Organic Light Emitting Diode (OLED)

1. Theory

• Definition: An organic light-emitting diode (OLED) is a multilayer thin-film diode of small molecules or polymers in which injected holes and electrons form excitons that emit light.
• Layered structure: Separate hole-transport, emitting and electron-transport layers between an anode (often ITO) and a cathode.
• Hopping transport: Carriers hop between disordered molecular sites, with mobility rising with field (Poole-Frenkel-like) and temperature.
• Excitons: Electrons and holes bind into tightly bound excitons, formed as singlets and triplets in a 1:3 ratio.
• Emitter generations: Fluorescent emitters use only singlets (at most 25% internal efficiency); phosphorescent (heavy-metal) and TADF emitters harvest triplets to approach 100%.
• Host-guest doping: A few percent of emitter in a conductive host receives exciton energy by Förster (long-range) and Dexter (short-range) transfer.

2. Working Principle

• Injection: Holes and electrons cross injection barriers at the electrodes (thermionic or Fowler-Nordheim injection).
• Transport: Space-charge-limited currents flow through the low-mobility layers.
• Recombination: Electrons and holes meet in the emitting layer by Langevin recombination and form excitons.
• Emission: Excitons decay radiatively from singlets (fluorescence), triplets (phosphorescence) or via reverse intersystem crossing (TADF).
• Efficiency chain: ${\eta }_{EQE}=\gamma {\eta }_{ST}{\Phi }_{PL}{\eta }_{out}$, the product of charge balance, spin factor, photoluminescence yield and outcoupling.
• Outcoupling limit: High-index organic layers trap light in waveguide, substrate and plasmon modes, so only about 20% leaves a planar device.
• Roll-off: At high brightness, exciton-exciton and exciton-polaron annihilation reduce efficiency.

3. Applications

• Smartphone, watch and tablet displays: Self-emissive pixels with true black, high contrast and thin, flexible or foldable panels.
• Televisions and monitors: Large OLED panels for premium high-contrast displays.
• Automotive and specialty lighting: Thin, uniform area lighting for rear lamps and design luminaires.

