Thèses sur le sujet « Inorganic light-emitting diodes »

The aim of this thesis work was to fabricate a hybrid LED using organic-inorganic ZnO materials. The goal of the project was to get an efficient white light emission from zinc oxide (ZnO) nanorods active layer. Since most of the organic materials are good for hole mobility and most of the inorganic materials are good for electron mobility, it is possible to fabricate a high performance heterostructure electroluminescence device from organic-inorganic materials. This thesis work was an attempt towards fabricating such a high electroluminescence LED from hybrid materials in which polymer acts as a p-type material and ZnO acts as a n-type material. The growth mechanism of ZnO nanorods using low-temperature aqueous solution method has been studied and nanorods (NRs) growth was examined with scanning electron microscope (SEM). Optimum hole injection polymers have been studied. Finally, the fabricated device was characterized using parameter analyzer. The fabricated device worked as a diode i.e. it rectified current as expected and the desirable light emission has almost been achieved.

Zinc oxide, with its direct wide bandgap and high exciton binding energy, is a promising material for optoelectronic devices. Quantum confinement effect and high surface to volume ratio of the nanowires imparts unique properties to them and makes them appealing for researchers. So far, zinc oxide nanowires have been used to fabricate various optoelectronic devices such as light emitting diodes, solar cells, sensors and photodetectors. To fabricate those optoelectronic devices, many different synthesis methods such as metal organic chemical vapor deposition, chemical vapor deposition, pulsed laser deposition, electrodeposition and hydrothermal method have been explored. Among them, hydrothermal method is the most feasible one in terms of simplicity and low cost. In this thesis, hydrothermal method was chosen to synthesize zinc oxide nanowires. Synthesized zinc oxide nanowires were then used as electrically active components in light emitting diodes and ultraviolet photodetectors. Hybrid light emitting diodes, composed of inorganic/organic hybrids are appealing due to their flexibility, lightweight nature and low cost production methods. Beside the zinc oxide nanowires, complementary poly [2- methoxy -5- (2- ethylhexyloxy) - 1,4 -phenylenevinylene] MEH-PPV and poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) hole conducting polymers were used to fabricate hybrid light emitting diodes in this work. Optoelectronic properties of the fabricated light emitting diodes were investigated. Zinc oxide emits light within a wide range in the visible region due to its near band edge and deep level emissions. Utilizing this property, violet-white light emitting diodes were fabricated and characterized. Moreover, to take advantage over the responsivity of zinc oxide to ultraviolet light, ultraviolet photodetectors utilizing hydrothermally grown zinc oxide nanowires were fabricated. Single walled carbon nanotube (SWNT) thin films were used as transparent electrodes for the photodetectors. Optoelectronic properties of the transparent and flexible devices were investigated. A high on-off current ratio around 260000 and low decay time about 16 seconds were obtained. Results obtained in this thesis reveal the great potential of the use of solution grown zinc oxide nanowires in various optoelectronic devices that are flexible and transparent.

Mestrado em Engenharia Física
Nos anos recentes a iluminação de estado sólido impulsionou alternativas de iluminação efí cientes e ecológicas. Os desafi os correntes envolvem o desenvolvimento de materiais emissores de luz que convertem radiação de uma determinada energia para radiação de energia mais baixa, na gama do visível. Esta tese estuda um complexo novo, Tb(NaI)3(H2O)2 onde NaI é o ácido nalidíxico, que emite na região do verde e é estável sob iluminação no ultravioleta. Este foi incorporado em materiais híbridos orgânico-inorgânico tripodais com dois pesos moleculares médios (3000 e 5000 g.mol-1, denominados t- U(3000) e t-U(5000) respetivamente) que permitem o processamento de monólitos e fi lmes com forma e espessura controlada. Estes híbridos também aumentam o rendimento quântico absoluto de emissão de 0.11 medidos para o Tb(NaI)3(H2O)2 isolado para ~0.82 após incorporação no t-U(5000). Foi também demonstrado o potencial de usar estes materiais híbridos como emissores na região verde para uso em iluminação de estado sólido através do revestimento do díodo emissor na região ultravioleta (365 nm). Este LED apresenta uma efi cácia de 1.3 lm.W􀀀1.
In the last few years, solid state light-emitting diodes (LEDs) have been driving the lighting industry towards energy e cient and environmental friendly lighting. Current challenges encompass e cient and low-cost downconverting photoluminescent phosphors with emission in the visible region. This thesis will cover a novel UV-photostable green emitting complex, Tb(NaI)3(H2O)2 where NaI is nalidixic acid, was incorporated into organic-inorganic tripodal hybrid materials with two average molecular weights (3000 and 5000 g.mol{1, termed as t- U(5000) and t-U(3000), respectively) which enable the easy shaping of monoliths and lms with controlled thickness. Moreover, the hybrid hosts boost the Tb3+ green absolute emission quantum yield from 0.11 measured for the isolated Tb(NaI)3(H2O)2 complex to 0.82 after incorporation into t-U(5000). The potential use of the hybrid materials as UV-down converting green-emitting phosphors for solid state lighting was demonstrated by means of coating a near-UV LED (365 nm). This LED shows an e cacy of 1.3 lm.W􀀀1.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.
Includes bibliographical references.
Difficulties with traditional methods of synthesis and film formation for conducting polymers, many of which are insoluble, motivate the development of CVD methods. Indeed, conjugated polymers with rigid linear backbones typically crystallize readily and overcoming the resultant heat of crystallization makes them difficult to dissolve. Poly(3,4-ethylenedioxythiophene) (PEDOT) thin films were obtained through oxidative chemical vapor deposition (oCVD) by using a new oxidant- bromine. The use of bromine eliminates any post processing rinsing step required with other oxidants like iron chloride and hence makes the process completely dry. Accelerated aging experiments show longer retention of electrical conductivity for the PEDOT films obtained using bromine as the oxidant. Conductivities as high as 380 S/cm were obtained for PEDOT films deposited using bromine as the oxidant at 80 'C, which is significantly higher than that for PEDOT films deposited using iron chloride as the oxidant at the same temperature. Cross-sectional SEM of the PEDOT films deposited using bromine on silicon trench wafers demonstrates high conformal deposition of the films. All the results show the possibility of depositing highly conducting, conformal PEDOT films on any substrate including silicon, glass, paper, plastic. One of the many applications of conducting polymer is as hole-transport layer in light emitting diode. To be competitive in the LED market, improvements in hybrid-LED quantum efficiencies as well as demonstrations of long-lived HLED structures are necessary. In this work, we consider improvement in the stability of the HLED. The device fabricated can be configured as ITO/ Poly (EDOT-co-TAA)/CdSe (ZnS)/ Au. All the materials used in the device synthesis are stable in ambient conditions and all the synthesis steps on ITO substrate are done either in air or in very moderate pressure conditions. This significantly reduces the cost of the device fabrication by obviating the need of packaging layers and ultrahigh vacuum tools. The operating voltage as low as 4.3 V have been obtained for red-LEDs. We believe that with optimization of various layers in the device, further improvements can be made. For green LEDs we obtained the characteristic IV curve of a diode, but we still need to work on getting a functioning green LED.
by Hitesh Chelawat.
S.M.

