wi h a pe iod leng h o 370 nm and a g a ing dep h o 60 nm o nanopa e n gene a ion on all samples. Fo he imp in ing s eps, seconda y PDMS (polydime hylsiloxane) s amps we e ab ica ed, which ea u ed a sligh ly educed pe iod leng h o 362 nm due o he he mal sh inkage o he silicone. The esul ing, i ually iden ical, nanog a ings we e subsequen ly used as empla es o pa e ning o he wa eguide ma e ials. The exac ag eemen o he final nanopa e ns in bo h de ice ypes, howe e , was no ob ainable as he espec i e nanopa e n placemen equi ed di e en ab ica ion app oaches. Nanopa e ned ITO laye s o OLEDs o ype A we e ab ica ed by ion beam e ching using he pa e ned nanoimp in esis as an e ching empla e. P ocess de ails and pa ame e s we e he same as desc ibed in e . [24] The g a ing dep h o he nanopa e n in he elec ode laye is educed o 50 nm owing o di e ences in he e ching a es o he imp in esis and ITO. The g a ing pe iod and he gene al pa e n shape, on he o he hand, a e p e- se ed h oughou he e ching p ocess. The o ganic laye s ack consis ing o poly(3,4-e hylenedioxy hiophene) polys y ene sul o- na e (PEDOT:PSS, 50 nm) and ei he F8BT o MEH-PPV (70 nm) was subsequen ly deposi ed on o he nanopa e ned ITO elec ode by spin-coa ing. Finally, a 1 nm hick laye o LiF and a 150 nm Al ca hode we e he mally e apo a ed. While OLEDs wi h nanopa e ned CCLs aiming a whi e ligh emission ha e al eady been epo ed, hey ypically show low di ec- ionali y due o he esidual OLED emission. [25] To u ilize mos o he exci a ion ligh and supp ess nondi ec ional blue backg ound emission in ype B OLEDs, we employed highly abso ben fluo es- cen laye s wi h a hickness be ween 200 and 300 nm, which is sig- nifican ly highe han in he o ganic s ack o ype A de ices. We used a blue OLED comp ising he emissi e ma e ial 2,3,5,6- Te akis(3,6-di- e -bu yl-9 H-ca bazol-9-yl)benzoni ile (4TCzBN) 0 0.5 1 1.5 2 2.5 400 500 600 700 0 0.5 1 1.5 2 2.5 (a) F8BT MEH-PPV 0 0.5 1 400 500 600 700 (a) (b) In ensi y (no m.) F8BT MEH-PPV 4TCzBN (OLED) Figu e 2. a) Re ac i e indices measu ed by whi e-ligh ellipsome y. b) Emission spec a o F8BT and MEH-PPV compa ed o he emission spec um o he exci a ion OLED. E ficien exci a ion o he fluo escen films is expec ed because o good ag eemen be ween he ex inc ion coe - ficien kand he emission peak o he blue OLED. www.ad ancedsciencenews.com www.adp -jou nal.com Ad . Pho onics Res. 2023,4, 2200143 2200143 (3 o 9) © 2022 The Au ho s. Ad anced Pho onics Resea ch published by Wiley-VCH GmbH 26999293, 2023, 2, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adp .202200143 by Uni e si a sbiblio hek Kiel, Wiley Online Lib a y on [20/08/2023]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License as he exci a ion sou ce, ma ching he abso p ion spec a o F8BT and MEH-PPV. Blue exci a ion OLEDs o de ices o ype B we e ab ica ed by he mal e apo a ion on glass subs a es employing he ollowing de ice s ack: ITO (140 nm) j1,4,5,8,9, 11-Hexaaza iphenylenehexaca boni ile (HATCN, 5 nm) j 1,1-Bis[(di-4- olylamino)phenyl]cyclohexane (TAPC, 35 nm) j 1,3-Bis(N-ca bazolyl)benzene (mCP) doped wi h 4TCzBN (20%, 25 nm)jDiphenyl[4-( iphenylsilyl)phenyl]phosphine oxide (TSPO1, 5 nm) j2,20,200-(1,3,5-Benzine iyl)- is (1-phenyl-1-H-benzimidazole) (TPBi, 30 nm) jLiF (1 nm) j Al (150 nm). OLED ab ica ion was ollowed by he o ma ion o he nanopa e ned CCL. Fo his pu pose, a nanog a ing empla e was deposi ed on he backside o he OLED subs a e