Name	Formula	Related Formulae	Variables/Constants
Hopping mobility: temperature and field dependence	$\mu \left(F,T\right)={\mu }_{\infty }\exp \left[-{\left(\frac{2\sigma }{3k_{B}T}\right)}^2\right]\exp \left(\gamma \sqrt{F}\right)$	${\nu }_{ij}={\nu }_0\exp \left(-2{\gamma }_w{r}_{ij}\right)\exp \left(-\frac{{\epsilon }_j-{\epsilon }_i}{k_{B}T}\right)\left({\epsilon }_j>{\epsilon }_i\right)$ ${\nu }_{ij}={\nu }_0\exp \left(-2{\gamma }_w{r}_{ij}\right)\left({\epsilon }_j\le {\epsilon }_i\right)$	$\begin{array}{r}\mu \left(F,T\right):driftmobilityatthefieldFand\\ temperatureTinadisorderedorganicfilm\\ (theGaussiandisorderformofthe\\ temperaturedependencewiththe\\ Poole-Frenkelformofthefield\\ dependence)\end{array}$ $\begin{array}{r}{\mu }_{\infty }:mobilityextrapolatedtoinfinite\\ temperature\end{array}$ $\begin{array}{r}\sigma :width(standarddeviation)ofthe\\ Gaussiandensityofhoppingstates,ofthe\\ orderof0.1eV\end{array}$ $\begin{array}{r}\gamma :Poole-Frenkelcoefficient,afitting\\ parameterthatdependsonthetemperature\\ andonthedisorder(intheGaussiandisorder\\ modelofH.Bassler,phys.stat.sol.(b)175,\\ 15(1993),\\ \gamma =C\left[{\left(\sigma /k_{B}T\right)}^2-{\Sigma }^2\right]\\ with\\ C\approx 2.9\times 10^{-4}(cm/V{)}^{1/2}and\Sigma the\\ positionaldisorder,for\Sigma \ge 1.5;themodelfits\\ the\sqrt{F}lawonlyoveralimitedrangeoffield)\end{array}$ $F:electricfield$ $\begin{array}{r}{\nu }_{ij}:Miller-Abrahamshoppingratefromthe\\ siteitothesitej\end{array}$ ${\nu }_0:attemptfrequency$ $\begin{array}{r}{\gamma }_w:inverselocalizationlengthofthe\\ wavefunction\end{array}$ $r_{ij}:distancebetweenthesites$ $\begin{array}{r}{\epsilon }_i,{\epsilon }_j:energiesofthetwosites(ahop\\ upinenergyispenalizedbytheBoltzmann\\ factorandahopdownisnot)\end{array}$ $k_B:Boltzmannconstant$
Space-charge-limited current	$J=\frac{9}{8}\epsilon \mu \frac{V^2}{d^3}$	$J=\frac{9}{8}\epsilon {\mu }_0\frac{V^2}{d^3}\exp \left(0.89\gamma \sqrt{\frac{V}{d}}\right)$	$\begin{array}{r}J:currentdensityofthesingle-carrier\\ devicewithanohmicinjectingcontactand\\ notraps(theMott-Gurneylaw)\end{array}$ $\epsilon :permittivityoftheorganiclayer$ $\mu :mobility,assumedconstant$ $\begin{array}{r}V:appliedvoltage(correctedforthe\\ built-involtageandtheseries\\ resistance)\end{array}$ $d:layerthickness$ $\begin{array}{r}{\mu }_0,\gamma :zero-fieldmobilityand\\ Poole-Frenkelcoefficientofamobility\\ {\mu }_0\exp (\gamma \sqrt{F}),usedinthesecondexpression\\ (theMurgatroydform,withtheaverage\\ fieldV/dintheexponent)\end{array}$ $\begin{array}{r}(anOLEDisadouble-carrierdevicewith\\ recombination,sothesingle-carrierlaw\\ appliestothehole-onlyandthe\\ electron-onlytestdevicesusedtoextract\\ themobilities)\end{array}$
Langevin recombination of electrons and holes	$R_L=\frac{q\left({\mu }_n+{\mu }_p\right)}{\epsilon }np$	$k_L=\frac{q\left({\mu }_n+{\mu }_p\right)}{\epsilon }$ ${\gamma }_L\approx \frac{J_{rec}}{J}$	$\begin{array}{r}{R}_L:recombinationrateperunitvolumeof\\ theelectronsandholesthatmeetbydrift\\ intheirmutualCoulombfield(the\\ Langevinprocess,validwhenthemeanfree\\ pathisshorterthanthecaptureradius,\\ asinthelow-mobilityorganicfilms)\end{array}$ $q:elementarycharge$ ${\mu }_n,{\mu }_p:mobilitiesofelectronsandholes$ $\epsilon :permittivityoftheorganiclayer$ $n,p:densitiesofelectronsandholes$ $k_L:Langevinrecombinationcoefficient$ $\begin{array}{r}{\gamma }_L:fractionoftheinjectedcurrentthat\\ recombinesinthedevice(adefinitionof\\ thechargebalancefactorintermsofthe\\ recombinationcurrent{J}_{rec}),whichisclose\\ tooneinawell-balanceddevicewith\\ blockinglayersandlowerwhenonecarrier\\ typereachestheoppositeelectrode\\ withoutrecombining\end{array}$ $\begin{array}{r}(themeasuredrecombinationcoefficientin\\ somematerialsislowerthantheLangevin\\ value,andthereductionfactoristreated\\ asaparameter)\end{array}$