Thin film transistors (TFTs) can be used to determine the bulk-like mobilities of amorphous semiconductors. Different organic hole transporters (HTs) are under investigation including spiro-TPD, 2TNATA, NPB and TPD which are commonly used in organic light-emitting diodes (OLEDs). In addition, we also measure the TFT hole mobilities of two iridium phosphors: Ir(ppy)3 and Ir(piq)3. These materials were grown on two different gate dielectric surfaces which were SiO2 and polystyrene (PS). On SiO2, the TFT mobilities are found to be 1-2 orders smaller than the bulk hole mobilities as evaluated independently by time-of-flight (TOF) technique. On the other hand, on PS gate dielectric layer, the TFT mobilities of these hole transporters are found to be in good agreement with TOF data. A thickness dependence measurement was carried out on TFT with PS. We found that only 10nm of organic semiconductor is sufficient for TFTs to achieve TOF mobilities. We further investigate why organic semiconductors on SiO2 have such huge reduction of mobilities. Temperature dependent mobility measurements were carried out and the data were analyzed by the Gaussian Disorder Model (GDM). We found that on SiO2 surface, when compared to the bulk values, the energetic disorders (σ) of the HTs increase and simultaneously, the high temperature limits (∞) of the carrier mobilities decrease. Both σ and ∞ contribute to the reduction of the carrier mobility. The increase in σ is related to the presence of randomly oriented polar Si-O bonds. The reduction of ∞ is topological in origin and is related to the orientations of the more planar molecules on SiO2. The more planar molecules tend to lie horizontally on the surface and such orientation is unfavorable for charge transport in TFT configuration. Hybrid organic/inorganic perovskites have emerged as an outstanding material for photovoltaic cells. In the second part of this work, we setup a repeatable perovskite recipe and optimized the system under different conditions. Under certain circumstances, a perovskite solar cell with power conversion efficiency ~9% can be achieved with PEDOT:PSS as hole transporting layer with the conventional structure.

This thesis consists of three main studies: magnetic field effects in thermally activated delayed fluorescent (TADF) organic light emitting diodes (OLEDs), magnetic field effects in bipolar and unipolar polythiophene (P3HT) devices and a study of hybrid organic/inorganic perovskite devices. Spin-dependent transport and recombination processes of spin-pair species have been detected by magnetic field effect (MFE) technique in carbon-based semi- conductor devices. Magneto-electroluminescence (MEL) and magneto-conductivity have been measured as a function of the applied magnetic field, B, in light emitting diodes. TADF materials have been used instead of simple fluorescent materials in OLEDs. We have observed very large magnetic response with TADF materials. The second study is magnetic field effects of regio-regular P3HT based OLED devices. P3HT is a well known semiconducting polymer, and its electrical properties such as magneto-conductance can be affected by an applied magnetic field. P3HT was chosen because it exhibits a sign change in magnetoresistance (MR) as the bias is increased. Unipolar and bipolar devices have been fabricated with different electrode materials to understand which model can be best to explain organic magnetoresistance effect, possibly depending on the operating regime of the device. Transport and luminescence spectroscopies were studied to isolate the different mechanisms and identify their fingerprints. The third study is on hybrid organic-inorganic perovskite devices. With the potential of achieving very high efficiencies and the very low production costs, perovskite solar cells have become commercially attractive. Scanning electron microscopy (SEM) images and absorption spectrum of the films were compared in single-step solution, two-step solution and solution-assisted vapor deposition techniques. Grain size, morphology and thickness parameters of perovskite films were studied within these techniques. Perovskite solar cells were fabricated and their efficiencies were measured.

Le rôle que joue l’azote sur les propriétés luminescentes de centres luminescents (effet néphélauxétique, champ cristallin) a déjà été largement démontré dans les matériaux (oxy)nitrures. Ce travail de thèse s’inscrit dans la recherche de nouveaux luminophores azotés, les carbodiimides inorganiques, pour une application diodes blanches. Ainsi, une méthode de synthèse polyvalente à partir de nitrure de carbone a été développée pour la synthèse de différents composés carbodiimides dopés par des ions terres rares ou de métaux de transition. Les propriétés structurales et optiques des composés SrCN2 :Eu2+ (λem = 620 nm ; rouge), CaCN2 :Mn2+ (λem = 680 nm ; rouge), CaCN2 : Ce3+ (λem = 462 nm ; bleue) et ZnCN2 :Mn2+ (λem = 585 nm ; orange) sont discutées. La modulation de l’émission du bleu au rouge est rendue possible par un co-dopage Ce3+/Mn2+ dans CaCN2. La luminescence intrinsèque bleue de ZnCN2 est également reportée
The role that nitrogen plays on the luminescent properties of luminescent centers (nephelauxetic effect, crystal field) has already been widely demonstrated in (oxy)nitride materials. This thesis work focuses on the search of new nitrogen-containing phosphors, i.e. inorganic carbodiimides, for WLED applications. Thus, a versatile synthesis method based on carbon nitride has been developed for the synthesis of various carbodiimide compounds doped with rare earth or transition metal ions. The structural and optical properties of SrCN2 :Eu2+ (λem = 620 nm ; red), CaCN2 :Mn2+ (λem = 680 nm ; red), CaCN2 :Ce3+ (λem = 462 nm ; blue) and ZnCN2 :Mn2+ (λem = 585 nm ; orange) compounds are discussed. The modulation of the emission from blue to red is made achiveable by Ce3+/Mn2+ co-doping in CaCN2. The intrinsic blue luminescence of ZnCN2 is also reported

The piezo-phototronics effect is the three way coupling of semiconductor properties, photonics and piezoelectricity in the same material. Research on piezo-phototronics effect has illustrated its application on various Zinc Oxide (ZnO) nanowire based devices, yet a systematical study with comprehensive theoretical model is still missing. Here we have designed experiments on wider variety of materials to investigate the mechanism of the piezo-phototronics effect, and then built up a theoretical model for more thorough understanding. Experimental results are shown for Cadmium Sulfide (CdS) photodetectors for visible light detection, inorganic/organic hybrid Light Emitting Diodes (LEDs) and LED arrays, and it is demonstrated that strain can significantly tune the performance of these optoelectronic devices. Theoretical methodologies are proposed for Metal-Semiconductor-Metal (MSM) structure and p-n junctions, including analytical solutions and Finite Element Method (FEM) simulations. For Schottky contacts in photodetectors, barrier height change is determined as the main reason for the effect, and an exponential relationship between applied external strain and the device current is discovered, and is qualitatively confirmed from experimental results. For p-n junctions in LEDs, change in size of depletion region under strain is credited for the current change, and a charge channel is predicted for large strain, which gives explanation for the observed gigantic enhancement of light emission efficiency in experiments.