by UV nanoimp in li hog aphy, as men ioned ea lie . This bo om laye was subsequen ly co e ed by spin-coa ing ei he F8BT o MEH-PPV om hei espec i e solu ions in oluene, o ming a nanopa e ned wa eguide. The nanog a ings in eg a ed in o he di e en wa eguide con- figu a ions a e iden ical excep o a 10 nm di e ence in g a ing heigh . We belie e his de ia ion o be negligible because he g a ing heigh is expec ed o mainly a ec he spec al wid h o he esonance e ec . Fu he disc epancy be ween he pho- onic c ys al slabs may a ise due o he deposi ion o he wa e- guide ma e ial. In bo h ype A and ype B de ices, polyme laye s a e spin-coa ed on o he nanog a ing, leading o he filling o he nanopa e n. [26] As confi med by he AFM measu emen shown in Figu e 1, he op side o he polyme laye exhibi s an a enu- a ed g a ing s uc u e wi h educed g a ing heigh and ounded ea u e shapes. The g a ing a enua ion e ec is an icipa ed o be less p onounced in ype A de ices, since he o ganic laye s ack hickness is conside ably lowe han he wa eguide hickness in ype B de ices. 3. Simula ion Resul s We simula ed he adia ion pa e ns o bo h OLED ypes using he fini e-di e ence ime-domain me hod (Ansys Lume ical FDTD) in combina ion wi h a ecip oci y-based a -field calcula- ion me hod. [27,28] Following his app oach, he s uc u e is exci ed by plane wa es ha ep esen he inciden field o dis an dipoles in he a field. The esul ing fields a e measu ed in he emissi e laye . By means o he ecip oci y p inciple, he esul s o he ecip ocal si ua ion, i.e., dipole emi e s in he ac i e a ea and field moni o s in he a field, can be calcula ed. We employed Lume ical’s BFAST plane wa e sou ce o accu a e b oadband plane wa e injec ion a all injec ion angles. [29] Because he nanopa e ns a e 1D, i is su ficien o simula e 2D uni cells o he pe iodically pa e ned de ices. The simula ed s uc u es a e depic ed in Figu e 3. In all cases, he simula ion egion is bounded by pe ec elec- ic conduc o s (PEC) a he op and bo om and BFAST bound- a y condi ions a he le and igh bounda y. Pe ec ly ma ched laye s (PMLs) a e used o emula e eflexionless adia ion in o he a field. We used he measu ed e ac i e indices shown in Figu e 3 o MEH-PPV and F8BT and da a om he li e a u e o he emaining OLED ma e ials. [30–35] To s abilize he simu- la ion in cases o ul a high-Q esonances in he anspa en windows (λ>600 nm o MEH-PPV and λ>550 nm o F8BT), whe e k¼0, we added a small abso p ion k¼0.003 o he measu ed complex e ac i e indices. No e ha eal de ices will always su e om addi ional losses due o incohe en sca - e ing a geome ic i egula i ies, which a e o he wise no included in he simula ion. Fo ype A s uc u es, he en i e OLED s ack con aining he emissi e polyme laye is conside ed in he simula ion. Fo ype B s uc u es, he fluo escen laye is assumed o be exci ed homogeneously by he blue OLED. The e o e, he exci a ion is no included in he simula ion o ype B de ices. Ins ead, we simula ed only he emission om dipoles in he nanopa e ned fluo escen wa eguide. TM modes a e expec ed o be ba ely exci ed because he dom- inan emi e dipole o ien a ion in spin-coa ed conjuga ed poly- me laye s is in plane. [36] The e o e, we simula ed only he adia ion pa e ns om emi e dipoles o ien a ed pa allel o he g a ing lines, which exci e only TE modes. In he simula ions, i is assumed ha emi ing dipoles a e homogeneously dis ib- u ed in he emission laye . To ge quan i a i ely compa able esul s, he a