Charge injection from the electrode	$J_{FN}=\frac{q^3{F}^2}{8\pi h{\Phi }_B}\exp \left(-\frac{8\pi \sqrt{2m^{\ast }}{\Phi }_B^{3/2}}{3hqF}\right)$	$J_{RS}=A^{\ast }{T}^2\exp \left(-\frac{{\Phi }_B-\sqrt{q^{3}F/\left(4\pi \epsilon \right)}}{k_{B}T}\right)$	$\begin{array}{r}{J}_{FN}:Fowler-Nordheimtunnellingcurrent\\ densitythroughatriangularbarrier\end{array}$ $q:elementarycharge$ $F:electricfieldattheinterface$ $h:Planckconstant$ $\begin{array}{r}{\Phi }_B:injectionbarrierheight,asan\\ energy,betweentheFermilevelofthe\\ electrodeandthetransportlevelofthe\\ organiclayer\end{array}$ $m^{\ast }:effectivemassofthetunnellingcarrier$ $\begin{array}{r}{J}_{RS}:Richardson-Schottkythermionic\\ emissionovertheimage-force-lowered\\ barrier\end{array}$ $A^{\ast }:Richardsonconstant$ $T:temperature$ $\epsilon :permittivityoftheorganiclayer$ $k_B:Boltzmannconstant$ $\begin{array}{r}(theinjectionintoadisorderedorganic\\ layerisbetterdescribedbyathermally\\ assistedhoppingmodel;thetwo\\ expressionsarethestandardlimitsfora\\ crystallinesemiconductor)\end{array}$
External quantum efficiency and spin statistics	${\eta }_{EQE}=\gamma {\eta }_{ST}{\Phi }_{PL}{\eta }_{out}$	${\eta }_{IQE}=\gamma {\eta }_{ST}{\Phi }_{PL}$ ${\eta }_{ST}=0.25\left(fluorescence\right),{\eta }_{ST}\approx 1\left(phosphorescence,TADF\right)$	$\begin{array}{r}{\eta }_{EQE}:externalquantumefficiency,photons\\ outperelectroninjected\end{array}$ $\begin{array}{r}\gamma :chargebalancefactor,thefractionof\\ theinjectedelectronsthatforman\\ exciton(equaltoonewheneveryelectron\\ findsaholeintheemittinglayer)\end{array}$ $\begin{array}{r}{\eta }_{ST}:fractionoftheexcitonsthatcanemit\\ light(thesingletsareonequarterofthe\\ excitonsformedbytheelectrical\\ injectionandthetripletsarethree\\ quarters)\end{array}$ $\begin{array}{r}{\Phi }_{PL}:photoluminescencequantumyieldofthe\\ emitterinthefilm\end{array}$ ${\eta }_{out}:outcouplingefficiency$ ${\eta }_{IQE}:internalquantumefficiency$ $\begin{array}{r}(theexpressionforafluorescentemitter\\ with{\eta }_{ST}=0.25includesthecaseinwhich\\ triplet-tripletannihilationrecyclessome\\ tripletsintosinglets,whichraisesthe\\ valueabove0.25)\end{array}$
Energy transfer between host and guest molecules	$k_F=\frac{1}{{\tau }_D}{\left(\frac{R_0}{R}\right)}^6$	$R_0^6=\frac{9\ln 10{\kappa }^2{\Phi }_D}{128{\pi }^5{N}_A{n}^4}J$ $k_{Dexter}=K{J}^{\prime }\exp \left(-\frac{2R}{L}\right)$	$\begin{array}{r}{k}_F:rateoftheFoerstertransferofan\\ excitonfromadonortoanacceptor\\ molecule(adipole-dipoleinteraction)\end{array}$ $\begin{array}{r}{\tau }_D:lifetimeoftheexciteddonorwithout\\ theacceptor\end{array}$ $R:distancebetweenthedonorandtheacceptor$ $\begin{array}{r}{R}_0:Foersterradius,thedistanceatwhich\\ thetransferrateequalsthedecayrateof\\ thedonor\end{array}$ $\begin{array}{r}{\kappa }^2:orientationfactorofthetwo\\ transitiondipoles,equalto2/3for\\ randomorientations\end{array}$ ${\Phi }_D:photoluminescenceyieldofthedonor$ $N_A:Avogadroconstant$ $n:refractiveindexofthemedium$ $\begin{array}{r}J:overlapintegralofthedonoremission\\ andtheacceptorabsorptionweightedwith\\ {\lambda }^4(theexpressionisinconsistentSIunits,\\ withthemolarextinctioncoefficientin\\ m^{2}mo{l}^{-1}andthewavelengthinm;withthe\\ coefficientin{M}^{-1}c{m}^{-1}andthewavelengthin\\ cmthenumeratorbecomes9000\ln 10,andforJ\\ in{M}^{-1}c{m}^{-1}n{m}^{4}theresultis\\ R_0=0.211{\left({\kappa }^2{n}^{-4}{\Phi }_{D}J\right)}^{1/6}\\ inangstrom(Lakowicz);bothgive49.8angstrom\\ fortheexampleinthequestions)\end{array}$ $\begin{array}{r}{k}_{Dexter}:rateoftheDexter(exchange)\\ transfer,whichneedstheoverlapofthe\\ orbitalsandcanmovetriplets\end{array}$ $\begin{array}{r}K,J^{\prime },L:constantwiththedimensionof\\ anenergysquared,thespectraloverlap\\ normalizedtotheextinctioncoefficient,\\ andthesumofthevanderWaalsradiiof\\ thedonorandtheacceptor(thedecaywith\\ thedistanceisexponential,soitsrange\\ isabout1nmcomparedwithseveralnmfor\\ theFoerstertransfer)\end{array}$