Phases organiques luminescentes qui sont incorporés dans une matrice inorganique conductrice est proposé dans cette étude pour la couche active d'une diode émettant de la lumière hybride. Dans ce composite, le colorant organique joue le rôle de site de recombinaison radiative de porteurs de charge qui sont injectées dans la matrice de transport ambipolaire inorganique. Comme l'un des combinaisons de matériaux de candidat, bicouche et des films minces composites de ZnSe et un complexe d'iridium rouge (Ir(BPA)) émetteur de lumière organique ont été préparé in situ par UHV technique d'évaporation thermique. Les alignements de bande d'énergie mesurée par spectroscopie de photoélectrons (PES) pour le ZnSe/Ir(BPA)et deux couches de ZnSe+Ir(BPA) révèlent que le composite HOMO et LUMO du colorant organique sont positionnées dans la largeur de bande interdite de ZnSe. Cette gamme offre les forces motrices énergiques nécessaires pour les transferts d'électrons et de trous de ZnSe à Ir(BPA). Par l'interprétation des données du PES,la composition chimique des interfaces ont également été déterminés. Le ZnSe/Ir(BPA) interface est réactive, même si elle est d'une pureté de matériaux de haute.Pendant ce temps, l'Ir (BPA)/ZnSe interface ne présente pas la pureté matériel. Ceci est représenté à la nature de ZnSe évaporation comme Zn particuliers et des fluxSE2, associée à des interactions chimiques avec le Ir(BPA) substrat. L'interface est,de ce fait, composé d'une multitude de phases, les phases de Se0, ZnSe rares, réduit Se et oxydé molécules de colorant, et de Zn qui sont intercalées atomes dans leIr(BPA) substrat. PES des composites ZnSe+Ir(BPA) révèle des tendances similaires à l'Ir(BPA)/ZnSe interface. A des émissions de lumière rouge surfaciques et intermittents fanées ont été observés à partir de dispositifs qui incorporent couches alternées séquences de ZnSe et Ir(BPA) pour la couche active
Luminescent organic phases that are embedded in a conductive inorganicmatrix is proposed in this study for the active layer of a hybrid light-emitting diode. Inthis composite, the organic dye acts as the radiative recombination site for chargecarriers that are injected into the inorganic ambipolar transporting matrix. As one ofthe candidate material combinations, bilayer and composite thin films of ZnSe and ared iridium complex (Ir(BPA)) organic light emitter were prepared in situ via UHVthermal evaporation technique. The energy band alignments measured byphotoelectron spectroscopy (PES) for the ZnSe/Ir(BPA) bilayer and ZnSe+Ir(BPA)composite reveal that the HOMO and LUMO of the organic dye are positioned in theZnSe bandgap. This lineup provides the required energetic driving forces for electronand hole transfers from ZnSe to Ir(BPA). By interpreting PES data, the chemicalcomposition of the interfaces were also determined. The ZnSe/Ir(BPA) interface isreactive even though it is of high material purity. Meanwhile, the Ir(BPA)/ZnSeinterface does not exhibit material purity. This is accounted to the nature of ZnSeevaporation as individual Zn and Se2 fluxes, coupled with chemical interactions withthe Ir(BPA) substrate. The interface is, thereby, composed of an abundance of Se0phases, sparse ZnSe phases, reduced Se and oxidized dye molecules, and Znatoms that are intercalated into the Ir(BPA) substrate. PES of the ZnSe+Ir(BPA)composites reveals similar trends to the Ir(BPA)/ZnSe interface. A faded areal andintermittent red light emissions were observed from devices that incorporatedalternating layer sequences of ZnSe and Ir(BPA) for the active layer

The purpose of this thesis work is to design and fabricates organic-inorganic hetero junction White Light Emitting Diode (WLED). In this WLED, inorganic material is n- type ZnO and organic material is p-type conjugated polymer. The first task was to synthesise vertically aligned ZnO nano-rods on glass as well as on plastic substrates using aqueous chemical growth method at a low temperature. The second task was to find out the proper p- type organic material that gives cheap and high efficient WLED operation. The proposed polymer shouldn’t create a high barrier potential across the interface and also it should block electrons entering into the polymer. To optimize the efficiency of WLED; charge injection, charge transport and charge recombination must be considered. The hetero junction organic-inorganic structures have to be engineered very carefully in order to obtain the desired light emission. The layered structure is composed of p-polymer/n-ZnO and the recombination has been desired to occur at the ZnO layer in order to obtain white light emission. Electrical characterization of the devices was carried out to test the rectifying properties of the hetero junction diodes.

iv

L’application de la technologie OLED (diode électroluminescente organique) pour l’affichage est actuellement principalement portée par le marché des écrans de télévision et des smartphones. Les matériaux et les substrats utilisés permettent de produire des dispositifs légers, compacts, voire flexibles, possédant un excellent contraste image et une fréquence de rafraîchissement élevée. Les contraintes technologiques limitant l’industrialisation concernent la durée de vie des dispositifs. D’une part, les matériaux utilisés dans les structures OLEDs sont dégradés en présence d’eau et d’oxygène, il est donc essentiel de passiver le dispositif avec une structure de haute qualité barrière à l’atmosphère. D’autre part, il est nécessaire d’ajouter une protection mécanique en surface, sous forme de capot ou de protection monolithique, modulable en fonction de l’application visée. Ces travaux de thèse visent à développer une nouvelle conception de packaging, intégrant des nanocomposites organiques-inorganiques au sein de l’architecture d’encapsulation multicouche développée au CEA-LETI, et appliquée aux écrans de petite taille (microdisplays) OLED réalisés sur substrat silicium. Ces matériaux permettent de cumuler des propriétés d’ordinaire antagonistes ; celles de la phase organiques (flexible, déposable par voie liquide) et celles de la phase inorganique (barrière au gaz, résistance mécanique et chimique). Les résultats reposent sur le contrôle fin de la morphologie ; le procédé sol-gel a donc été choisi pour sa versatilité. Nous avons montré qu’il était possible de définir plusieurs formulations composites. L’une en particulier, basée sur des nanoparticules de silice intégrées dans une matrice polymère, s’est révélée compatible avec l’encapsulation monolithique des substrats OLED, permettant notamment la reprise de contact électrique. L’ajout de ce matériau au sein de l’architecture de passivation augmente la résistance barrière au gaz et, par extension, la durabilité des dispositifs en conditions climatiques sévères. Utilisé en tant que protection mécanique de surface, cette solution en couche mince n’atteint pas la résistance mécanique des capots de verre, mais permet malgré tout de protéger les substrats pendant toutes les phases de fabrication et de manipulation. L’avantage principal de cette solution packaging réside dans la diminution de l’épaisseur totale, augmentant le contraste en limitant fortement les pertes lumineuses, et ouvrant la porte aux substrats et dispositifs flexibles
Due of the ongoing growth of smartphones and TVs displays markets, the application of OLED (Organic Light Emitting Diode) technology for displays has become a major center of interest. The materials and substrates used in such architectures allow to develop lightweight, compact and even foldable displays, demonstrating an excellent image quality and fast refresh rates. Currently, the technological drawbacks restricting the exploitation on industrial scale mainly concern the lifespan of the devices. First, materials used in OLED architecture are highly sensitive to moisture and oxygen ingress and require a high barrier encapsulation. In addition, a specific protection needs to be included to secure the device from mechanical failures. As so various options from glass lids to flexible barriers are likely to be considered depending on the intended use. This work deals with the production of OLED microdisplays deposited on silicon substrates, and aims to develop an alternative packaging solution, based on organic-inorganic nanocomposite layers, both on top and embedded into the multi-barrier passivation architecture previously developed at the CEA-LETI. Synergistic properties can be obtained from composite materials, enhancing the advantages of both the organic (flexibility, processability) and inorganic phase (barrier properties, mechanical and chemical resistance). As a high control on the morphology in required, the sol-gel process was therefore selected for its versatility. Several composite materials were designed. One selected formulation, based on silica nanoparticles dispersed in a polymer matrix, proved to be fully compatible with the monolithic encapsulation of OLED circuits, including, among other properties, the recovery of the electrical bonding. Passivation architectures using the composite as interface layer showed improved barrier properties as well as an enhanced durability of devices stored in warm and damp environment. Obviously, a thin hard-coat layer does not equal a glass lid in terms of mechanical resistance, yet our formulation provided a sufficient protection during the overall process and handling of the displays. The main advantages of this alternative packaging rely on the reduced thickness, increasing the contrast by minimizing the loss of luminous efficacy through guided mode and offering the prospect of flexible substrate manufacturing