fields a e no malized by he emission laye a ea. The simula ion esul s a e shown in Figu e 4. S ong esonan ou coupling peaks can be seen o bo h ype B OLEDs wi h he nanopa e ned fluo escence laye , while ype A OLEDs exhibi only weak ou coupling esonances. The eso- nance quali y ac o depends mainly on he e ac i e index con- as in oduced by he nanog a ing and he op ical mode’s p opaga ion leng h inside he wa eguide. Since he espec i e emissi e ma e ials a e he same in ype A and B OLEDs, eso- nance in ensi y is di ec ly compa able. The dis inc di e ences be ween he wo de ice designs can he e o e be explained as ollows: The addi ional OLED laye s in ype A de ices (ITO, PEDOT:PSS, and Al) cause inc eased abso p ion o he quasi- guided modes, lowe ing hei p opaga ion leng h. Addi ionally, F8BT/MEH-PPV Al PML Type A Type B PML Glass ITO Ai PEDOT:PSS F8BT/MEH-PPV Glass PML 100 nm Figu e 3. Simula ed de ice s uc u es o ype A and B OLEDs. The g a ing a enua ion shown in Figu e 1 is aken in o accoun in he model. The ai and glass laye hicknesses a e no o scale. Thei hickness in he simula- ion is 1 μm o keep he pe ec ly ma ched laye s (PMLs) a a dis ance om he nea fields a ound he nanos uc u es. The plane wa e sou ces neces- sa y o he ecip oci y-based simula ion a e placed a ew mesh cells abo e he bo om PML. 2D field moni o s a e placed on he F8BT/MEH-PPV laye s. www.ad ancedsciencenews.com www.adp -jou nal.com Ad . Pho onics Res. 2023,4, 2200143 2200143 (4 o 9) © 2022 The Au ho s. Ad anced Pho onics Resea ch published by Wiley-VCH GmbH 26999293, 2023, 2, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adp .202200143 by Uni e si a sbiblio hek Kiel, Wiley Online Lib a y on [20/08/2023]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License he ini ially nanopa e ned in e ace in ype A de ices is loca ed be ween he ITO elec ode and he o ganic laye s ack con aining he high-index polyme , esul ing in a compa a i ely low e ac- i e index modula ion. The fluo escen wa eguide in ype B OLEDs, in con as , is deposi ed on he nanoimp in esis (n1.51) leading o a significan ly highe op ical con as . Consequen ly, he esonance s eng h is expec ed o be much highe in he ype B s uc u e. Fu he mo e, bo h ype B de ices show wo TE esonances (TE0and TE1) due o he highe laye hickness. The TE0mode’sfield is s ongly confined in he cen e o he high index laye , leading o weak in e ac ion wi h he g a - ing. As a esul , he TE0modes show ex emely high-quali y ac- o s (Q400 o he F8BT wa eguide and Q2000 o he MEH-PPV wa eguide), which may ende hem in isible in he expe imen . 4. Expe imen al Resul s We eco ded angle- esol ed emission spec a o he ab ica ed OLED de ices in 1° s eps using an in-house buil goniopho ome e se up. TE and TM esonance peaks we e di e en ia ed expe imen- ally by placing a linea pola iza ion fil e in on o he de ec o . Compa ison wi h he simula ed esonance posi ions yielded he co esponding quasi-guided mode o de . To allow o di ec com- pa ibili y o he esonance e ec s i espec i e o OLED e ficiency and b igh ness, we exci ed he emissi e pho onic c ys al s uc u es op ically wi h an ex e nal ligh sou ce ma ching he polyme s’ abso p ion spec a. Fo his, he en i e de ice a ea was homo- geneously illumina ed by a blue LED wi h an emission maximum a ound 455 nm (M455D3, Tho labs), which was fixed on he o a- ional s age o he goniopho ome e se up o ob ain iden ical exci- a ion s eng h o all iewing angles. The esul