Thermally activated delayed fluorescence	$k_{RISC}={\Phi }_{SOC}\exp \left(-\frac{\Delta E_{ST}}{k_{B}T}\right)$	$\Delta E_{ST}=E_{S_1}-E_{T_1}=2K_{ex}$ ${\tau }_{delayed}\approx \frac{1}{k_{RISC}\left(1-{\Phi }_{ISC}\right)+k_T}$	$\begin{array}{r}{k}_{RISC}:rateofreverseintersystemcrossing\\ fromthelowesttriplettothelowest\\ singletstate\end{array}$ $\begin{array}{r}{\Phi }_{SOC}:prefactorthatisrelatedtothe\\ spin-orbitcouplingbetweenthetwostates\end{array}$ $\Delta E_{ST}:singlet-tripletenergygap$ $k_B,T:Boltzmannconstantandtemperature$ $\begin{array}{r}{E}_{S_1},E_{T_1}:energiesofthelowestsinglet\\ andtripletexcitedstates\end{array}$ $\begin{array}{r}{K}_{ex}:exchangeintegralbetweenthehighest\\ occupiedandthelowestunoccupied\\ orbitals(itissmallwhenthetwo\\ orbitalsarespatiallyseparatedonthe\\ donorandtheacceptorpartsofthe\\ molecule)\end{array}$ $\begin{array}{r}{\tau }_{delayed}:lifetimeofthedelayed\\ fluorescencewhenthesingletdecaysmuch\\ fasterthanthetriplet(eachRISCevent\\ returnstothetripletwiththeprobability\\ {\Phi }_{ISC},soonlythefraction1-{\Phi }_{ISC}removes\\ thetriplet);1/k_{RISC}isonlythelimitofa\\ small{\Phi }_{ISC}andnotripletloss\end{array}$ ${\Phi }_{ISC}:intersystemcrossingyieldofthesinglet$ $\begin{array}{r}{k}_T:non-radiative(andphosphorescent)\\ decayrateofthetriplet\end{array}$
Efficiency roll-off by exciton-exciton annihilation	$\frac{{\eta }_{EQE}\left(J\right)}{{\eta }_0}=\frac{J_0}{4J}\left[\sqrt{1+\frac{8J}{J_0}}-1\right]$	$J_0=\frac{4qd}{k_{TT}{\tau }^2}$ $\frac{dn}{dt}=\frac{J}{qd}-\frac{n}{\tau }-\frac{1}{2}{k}_{TT}{n}^2$ $\frac{{\eta }_{EQE}\left(J\right)}{{\eta }_0}\approx \frac{1}{1+{\left(J/J_e\right)}^{1/\left(m+1\right)}}$	$\begin{array}{r}{\eta }_{EQE}\left(J\right):externalquantumefficiencyatthe\\ currentdensityJ\end{array}$ $\begin{array}{r}{\eta }_0:efficiencywithoutannihilation(the\\ low-currentvalue)\end{array}$ $\begin{array}{r}{J}_0:currentdensityatwhichthe\\ efficiencyisonehalfof{\eta }_0\end{array}$ $q:elementarycharge$ $\begin{array}{r}d:thicknessofthezoneinwhichthe\\ excitonsarepresent\end{array}$ $\begin{array}{r}{k}_{TT}:rateconstantoftriplet-triplet\\ annihilation,intheconventionofthe\\ rateequationwiththefactor1/2\end{array}$ $\tau :tripletlifetime$ $n:tripletexcitondensity$ $\begin{array}{r}{J}_e,m:fittingparametersoftheempirical\\ exciton-polaronform(thequenchingofthe\\ excitonsbythecharges),whichfitssome\\ measuredroll-offcurvesbetterthanthe\\ exciton-excitonform\end{array}$
Optical outcoupling	${\eta }_{out}\approx \frac{1}{2n_{org}^2}$	${\eta }_{out}={\eta }_{air}=1-{\eta }_{sub}-{\eta }_{wg}-{\eta }_{spp}$ ${\theta }_c=\arcsin \left(\frac{n_{air}}{n_{org}}\right)$	$\begin{array}{r}{\eta }_{out}:fractionofthegeneratedphotons\\ thatleaveintotheair,fora\\ bottom-emittingdeviceonaglass\\ substrate(theclassicalray-optics\\ estimate)\end{array}$ $\begin{array}{r}{n}_{org}:refractiveindexoftheorganic\\ layers,about1.7to1.8\end{array}$ ${\eta }_{air}:fractionintheairmodes$ $\begin{array}{r}{\eta }_{sub}:fractiontrappedinthesubstrate\\ modes,whichreachtheglassbutare\\ reflectedattheglass-airinterface\end{array}$ $\begin{array}{r}{\eta }_{wg}:fractionguidedintheorganiclayers\\ andthetransparentelectrode(the\\ waveguidemodes)\end{array}$ $\begin{array}{r}{\eta }_{spp}:fractionlosttothesurfaceplasmon\\ polaritonsofthemetalcathode,whichis\\ largefortheemitterclosetothemetal\end{array}$ $\begin{array}{r}{\theta }_c:criticalangleattheorganic-air\\ interface(theraymodelignoresthe\\ interferenceinthethinlayersandthe\\ near-fieldcouplingofthedipole,sothe\\ exactfractionsarecalculatedwitha\\ dipolemodelofthelayerstack)\end{array}$
Luminance, current efficiency and power efficacy	${\Phi }_v=\pi LA$	${\eta }_C=\frac{L}{J}=\frac{{\Phi }_v}{\pi I}$ ${\eta }_P=\frac{{\Phi }_v}{IV}=\frac{\pi {\eta }_C}{V}$	$\begin{array}{r}{\Phi }_v:luminousfluxemittedbyaLambertian\\ surface\end{array}$ $L:luminance(cd/m^2)$ $A:emittingarea$ ${\eta }_C:currentefficiency(cd/A)$ $J,I:currentdensityandcurrent$ ${\eta }_P:powerefficacy(lm/W)$ $\begin{array}{r}V:operatingvoltage(theluminousfluxof\\ arealspectrumistheintegralof683\\ lm/Wtimestheeyesensitivityfunction\\ timesthespectralpower,asontheLight\\ EmittingDiodepage,andtheLambertian\\ patternisanassumption)\end{array}$