Principes de base de la methode movpe et problemes poses par sa mise en oeuvre. Cas particuliers de gainp et de algainp. Analyse des mecanismes de la methode movpe. Proprietes des interfaces gainp/gaas, algainp/gaas et algainp/gainp et presentation de puits quantiques algainp/gainp. Realisation de dispositifs optoelectroniques: presentations de diodes electroluminescentes a homojonctions en gainp et algainp, examen des travaux des principales equipes epitaxiant algainp, presentation de lasers a heterojonctions algainp/gainp/algainp

碩士
中原大學
物理研究所
105
Perovskite materials have demonstrate high power conversion ef-ficiency (> 20%) in the field of solar cells. In addition, recently, per-ovskite materials were also used for light-emitting diodes, which are important solid-state lighting device. In this work, thin film and quantum dots based on CsPbX3 were prepared and the optoelectronic characteristics of quantum dots were also investigated by using X-ray diffraction, scanning electron microscope, tunneling electron micro-scope, photoluminescence spectra and absorption spectra. We further use CsPbX3 thin film and quantum dots to realize light-emitting diodes.

碩士
國立臺灣大學
化學研究所
105
White light-emitting diodes (LEDs) is widely used as backlighting components in the modern liquid-crystal display (LCD). For high-quality backlight, color saturation and color gamut are the key indicators, which affect the color performance display devices. Perovskite CsPbBr3 quantum dots (QDs) are regarded as the most promising narrow-band green-emitting material for wide-color-gamut backlight displays because of their high photoluminescence quantum yield (PLQY) and the narrow-band emission with a full width at half maximum (FWHM) of ∼20 nm. Despite their growing popularity, CsPbBr3 QDs have several shortcomings such as the existence of surface trap states, poor thermal and aqueous stability, and the solution QDs are unsuitable for direct use in on-chip white LEDs. Here, a three-step treatment of perovskite CsPbBr3 QDs toward high brightness and stable narrow-band green emission was investigated. After the treatment, a robust and stable narrow-band perovskite mesoporous-CsPbBr3/SDDA@ PMMA powder was obtained. The powder exhibited several advantages, including high absolute PLQY of 63%, improved thermal stability, and water resistance. A white LED used in backlight display was successfully fabricated with color coordinates of (0.271, 0.232) that passed through RGB color filters with an NTSC value of 102%. Moreover, CsPbBr3 perovskite QDs are potential emitters for QLED electroluminescent displays. However, balancing their performance and their environmentally friendly property is challenging. To achieve such balance, we demonstrated an easy hot-injection method to synthesize Cs(Pb1-xSnx)Br3 QDs by partially replacing the toxic Pb2+ with the highly stable Sn4+. Meanwhile, the absolute PLQY of Cs(Pb0.67Sn0.33)Br3 QDs increased from 45% to 83% compared with CsPbBr3. Based on a femtosecond transient absorption, time-resolved PL, and single-dot spectroscopies, we conclude that the PLQY enhancement is due to the reduction of trion formation in perovskite QDs with Sn4+ substitution. This trion-formation suppression by Sn4+ substitution consequently increased the performance of QLED devices based on these highly luminescent Cs(Pb0.67Sn0.33)Br3 QDs, exhibiting a central emission wavelength of 517 nm, a current efficiency of 11.63 cd/A, and an external quantum efficiency of 4.13%, which to date are the highest values among the reported Sn-based perovskite QLED devices.

碩士
國立臺灣大學
化學研究所
106
White light-emitting diodes (LEDs) is widely used as backlighting components in the modern liquid-crystal display (LCD). For high-quality backlight, color saturation and color gamut are the key indicators, which affect the color performance display devices. Perovskite CsPbBr3 quantum dots (QDs) are regarded as the most promising narrow-band green-emitting material for wide-color-gamut backlight displays because of their high photoluminescence quantum yield (PLQY) and the narrow-band emission with a full width at half maximum (FWHM) of ∼20 nm. Despite their growing popularity, CsPbBr3 QDs have several shortcomings such as the existence of surface trap states, poor thermal and aqueous stability, and the solution QDs are unsuitable for direct use in on-chip white LEDs. Here, the surface treatment of perovskite CsPbBr3 QDs with thiocyanate salts (SCN-) toward high brightness and stable narrow-band green emission was investigated. After the treatment, a high quantum yield and stable narrow-band perovskite CsPbX3-SCN was obtained. The product exhibited several advantages, including high absolute PLQY of 94%, enhaced photoluminescence intensity, and air stability. Moreover, CsPbBr3-SCN perovskite QDs are potential emitters for QLED electroluminescent displays. However, balancing their performance and their environmentally friendly property is challenging. To achieve such balance, we demonstrated an easy hot-injection method to synthesize Cs(Pb1-xSnx)Br3 QDs by partially replacing the toxic Pb2+ with the highly stable Sn4+. Meanwhile, the absolute PLQY of Cs(Pb0.67Sn0.33)Br3 QDs increased from 45% to 83% compared with CsPbBr3. Based on a femtosecond transient absorption, time-resolved PL, and single-dot spectroscopies, we conclude that the PLQY enhancement is due to the reduction of trion formation in perovskite QDs with Sn4+ substitution. Moreover, the CsPbBr3-SCN solution that surface treatment with thiocyanate salt increased the performance of QLED devices based on these highly luminescent cesium lead halide perovsike QDs, exhibiting a central emission wavelength of 516 nm, a current efficiency of 4.2 cd/A, and an external quantum efficiency of 1.4% which is the higher values among the CsPbBr3 perovskite QLED devices.

碩士
國立臺北科技大學
分子科學與工程系有機高分子碩士班
107
All-Inorganic cesium lead bromide perovskite combine with stretchable transparent electrodes for light emitting diodes using spray-coated Silver nanowires (AgNWs) onto the stretchable Polyurethane (PU) to develop the highly conductive and transparent electrodes. The fabricated transparent electrodes were blessed with very low sheet resistance of about 0~10 ohm, high transparent (89%), and high mechanical endurance properties (100% strain sustainability). Even under 100% strain, the fabricated transparent stretchable electrode remains stable and conductive. Furthermore, it can be used on a variety of transparent electronic applications such as light emitting diodes (LEDs), solar cells, field effect transistors, pain alleviating devices. This thesis describes the blending of Poly(ethylene oxide) (PEO) and Polyvinylpyrrolidone (PVP) polymer into CsPbBr3 emitting layer with different weight ratios and their influence on surface morphology and optical properties. Addition of Poly (ethylene oxide) (PEO) and Polyvinylpyrrolidone (PVP) polymer into the CsPbBr3 (1:0.125:0.0225) films induced the prominent luminance and current efficiency and External Quantum Efficiency (EQE) enhancement higher than that of recently trending CsPbBr3-PEO based device. Incorporated PVP polymer can potentially alter the work function of Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), thereby promoting the hole injection by enhancing the energy level alignments. Perovskite emissive layer with optimized PEO and PVP (1:0.125:0.0225) engenders the luminance (3600 cd m-2), current efficiency (3.18 cd A-1), and EQE (0.824 %) at 6.5 V. On using the as-fabricated stretchable transparent electrode, luminance of 380 cd m-2 was achieved. Still there is a big room to explore the new generation stretchable optoelectronics in various fields to make innovations in energy sectors.