ing PL emission spec a o he wo de ice ypes employing F8BT and MEH-PPV as he emissi e ma e ial, espec i ely, a e depic ed in Figu e 5. Fo compa ison, emission spec a o he OLEDs in elec ical ope a ion we e also measu ed using he same goniopho ome e se up and an ex e nal sou ce measu e uni o ope a e he OLEDs a a cons an cu en densi y (see Figu e 6). The con as in esonance quali y be ween he OLED ypes obse able in he expe imen is e en mo e p onounced han sug- ges ed by he simula ion. Di e ences in esonance posi ions be ween he simula ion and expe imen can be a ibu ed o de i- a ions in he e ac i e indices and he ac ha he simula ion used iso opic ma e ial pa ame e s o simplici y. De ices o ype A exhibi ba ely ecognizable esonance e ec s which a e s ongly domina ed by nondi ec ional fluo escence emission a all iewing angles. In con as , he PL emission spec a o de ices o ype B ea u e sha p ou coupling peaks owing o he signifi- can ly highe esonance quali y ac o , as desc ibed abo e. Mo eo e , he esonance posi ion in ype B de ices is loca ed a highe wa eleng hs (compa ed o ype A de ices) due o he inc eased wa eguide laye hickness and he la ge amoun o he high-index polyme . Simila o he simula ion, a single esonan TE mode is obse able o he ype A de ices, while he ype B F8BT sample 500 550 600 650 700 -20 -10 0 10 20 Type A F8BT 500 550 600 650 700 -20 -10 0 10 20 0 0.2 0.4 0.6 0.8 1 In ensi y (no m.) (a) 500 550 600 650 700 -20 -10 0 10 20 Type B F8BT 500 550 600 650 700 -20 -10 0 10 20 0 0.5 1 1.5 2 2.5 3 In ensi y (no m.) (b) 500 550 600 650 700 -20 -10 0 10 20 Type A MEH-PPV 500 550 600 650 700 -20 -10 0 10 20 0 0.2 0.4 0.6 0.8 1 In ensi y (no m.) (c) 500 550 600 650 700 -20 -10 0 10 20 Type B MEH-PPV 500 550 600 650 700 -20 -10 0 10 20 0 0.5 1 1.5 2 2.5 3 In ensi y (no m.) (d) Figu e 4. Simula ed angle- esol ed emission cha ac e is ics o ype A and ype B de ices wi h a,b) F8BT and c,d) MEH-PPV emissi e laye s. Emission in ensi ies a e no malized globally, hus he esul s a e quan i a i ely compa able. Colo ba se ings ha e been adjus ed o be e pe cep ibili y, because esonan ou coupling e ec s a e significan ly s onge in ype B de ices ( igh side). www.ad ancedsciencenews.com www.adp -jou nal.com Ad . Pho onics Res. 2023,4, 2200143 2200143 (5 o 9) © 2022 The Au ho s. Ad anced Pho onics Resea ch published by Wiley-VCH GmbH 26999293, 2023, 2, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adp .202200143 by Uni e si a sbiblio hek Kiel, Wiley Online Lib a y on [20/08/2023]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License (b) ea u es wo TE modes (Q370 o he TE0mode and Q210 o he TE1mode). Howe e , he TE0mode in he ype B MEH-PPV sample (d), which is loca ed a ound λ670 nm a ϑ¼0∘acco ding o he simula ion and expec ed o ha e a quali y ac o in he ange o Q2000, is no isible in he expe imen . We a ibu e his de ia ion o he ex emely high-quali y ac o o he MEH-PPV wa eguide’sTE 0mode. This high Q ac o co e- sponds o a e y weak coupling o he a field (and e y low abso p ion), which equi es a long p opaga ion leng h o o m a no able ou coupling peak. Incohe en sca e ing e ec s due o s uc u al i egula i ies (c ea ing b oadband, omnidi ec ional emission) limi he mode p opaga ion and he e o e he o ma- ion o a defined ou coupling peak. Bo h wa eguides con aining F8BT allow o he o ma ion o a ela i ely weak TM mode, which is clea ly isible in he 0∘emis- sion spec a shown in Figu e 6 (λ570 nm in he ype A