Important Questions

Ques: How does an OLED work, and what limits its efficiency?

A thin film of organic molecules or polymer is placed between an anode and a cathode. Holes and electrons are injected (the injection row), move by hopping through the transport layers (the mobility row), and meet in the emitting layer where they form excitons, which emit a photon. The efficiency is the product of four factors (the efficiency row): the charge balance, the fraction of excitons that can emit (one quarter singlets in a fluorescent emitter), the quantum yield of the emitter and the outcoupling. The first OLED with a double organic layer of low operating voltage was reported by Tang and VanSlyke, and the layered structure with separate transport and emitting layers is still the basis of the devices. Reference: C.W. Tang and S.A. VanSlyke, “Organic electroluminescent diodes,” Appl. Phys. Lett. 51, 913 (1987).

Ques: Why do phosphorescent and TADF emitters raise the efficiency?

The recombination of the injected charges forms singlet and triplet excitons in the ratio 1:3, so a fluorescent emitter can use only one quarter of the excitons and its internal quantum efficiency is limited to 25% (without triplet recycling). A phosphorescent emitter, which contains a heavy metal such as iridium, has a strong spin-orbit coupling that makes the triplet radiative, and the internal efficiency can approach 100%. A TADF emitter has a small singlet-triplet gap, so the triplets return to the singlet state by thermal activation with $k_{RISC}={\Phi }_{SOC}\exp (-\Delta E_{ST}/k_{B}T)$. As an illustration, the Boltzmann factor is 0.145 for a gap of 0.05 eV, 0.021 for 0.1 eV and $4.4\times 10^{-4}$ for 0.2 eV at 300 K, which is why the gap has to be made of the order of 0.1 eV or less, and the prefactor that contains the spin-orbit coupling is also important. Reference: M.A. Baldo et al., “Highly efficient phosphorescent emission from organic electroluminescent devices,” Nature 395, 151 (1998); H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi, “Highly efficient organic light-emitting diodes from delayed fluorescence,” Nature 492, 234 (2012).

Ques: Why does the efficiency of an OLED fall at a high brightness (roll-off)?