碩士
國立雲林科技大學
電子工程系
105
In this paper, the organic light-emitting diode structure is PET / ITO / NPB / Alq3 / LiF / Al, where NPB is the hole transport layer and Alq3 is the fluorescent green host. Since the research topic is encapsulation layer, the structure of the devices are simple. The encapsulation materials are inorganic SiO and organic polyethylene terephthalate (PET). The thermal evaporators in the lab are not linked to a glove boxes or sputtering machines. This research tried to carry out the encapsulation of SiO and polyethylene terephthalate (PET) by thermal vapor deposition to achieve a one chamber process. So that the encapsulation was completed before it comes into contact with the atmosphere. The cost and the producing time could be substantially reduced. The research teams or the industry's flexible film encapsulation usually require a sputtering machine or an atomic layer deposition method (ALD) to deposit. In the experiment of the order of organic and inorganic packaging layer, the one was encapsulated with inorganic first has a longer lifetime. The next experiment will be multi-layer stacking and then stacking with different organic/inorganic film thickness to the composition. The lifetime of the optimized device is about 105 minutes.

The work described in the thesis deals with the study of Exploration of new lanthanide based inorganic phosphors with different crystal structures. The objective of the present study is to design and synthesis of Eu3+ based narrow band red emitting, Eu2+ based broad band tunable phosphors and Europium molecular complex in order to explore the possibilities of new phosphor materials as promising candidates for white light emitting diodes (including solid state lighting (SSL)) applications and to probe their structure - composition - property correlations. Chapter 1 introduces the solid state luminescence in inorganic materials with different crystal structures and the details of the constituents of phosphor materials are discussed with special highlight on rare earth ions. The main aim and importance of the proposed work of the thesis was summarized in this chapter. Chapter 2, discusses the Eu3+ luminescence in La1.95Eu0.05W2-xMoxO9 (x = 0 – 2, insteps of 0.1) and La2-yEuyW1.6Mo0.4O9 (y = 0 – 2, insteps of 0.2). Powder XRD analysis of La1.95Eu0.05W2-xMoxO9 (x = 0 – 2, in step of 0.1) reveals a phase transition from triclinic to cubic structure with increasing value Mo6+ concentration (x ≥ 0.2). All the compositions show broad charge transfer (CT) band due to CT from O to W/Mo and red emission (due to Eu3+ ions). In order to obtain the strongest red emission, the concentration variation of Eu3+ was performed in La2-yEuyW1.6Mo0.4O9 (x = 0 – 2, in steps of 0.2). Eu1.6La0.4W1.6Mo0.4O9 composition shows high red emission intensity (~8.2 times) compared to that of commercial red phosphor with very good CIE chromaticity coordinates (x = 0.67, y = 0.33). Selected composition has also been synthesized by simple co-precipitation method. The emission intensity of the Eu1.6La0.4W1.6Mo0.4O9 phosphor, synthesized by co-precipitation technique is ~1.78 times higher than that of the one which is synthesized by solid state reaction. The phonon sideband spectrum analysis has been carried out for Eu3+ activated La2M2O9 (M = W and Mo). The temperature dependent photoluminescence studies reveals that the Eu1.4La0.6W1.6Mo0.4O9 compositions loses 30% of efficiency up to 400 K (compared to ~80% for CaS:Eu2+) and the Judd – Ofelt parameters were also calculated for Eu3+ ions. In addition, the Eu3+ concentration quenching studies also been executed in the La2M2O9 (M = W and Mo) phosphors. Chapter-3, describes the optical properties of Eu3+-substituted La2Li0.5Al0.5O4 red emitting phosphors. Powder X-Ray diffraction (XRD), diffuse reflectance spectra (DRS) and spectroflurometry were used as vital characterizing tools for the phosphors. The europium (Eu) concentration dependence luminescence properties and Judd–Ofelt intensity parameters have been investigated and calculated, respectively. All the compositions showed orange red emission (due to magnetic and electric dipole transition of Eu3+ ion) with appropriate CIE colour gamut under near UV or blue ray excitation. The calculated critical distance showed that the energy transfer occurs between Eu to Eu via exchange mechanism. Eu1.4La0.6Li0.5Al0.5O4 composition showed highest red emission intensity with CIE color saturation compared to that of commercial Eu activated yttrium oxy-sulfide red phosphor. Eu3+ activated double perovskite phosphor gained much interest due to their potential use in white LEDs. In the second part, a series of novel red emitting phosphor compositions, Ca2MgW1-xMoxO6, have been synthesized and studied their optical properties. Further, Eu3+ concentration variation was executed in Ca2MgW0.85Mo0.15O6 host lattice to gain enhanced excitation and emission properties. All the compositions show broad and intense charge transfer (CT) absorption band ranging from UV to blue region, where the near UV-LED (nUV-LED) emission occurs. The Eu3+ emission intensity of significantly improved in the solid solutions of tungstate and molybdate [Ca2MgW1-xMoxO6; x = 0 – 1 and Ca2-2yEuyNayYyMgW0.85Mo0.15O6. Selected compositions show high emission intensity (red) compared to that of Eu3+ substituted parent phases. Dominant electric dipole(ED) transition was observed for all Eu3+ activated Ca2MgW1-xMoxO6 compositions. In this structure, the Eu3+ occupies a highly distorted non– centrosymmetric site. Ca0.9Eu0.05Li0.05MgW0.85Mo0.15O6 composition shows intense red emission under NUV/blue excitation and the emission intensity is found to be ~6 times higher than that of commercial red phosphor (Y2O2S:Eu3+ Nichia) under blue excitation (465 nm). Chapter-4, describes the luminescence properties of red emitting Li3BaSrLn3-xEux(MO4)8 (Ln = Gd, La and Y, M = W, Mo) and its solid solution phosphors with stratified scheelite structure. All the compositions crystallize in the monoclinic structure with space group P2/c. Host as well as the phosphors (Eu3+ substituted compositions) show broad absorption band in the UV to near UV region, due to the oxygen to molybdenum (absorption edge ~360 nm, O2- → Mo6+) or tungsten (absorption edge ~320 nm, O2- → W6+) CT transition. The photoluminescence (PL) study of Eu3+ substituted compositions show emission at ~615 nm (due to the forced electric dipole (ED) 5D0 →7F2 transition of Eu3+ ion), which confirms that the Eu3+ ion present in the non-centrosymmetric site. In order to study the emission behaviour systematically the Judd Ofelt (J – O) spectral intensity parameters were calculated for all phosphor compositions. The CIE colour coordinate values are well harmonized with the National Television Standard Committee (NTSC) standards. The presently synthesized tungstate, molybdate and its solid solutions (selected compositions) phosphors have been used as reference for contrast between two. The entire compositions show better absorption in the near UV to blue region and emitting red light ~615 nm indicates that this phosphor may find potential application as a red phosphor for white LED. Selected phosphors show extremely high quantum yield and the same were used to integrate with near UV LED and fabricated red LED with forward bias 10mA. Chapter-5 discusses the Eu3+ activated Ln fluorides (LnF3:Eu3+ - Ln= La, Gd) nanocrsytals synthesized by hydrothermal method using 1-Butyl-3-methylimidazolium tertrafluoroborate [BMIBF4] and NH4F as fluorine precursors. In addition, LaF3 samples through a facile hydrothermal route with hexagonal structures have been synthesized via doping of trivalent rare earth (RE3+) - RE= Eu, Tb, Sm, Dy and Tm) with rod – like and perforated morphologies using NH4F as fluorine precursor. The synthesized nanocrystals (NCs) have been structurally, morphologically characterized and