de ice and λ580 nm in he ype B de ice). Due o he e ac i e index aniso opy o he polyme laye , he o de o he e ec i e e ac- i e indices o TE and TM modes can di e om he al e na ing pa e n ound in iso opic slab wa eguides. TM modes a e no accoun ed o in he simula ion, as only emi e dipoles coupling in o TE modes a e conside ed. EL and PL emission cha ac e is icso hepolyme laye sin de iceso ypeAa esimila because hegene alde ices uc- u e emains unchanged. Sligh di e ences may a ise as he loca ion o he emission zone inside he hin film du ing elec- ical ope a ion is de e mined by cha ge ecombina ion. Ne e heless, significan enhancemen o esonan ou cou- pling canno be expec ed. [37] The in ensi y o he ou coupling e ec s can mos easily be assessed by compa ing emission spec a a a fixed ou coupling angle (co esponding o a e ical cu in he angle- esol ed emission spec a), as shown in Figu e 6. In acco dance wi h he angle- esol ed emission cha ac e is ics, a small TE esonance peak a λ¼580 nm is obse able o he ype A F8BT de ice exhibi ing a sligh ly sha pe p ofile in he elec oluminescence measu emen . Fo he ype A MEH-PPV de ice no esonance e ec s a e isible a ϑ¼0∘. Fluo escence emission and esonance in ensi y o ype B de i- ces a e expec ed o be iden ical o PL and EL measu emen s as he nanopa e ned CCL is op ically exci ed in bo h cases. Di e ences in he emission spec a a e due o esidual OLED emission, which educes o e all emission di ec ionali y. In com- pa ison, he F8BT wa eguide laye exhibi s a highe quali y ac o han he MEH-PPV wa eguide, appa en by he significan ly sha pe esonance peaks. Addi ionally, supp ession o nondi ec- ional OLED backg ound ligh is highe , esul ing in ligh ou coupling a ex emely na ow cone angles o specific wa e- leng hs. Al hough he MEH-PPV CCL ea u es a highe ans- mission o he OLED exci a ion ligh , emission di ec ionali y is s ill high. While he b oade shape o he esonance peak esul s in sligh ly lowe wa eleng h selec i i y, he inc ease in spec al bandwid h o he esonance enhances he o al amoun o ligh coupled in o a specific di ec ion. 500 550 600 650 700 -20 -10 0 10 20 Type A F8BT 500 550 600 650 700 -20 -10 0 10 20 0 0.2 0.4 0.6 0.8 1 In ensi y (no m.) (a) 500 550 600 650 700 -20 -10 0 10 20 Type B F8BT 500 550 600 650 700 -20 -10 0 10 20 0 0.2 0.4 0.6 0.8 1 In ensi y (no m.) (b) 500 550 600 650 700 -20 -10 0 10 20 Type A MEH-PPV 500 550 600 650 700 -20 -10 0 10 20 0 0.2 0.4 0.6 0.8 1 In ensi y (no m.) (c) 500 550 600 650 700 -20 -10 0 10 20 Type B MEH-PPV 500 550 600 650 700 -20 -10 0 10 20 0 0.2 0.4 0.6 0.8 1 In ensi y (no m.) (d) Figu e 5. Angle- esol ed PL emission spec a o he OLED de ices unde in es iga ion wi h a,b) F8BT and c,d) MEH-PPV emissi e laye s. Type A de ices (le side) show minimal esonan ou coupling e ec s while ype B de ices ( igh side) exhibi high esonance quali y. Simila o he simula ion esul s shown in Figu e 4, nondi ec ional backg ound emission is almos exclusi ely isible in ype A de ices. www.ad ancedsciencenews.com www.adp -jou nal.com Ad . Pho onics Res. 2023,4, 2200143 2200143 (6 o 9) © 2022 The Au ho s. Ad anced Pho onics Resea ch published by Wiley-VCH GmbH 26999293, 2023, 2, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adp .202200143 by Uni e si a sbiblio hek Kiel, Wiley Online Lib a y on [20/08/2023]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License Di ec ional ligh ou coupling om ou ype A de ices is significan ly lowe han