At a high current the density of triplet excitons is high, and two excitons can annihilate, which removes one of them. The rate equation with the annihilation term gives an efficiency of $\eta /{\eta }_0=(J_0/4J)[\sqrt{1+8J/J_0}-1]$ with $J_0=4qd/(k_{TT}{\tau }^2)$. With the assumed values $d=20$ nm, $\tau =1\mu$s and $k_{TT}=10^{-12}$ cm${}^3$/s, $J_0=1.3$ A/cm${}^2$, and the efficiency is 0.98 of ${\eta }_0$ at 10 mA/cm${}^2$, 0.88 at 100 mA/cm${}^2$ and 0.50 at $J_0$ (the numbers are computed from the formula and are illustrative). Other mechanisms (the quenching of the excitons by charges, the field-induced dissociation and the loss of charge balance) also contribute, and an analysis of measured curves in a study of the roll-off under a magnetic field found that the exciton-polaron form fitted the data better than the exciton-exciton form. Reference: M.A. Baldo, C. Adachi and S.R. Forrest, “Transient analysis of organic electrophosphorescence. II. Transient analysis of triplet-triplet annihilation,” Phys. Rev. B 62, 10967 (2000) (recalled; the closed form was confirmed in the form used by arXiv:1910.02583, “Reducing the efficiency roll-off in organic light-emitting diodes at high currents under external magnetic fields”).

Ques: Why does only about 20% of the light leave a planar OLED?

The organic layers have a refractive index of 1.7 to 1.8, higher than the glass and the air, so most of the light is trapped by total internal reflection in the substrate and in the waveguide formed by the organic layers and the transparent anode, and a part of it is lost to the surface plasmon polaritons of the metal cathode. The classical estimate $1/(2n^2)$ is 17% for $n=1.7$ and 15% for $n=1.8$. A presentation of S. Forrest at a US Department of Energy meeting states that 80% of the light is trapped in a baseline device (an outcoupling and an EQE of about 20% for an internal efficiency near 100%), and shows microlens arrays and low-index grids that raise the outcoupling to about 40% and 60% (the split of the trapped light among the substrate, the waveguide and the plasmon modes in that slide is not labelled, and the reading of 20%, 20%, 15% and 45% for air, substrate, waveguide and plasmon modes is an inference). Reference: S.R. Forrest, “OLED outcoupling,” presentation at the US Department of Energy solid-state lighting workshop, Long Beach (2017), energy.gov/sites/prod/files/2017/02/f34/forrest_oled-outcoupling_longbeach2017.pdf. The $1/(2n^2)$ ray-optics estimate is from N.C. Greenham et al. (with R.H. Friend and D.D.C. Bradley), “Angular dependence of the emission from a conjugated polymer light-emitting diode: implications for efficiency calculations,” Adv. Mater. 6, 491 (1994), DOI 10.1002/adma.19940060612.

Ques: How are the excitons moved from the host to the guest molecule in a doped emitting layer?

Most OLEDs dilute a few percent of an emitter (the guest) in a host that conducts the charges. The host excitons transfer their energy to the guest either by the long-range Foerster transfer, whose rate is $(1/{\tau }_D)(R_0/R{)}^6$ and which moves singlets over several nanometres, or by the short-range Dexter transfer (the exchange interaction, with a range of about 1 nm), which also moves triplets. The Foerster radius follows from the overlap of the donor emission and the acceptor absorption. For an overlap integral of $10^{15}$ M${}^{-1}$cm${}^{-1}$nm${}^4$, ${\kappa }^2=2/3$, $n=1.4$ and ${\Phi }_D=1$, the radius is 50 angstrom (computed from the two expressions given in the table, which agree). The numbers are illustrative; in OLED films $n$ is about 1.7 and the overlap integral is specific to the pair of molecules. Reference: T. Foerster, “Zwischenmolekulare Energiewanderung und Fluoreszenz,” Ann. Phys. 437, 55 (1948) (recalled).

Related pages in this vault: Quantum Dot LED (QLED), Perovskite LED (PeLED), Micro-LED, Light Emitting Diode (Homojunction and Heterojunction LED), Ultraviolet LED (AlGaN Deep-UV LED), Thin-Film Transistors (a-Si, LTPS, IGZO, Organic), Organic Photodetector (OPD), Organic Solar Cell (Bulk Heterojunction), Light Emitting Diodes (InGaN, AlInGaP, UV and White).