their optical properties have also been investigated by spectroflurometry. The XRD patterns of Eu3+ or RE3+ substituted and unsubstituted LnF3 are indexed based on hexagonal and orthorhombic crystal structure, respectively. The TEM images reveal that the NCs are well dispersed, nearly ellipsoid, with an average size of about 5 nm. The Eu3+ activated NCs show characteristics excitation and emission spectra. The emission spectra show both magnetic (5D0 - 7F1, MD) and electric (5D0 - 7F2, ED) dipole transition with appropriate CIE color co-ordinates; however, the intensity of the MD transition was found to be high, which is accordance with the local site symmetry. The LaF3:Tm3+,Sm3+ ions show the characteristic emission of Tb3+ (green) and Tm3+ (blue), respectively. In Sm3+-doped LaF3, three prominent emission peaks at 561, 597 and 641 nm were found which are belongs to 4G5/2→6H5/2, 4G5/2→6H7/2 (MD) and 4G5/2→6H9/2 (ED) transitions, respectively. The absolute quantum yield calculated for Eu3+ activated LaF3 was found to be 16.8%. Further, Judd–Ofelt calculation has been used to analyze the experimental phenomena of Eu3+ activated LaF3. Dy3+ activated LaF3 show blue and yellow and the corresponding CIE color coordinate show white light emission (CCT value 10650K). The surface functionalized nanophosphor (DBM –LaF3:Eu3+) show extremely dominant forced electric dipole transition and significant enhancement in PLQY (79.7%) was observed. The DBM-LaF3:Eu3+ integrated with InGaN LED shows red emission (under 20 mA forward biased current) with good color saturation (CIE values x = 0.6545, y = 0.3433). Chapter-6 describes the Eu2+ luminescence in silicate based host lattice. In the first part, a series of novel yellowish – orange emitting phosphor [Ca3-xMxSi2O7 (M = Eu2+)] have been synthesized by high temperature solid state reaction. The powder x – ray diffraction patterns reveals a single phase formation with excellent crystalline nature of the phases. The photoluminescence excitation and emission studies show that the Eu2+ doped phosphors show broad absorption (300 – 525 nm) and emits yellowish – orange–red spectral region. Further efforts have been made to tune the Eu2+ emission by crystal chemical isovalent substitution of Mg2+ in Ca2+ site. Compositionally induced phase transformation has been observed at y ≥ 0.25 in Ca2.985MgxEu0.015Si2O7. The yellowish – orange-red emission (y = 0) tuned to green color (y = 1) and the corresponding CIE color coordinates (x,y) are changed from (0.5647, 0.4202) to (0.3540, 0.5932). In the second part, a series of Eu2+ activated Barium orthosilicate (BaZnSiO4) were synthesized by high temperature solid state reaction. The PL excitation study of Eu2+ shows a broad absorption band in the range of 270 to 450 nm with multiple absorption peak maxima (310, 350 and 400 nm) due to 4f – 5d electronic transition. The emission spectra of all the compositions show green color emission (in the spectral region 450 – 550 nm with a peak maximum at 502 nm and a shoulder at ~490 nm) with appropriate CIE color coordinates. The two emission peaks are due to the presence of Eu2+ in two different Ba sites in the BaZnSiO4 host lattice. The energy transfer between the Eu2+ ions in BaZnSiO4 host are elucidated from the critical concentration quenching data based on the electronic multipolar interaction. All Eu2+ activated BaZnSiO4 phosphor materials can be efficiently excited in the UV to near UV region (270 - 420 nm), making them attractive candidate as green phosphor for SSL – white LEDs. Chapter-7 describes the design, synthesis and photophysical study of imidazo-bipyridyl based Eu-complexes. Three ancillary ligands based on imidazo-bipyridyl with phenyl (Ph), naphthyl (Np), triphenylamine (TPA) substitution were synthesized and secondhand to formulate the consistent europium(III) ternary complexes using thenoyltrifluoroacetone (TTA) as an anionic ligand. The complete investigation of spectroscopic, photophysical and electrochemical properties was carried out. The attained results for all the ancillary ligands and their corresponding Eu-complexes were compared with one another. All the Eu-complexes reveal a broad excitation band ranging from near UV to blue region, along with high intense emission and apposite color purity. To further understand the ligand to metal energy transfer (ET) process, the geometry of the ligand was optimized and the energy level location (singlet and triplet) was calculated, by using DFT and TD-DFT calculations. On the basis of the theoretical calculation, the ET mechanism was proposed. From PL emission spectra in solid state, complete ET occurs from Ph, Np based ancillary ligands to Eu3+ ion, which yield a pure red emission, whereas the TPA functionalized based Eu complex show incomplete ET. Fortunately, white emission was observed in the TPA based Eu complex in the solid state. The white LED was fabricated by using a white emitting complex integrated with 395 nm emitted LED (InGaN) chips under 20 mA forward-bias current. The excitation source from LED was fully observed by the complex shown for 3Eu and showed yellowish emission in different concentrations (the similar observation also reflected in solid). However, in the case of 1Eu and 2Eu complexes, they showed close to white emission. The CIE chromaticity coordinates are close to the NTSC standard value for white emission, and in addition, the complex 3Eu coated with the blue LED chip (460 nm) by PMMA (1:10) showed bright white emission with CIE x, y value 0.30, 0.33; respectively. Chapter- 8 describes the design, synthesis and photophysical study of carbazole functionalized imidazobipyridyl based Eu-complexes. Two new ligands based on the imidazo-bipyridyl moiety were synthesized and used to synthesize EuIII-containing ternary complexes using 4,4,4-trifluoro-1-(2-thienyl)-1,3butanedione as an anionic ligand. The EuIII-containing complexes exhibit broad excitation bands in the near-UV-to-blue region of the electromagnetic spectrum, intense emissions, and color purity. To study the energy-transfer process, efforts were made to optimize ligand geometry and locate the exact position of energy levels using density functional theory and time-dependent density functional theory (confirmed experimentally). Based on the calculations, a mechanism of energy-transfer was proposed. The thermal stability of the complexes was found to be good (>250 °C). Temperature-dependent emission studies indicated that the carbazole-functionalized Eu complex is relevant to temperature sensing. The complexes were combined with an InGaN light-emitting diode (395 nm) chip, and the emission profiles under a 20 mA forward-bias current were analysed, show nearly white emission. The results indicate that the complexes reported here have the potential to be used as red-emitting components in warm-white lightemitting diodes. In addition, selected ligand (L-CBZ) and its Eu-complex (Eu(TTA)3CBZ), have been used to fabricate the OLED device. Overall, the optimized OLED device fabricated with ligand shows a ηp, ηc and external quantum efficiency (EQE) of 0.7 lm/A, 2.1 cd/A and 0.5 % at brightness of 100 cd/m2, with a maximum luminance of 2,118 cd/m2. Furthermore, for the Eu-complex, the OLED device fabricated with a 7.5 wt% emitter doped in the bipolar CBP matrix shows a best electroluminscent performance with an ηp, ηc and EQE of 0.3 lm/A, 0.99 cd/A and 1.8 % at 100 cd/m2, along with maximum luminance of 1,077 cd/m2. Chapter- 9 deals the summary and conclusion as well as future perspective of the work. The present thesis works deals with rational design and synthesis of new and novel class of Eu3+/2+ based phosphors for white LEDs applications. In addition, Eu molecular complexes also been explored for white LED or OLED applications. The observations and the conclusions derived from the present investigations are summarized in this chapter.