epo ed o simila de ices employing di e en o ganic laye s acks. [15,38] Consequen ly, we ab ica ed en i ely he mally e apo a ed OLEDs on op o he nanopa e ned ITO elec odes o ee alua e he sui abili y o ou ab ica ion app oach. The co esponding angle-dependan emission cha ac- e is ics p esen ed in Figu e 7 show clea ly ecognizable esonan ou coupling e ec s and di ec ional ligh emission. We, he e o e, a ibu e he low esonance quali y o he pho onic c ys al s uc- u es in he solu ion-p ocessed OLEDs o he o ganic laye s ack i sel . As men ioned p e iously, he dominan e ac i e index modula ion in his de ice s uc u e usually occu s a he in e ace be ween he ITO bo om elec ode (n2) and he o ganic semiconduc ing laye s ( ypically n1.61.8). Since he polyme ma e ials used in his wo k also exhibi high e ac i e indices close o 2, he op ical con as is educed, leading o lowe eso- nance in ensi y. Type B de ices, in con as , ea u e a sepa a e nanopa e ned high-index wa eguide laye p o iding s ong e ac i e index modula ion a he in e ace be ween he fluo es- cen polyme and he imp in esis . Pola plo s o he in eg a ed emission in ensi y o bo h ypes o de ices a e depic ed in Figu e 8. Type A de ices exhibi wide-angle emission cha ac e is ics simila o he ideal Lambe ian emission pa e n. In con as , ype B de ices show dis inc de ia ions om he Lambe ian emission shape. Inc eased ligh ou coupling is obse able a iewing angles up o 30°, which is in acco dance wi h he eso- nance e ec s isible in Figu e 5. In he in es iga ed samples, ligh ou coupling is enhanced mainly in he o wa d di ec ion, i.e., pe pendicula o he subs a e su ace. Di ec ional emission in o highe iewing angles is ob ainable by al e ing he pe iod leng h o he nanopa e n o shi he esonance posi ion. In many applica ion scena ios, addi ional spec al fil e ing is in oduced due o di e en sys em componen s such as 0 0.5 1 500 600 700 Type A F8BT In ensi y (no m.) PL EL (a) TE0 TM0 0 0.5 1 500 600 700 Type B F8BT In ensi y (no m.) PL EL (b) TE1 TM0 TE0 0 0.5 1 500 600 700 Type A MEH-PPV In ensi y (no m.) PL EL (c) 0 0.5 1 500 600 700 Type B MEH-PPV In ensi y (no m.) PL EL (d) TE1 Figu e 6. Compa ison be ween emission spec a o he in es iga ed OLED de ices wi h a,b) F8BT and c,d) MEH-PPV emissi e laye s a ϑ¼0∘unde op ical and elec ical ope a ion. Di e ences be ween PL and EL spec a may a ise due o confinemen o he emission zone ( ype A de ices) o esidual ansmission o he OLED exci a ion ligh ( ype B de ices). The TM0mode seen in he Type B F8BT de ice is no loca ed be ween he TE0and TE1mode due o he ma e ial’s aniso opy. 450 500 550 600 650 -30 -15 0 15 30 450 500 550 600 650 -30 -15 0 15 30 0 0.2 0.4 0.6 0.8 1 Figu e 7. Angle- esol ed EL spec um o a ype A OLED ab ica ed by he - mal e apo a ion comp ising a nanopa e ned ITO elec ode. Resonan ou coupling e ec s a e s ongly isible, indica ing ha he quali y o he e ched ITO pho onic c ys al s uc u e is su ficien o highly di ec ional ligh ou coupling. www.ad ancedsciencenews.com www.adp -jou nal.com Ad . Pho onics Res. 2023,4, 2200143 2200143 (7 o 9) © 2022 The Au ho s. Ad anced Pho onics Resea ch published by Wiley-VCH GmbH 26999293, 2023, 2, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/adp .202200143 by Uni e si a sbiblio hek Kiel, Wiley Online Lib a y on [20/08/2023]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License na ow-band abso p ion o analy e compounds o wa eleng h- dependen pho ode ec o sensi i i y. In ei he case, only a limi ed wa eleng h ange o he emission spec um is e ec i ely u ilized. Assuming spec al es ic ions o he o e all sensing sys em, highly di ec ional ligh emission in o na ow cone angles can be ob ained. Pola plo s o he emission in ensi y a specific wa eleng hs highligh ing his e ec a e shown in Figu e 9. 