博士
國立臺灣大學
化學工程學研究所
102
In our research, development of encapsulating material of light emitting diodes (LEDs) is the mainly purpose. In the first part (Chapter 2), optical hybrid materials with high refractive index were synthesis by in-situ production of titanium dioxide (TiO2) directly in a commercial-grade silicone resin via a sol-gel reaction. The optical transparency of the prepared TiO2/silicone hybrid film was investigated by UV-visible spectroscopy. These hybrid films with various TiO2 contents exhibited different refractive indices; the refractive index could reach 1.66 for the hybrid with 30 wt% of the TiO2. In addition, refractive index, thermal stability of the cured hybrid materials was also investigated. In the second part (Chapter 3), novel ZrO2/silicone hybrid materials (ZrO2/AB) useful for the encapsulation of light-emitting diodes (LEDs) are synthesized by an in situ sol-gel reaction of zirconium propoxide directly in a commercial-grade silicone resin by an in situ sol-gel reaction. By the chelation of the acetic acid, the ZrO2/AB hybrids exhibit high transparency owing to the well-dispersed ZrO2 particles in the silicone material, and their refractive index value also increased with increasing weight percentage of the ZrO2 in the hybrid. These high-refractive-index ZrO2/AB hybrids were then used as encapsulating materials to improve the luminous flux of the LEDs. From the results of the luminous flux measurement, the LED encapsulated with the pure silicone material has luminous flux of 3.97 lm. After encapsulated with the ZrO2/AB hybrid, the luminous flux of the LED was enhanced to a value of 4.35, which revealing that the increase in the refractive index of the encapsulating material by the incorporation of the ZrO2 could effectively improved the luminous flux of the LED, and these novel ZrO2/AB hybrids could also be considered as a suitable candidate as the encapsulating material for the LED. In the third part (Chapter 4), ZrO2 particles are synthesized directly in a commercial-grade silicone resin (AB) with the addition of a vinyl monomer (glycidyl methacrylate, GMA) by an in situ sol-gel reaction to obtain the silicone hybrid material (ZrO2/ABG). In addition to use the acetic acid as chelating agent, the addition of the GMA is able to retard the gelation rate of the metal alkoxide compound as well as the growing rate of ZrO2 during the sol-gel reaction, and also enhance the interfacial strength of the inorganic fillers with the silicone matrix by reacting with the silicone resin through a hydrosilation reaction via its vinyl group. The ZrO2/ABG hybrids thus exhibit excellent transparency and high refractive index. These ZrO2/ABG hybrids were then used as encapsulating materials to help the LEDs reach a higher luminous flux. Furthermore, according to the optical theory and the structure of the high-power LEDs, a simple simulation model was developed to estimate the luminous flux of the LEDs encapsulated with the ZrO2/ABG hybrids and the influence of the refractive index of the passivation layer on the luminous flux of the LEDs. Finally, with the help of this simulation model, an optimum combination of the encapsulating material and the passivation layer with appropriate refractive index values was obtained for achieving the highest luminous flux of LED. In the fourth part (Chapter 5), the purpose is to improve thermal mechanical property of the encapsulating materials in a very large temperature difference condition., thus decreasing the influence of the encapsulation on the reliability performance of the LED. The PBA(polybutylacrylate) oliogomer was firstly synthesized by a telomerization using 2-mercaptoethanol as a chain transfer agent. By the absorption to the inorganic particles and the carbonyl groups, the ZrO2 particles were produced on the oligomer chains of the PBA via an in situ sol-gel reaction to obtain the ZrO2-PBA composite particles, and subsequently mixed with a commercial-grade silicone resin to obtain the ZrO2-PBA/silicone hybrid materials (ZrO2-PBA/AB). The well-dispersed ZrO2-PBA domains lead to a high transparency and high refractive index of the ZrO2-PBA/AB hybrids, resulting in a higher luminous flux than the pristine silicone material. In addition to discuss the transmittance, refractive index, thermal resistance, and the water uptake of the ZrO2-PBA/AB hybrids, thermal stress evaluation of the LEDs encapsulated with the ZrO2-PBA/AB hybrids was also carried out in a thermal shock experiment with a temperature change from -35 °C to 125 °C within 15 mins. The results show that these ZrO2-PBA/AB hybrids have a lower thermal stress and exhibit a better mechnical resistance against the thermal shock, and the reliability performance of the LEDs are also greatly improved as encapsulated with the ZrO2-PBA/AB hybrids.

碩士
國立成功大學
微電子工程研究所碩博士班
100
In this study, the color conversion organic light-emitting diodes (OLEDs) were fabricated by using the blue-green OLEDs and red emitting CdSe/ZnS core/shell quantum dots (QDs). The basic structure of the OLEDs was composed by indium tin oxide (ITO)/ N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-1,1′ biphenyl)-4,4′-diamine (NPB)/ 2-methyl-9,10- di(2-napthyl)anthracene:p-bis(p-N,N-diphenyl-aminostyryl)benzene (MADN:DSA-Ph)/ tris-(8-hydroxyquinoline)aluminum (Alq3)/ lithium fluoride (LiF)/ aluminum (Al). All of the devices were deposited on glass substrates. NPB, MADN:DSA-Ph, Alq3, LiF, and Al were used as the hole transporting layer, emitting layer, electron transporting layer, electron injection layer and cathode, respectively. To improve the light emitting efficiency of our blue-green emitting devices, the microcavity OLEDs consist of the semi-transparent silver (Ag) thin film as the bottom mirror and Al film as the top mirror was fabricated. Besides, the molybdenum trioxide (MoO3) thin film could be well-deposited on the Ag film by thermal evaporation, result in the enhancement of light emitting efficiency and decreaseing the turn on voltage for microcavity OLEDs. Finally, the QD-PMMA composite film was wiped on the backside of the glass substrates to be used as the color conversion layer. The red emitting QDs were successfully excited by blue-green light emitting devices and the pure white organic light-emitting diodes (WOLEDs) were achieved by introducing the intensity adjustment of the three-band spectra. Both WOLEDs showed high color stability, despite the increase of the operation current. WOLEDs with microcavity structures also exhibited higher light efficiency. Nevertheless, the pure white light wasn’t easily obtained. The luminous efficiency and luminance was 1.93 cd/A and 9904 cd/m2 at 6 mA, respectively, which was enhanced by 42.9 % and 64 % in comparison with that of 1.35 cd/A and 6047cd/m2 for WOLEDs based on basic structures, respectively. The CIE coordinates were (0.306, 0.323), and the correlated color temperature (CCT) was 6910.