5. Conclusions In his wo k, we compa e wo di e en app oaches o ob ain di ec ional emission om OLED de ices employing pho onic c ys al slabs. In ype A de ices, he pe iodic nanopa e n is di ec ly in eg a ed in o he OLED s ack by pa e ning he ITO bo om elec ode be o e de ice ab ica ion. In ype B, de ices a con en ional OLED is combined wi h a nanopa e ned colo con e sion laye deposi ed on he subs a e backside. Despi e using he same fluo escen polyme s (F8BT and MEH-PPV) as he emissi e laye in bo h app oaches, di e ences in esonan ou coupling in ensi y a ise due o he di e en wa eguide p op- e ies. Op ical abso p ion in he addi ional OLED laye s limi s he esonance quali y ac o o he pho onic c ys al slab in ype A de ices. Addi ionally, he e ac i e index con as be ween he nanopa e ned elec ode and he high-index polyme laye s is low, esul ing in negligible di ec ional ligh ou coupling. In ype B de ices, on he o he hand, sha p ou coupling peaks a e obse - able a specific wa eleng hs and iewing angles. In eg a ed emis- sion spec a show o wa d di ec ionali y, whe eas di ec ional emission in o highe iewing angles is ob ainable by spec al fil e ing. Acknowledgemen s This p ojec has ecei ed unding om he Eu opean Resea ch Council (ERC) unde he Eu opean Union’s Ho izon 2020 esea ch and inno a ion p og amme (G an ag eemen no. 899861). Open Access unding enabled and o ganized by P ojek DEAL. Conflic o In e es The au ho s decla e no conflic o in e es . Au ho Con ibu ions J.B.: Expe imen concep ualiza ion and design, sample ab ica ion and cha ac e iza ion, isualiza ion, o iginal d a p epa a ion, e iew, and edi - ing; H.L.: Simula ion design and implemen a ion, ellipsome y da a fi ing, manusc ip p epa a ion (simula ion sec ion), e iew, and edi ing; G.B.: Sample ab ica ion and cha ac e iza ion (Figu e 7 OLED); T.N.: Pa ame e s udies; A.P.: AFM measu emen s; M.G.: Concep , unding acquisi ion, p ojec adminis a ion and supe ision, e iew, and edi ing. Da a A ailabili y S a emen The da a ha suppo he findings o his s udy a e a ailable om he co esponding au ho upon easonable eques . 0 0.5 1 0° 30° 60° 90°-90° -60° -30° (a) F8BT In ensi y (no m.) Type A Type B Lambe ian 0 0.5 1 0° 30° 60° 90°-90° -60° -30° (b) MEH-PPV In ensi y (no m.) Figu e 8. In eg a ed pola plo s o he emission cha ac e is ics o OLEDs wi h a) F8BT and b) MEH-PPV emissi e laye s in pho oluminescence. Type B de ices ea u e di ec ional o wa d emission wi h a dis inc in ensi y dip a ϑ¼0∘which can be a ibu ed o he op ical bandgap o he pho onic c ys al slab. 0 0.5 1 0° 30° 60° 90°-90° -60° -30° (a) Type B F8BT In ensi y (no m.) 600 nm 650 nm 700 nm 0 0.5 1 0° 30° 60° 90°-90° -60° -30° (b) Type B MEH-PPV In ensi y (no m.) Figu e 9. Pola plo s o he EL emission cha ac e is ics o ype B OLED de ices wi h a) F8BT and b) MEH-PPV CCLs a specific wa eleng hs. Highly di ec ional emission in o ex emely na ow cone angles is ob ained o bo h fluo escen ma e ials. www.ad ancedsciencenews.com www.adp -jou nal.com Ad . Pho onics Res. 2023,4, 2200143 2200143 (8 o 9) © 2022 The Au ho s. 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