碩士
國立臺北科技大學
分子科學與工程系有機高分子碩士班
106
The formation of high-quality dense CsPbBr3 perovskite thin films by employing polyethylene oxide (PEO) dielectric polymer matrix and a organic molecule moieties (TPBi). A simple facile spin coating based method is developed to obtain high quality CsPbBr3 emitting layers with low defects by mixing different weight ratio between PEO:TPBi and CsPbBr3 in the premixed solutions. Presence of PEO matrix facilitated CsPbBr3-PEO films with high surface coverage, especially the film synthesized with CsPbBr3:PEO 1:0.09 weight ratio appeared exceptionally smooth without large crystallites. The results displayed on SEM and AFM images. Pure CsPbBr3 perovskite device exhibits very low luminance and EQE (363 cd m−2 and 0.01%). CsPbBr3:PEO 1:0.09 film based device exhibits a peak luminance and EQE of 3500 cd m−2 and 0.11% at 5.1 V. While the Addition of TPBi, into the CsPbBr3-PEO (1:0.09) films induced the prominent luminance and EQE enhancement (approximately 10-fold increase) higher than that of recently trending CsPbBr3-PEO based device. The TPBi based optimized device harvested exceptionally high luminance of 6800 cd m−2 and EQE of 0.25% at 6 V. This work highlights that the film quality is not only a key factor to promote the luminescence in CsPbBr3, but it also pays some significant contribution to achieve higher performance on Perovskite LEDs and also applied in touch response device.

碩士
國立交通大學
光電工程研究所
106
The advantages of perovskite quantum dots (QDs) include low cost, easy fabrication and high luminescent efficiencies. In this thesis, we used emulsion synthesis technique, which is convenient and versatile for the production of CH3NH3PbBr3 QDs at room temperature. We blended polyethylene glycol (PEG) in the perovskite light-emitting layer, in with PEG were used to reduce the injection of electrons. After blending PEG, the device (QDs:PEG=1:1, 2.5 mg/mL) exhibited the highest brightness and current efficiency. The brightness was increased by 160 times, and the current efficiency was significantly improved from 0.000257 to 1.06 cd/A.

碩士
逢甲大學
化學工程學系
104
Polysiloxane based organic-inorganic hybrid (O-I hybrid) encapsulants with high transparency, high refractive index, and thermal resistance were prepared by the sol-gel and UV curing reaction. The chemical structures of the encapsulants were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) and Si29 NMR. The effects of chemical structure on the refractive index, surface hardness, thermal resistance, and transmittance of encapsulants were investigated through refractometer, nanoindenter, thermogravimetric analysis, and UV/Vis spectrometer. In the second part, graphene was mixed with UV-curable encapsulant to prepare the composite material .The O-I hybrid oligomer encapsulants with and without graphene were mixed with phosphor, and photoinitiator. The mixture was coated on InGaN devices and UV-cured to fabricate white light emitting diodes (WLEDs). The optical, mechanical, and thermal properties of the encapsulants can be tuned by changing their chemical structures. The O-I hybrid materials are encapsulants with high refractive index (n=1.56), good transparency and thermal resistance. After being baked at 150 oC for 48h, the transmittance of encapsulant at 470 nm wavelength decreased from 87% to 86%. Effects of encapsulants on the performance of white light emitting diodes were measured. After continuous lighting, the changes in surface temperature, luminous efficiency, color rendering index, the Commission Internationale de l’Éclairage coordinates, and correlated color temperature (CCT), were investigated to evaluate the stability of the WLED. The WLED surface temperatures of V7g10r1, V7g10r1.5, and V7G4g10r1.5 were 47.5, 46.4, and 44.4℃, respectively. The luminous efficiency, color rendering index, and CCT of V7g10r1 WLED are 130 lm/W(20mA), 84.1, and 4951 K, respectively. After continuous lighting for 20 days, the luminous efficiency, color rendering index, and CCT of V7g10r1 WLED are 113 lm/W(20mA), 82.9, and 4772 K, respectively. For the V7g10r1.5 samples without graphene, the luminous efficiency, color rendering index, and CCT of V7g10r1 WLED are 97.3 lm/W (20mA), 89.8, and 4653 K, respectively. After continuous lighting for 10 days, the luminous efficiency, color rendering index, and CCT of V7g10r1 WLED are 91.5 lm/W (20mA), 86.8, and 3983 K, respectively. For the encapsulants with graphene, the luminous efficiency, color rendering index, and CCT of V7G4g10r1 WLED are 90.1 lm/W (20mA), 89.5, and 4555 K, respectively. After continuous lighting for 10 days, the luminous efficiency, color rendering index, and CCT of V7G4g10r1 WLED are 89.5 lm/W (20mA), 89.2, and 4566 K, respectively. Incorporation of graphene helps to improve the stability of WLED.

High brightness inorganic LEDs have been utilized effectively for signage application using the edgelighting technique. In this thesis. the inorganic LED-based edgelit signage using transparent acrylic has been evaluated. We determine that the edgelighting technique, although superior in efficiency to other available techniques, suffers from intrinsic limitations, particularly in terms of illumination uniformity. The illumination uniformity can be improved by external means such as a diamond grating. In order to quantitatively establish this, the illumination uniformity of the LED-based signage with and without the diamond grating is examined. The results show a considerable improvement in the illumination uniformity when a diamond grating is used. However, the high cost of the diamond grating and the transparent acrylic amplify the overall cost of signage using LEDs. Therefore, a distributed light source, which can eliminate the use of the diamond grating. is determined to be more suitable for signage application. Organic Light-Emitting diode (OLED), which is a distributed light source, emerges as a possible contender. The second part of our research focuses on the application of OLEDs for signage. We examine two OLED modules from different manufacturers for our evaluation. The first module is a prototype module obtained from the National Research Council (NRC) and the second module is a commercially available OLED from RiT Display Corporation. We present novel design techniques that can be used to implement signage based on OLEDs. A prototype tiled OLED display using commercially available OLEDs is designed and tested. Our investigation suggests that good light uniformity in signage panels can be achieved using OLED modules in the form of tiles. This proves that OLEDs are superior to conventional light-emitting diodes as light sources for signage in terms of illumination uniformity. However, we determine that the currently available OLEDs have a lower light-conversion efficiency in addition to higher costs when compared with conventional LEDs. Though the individual OLEDs cost more than LEDs. signage panels based on OLEDs can be made cheaper by avoiding the use of acrylic sheet and diamond grating. Moreover, the light weight of OLEDs and the fact that OLEDs are diffused sources (rather than point sources like LEDs) add an additional advantage. Also. OLEDs have the potential to be built inexpensively on flexible substrates by using the roll-to-roll technique. This makes OLEDs superior to conventional LEDs in large-area signage applications.

Defect passivation and surface modification of perovskite semiconductors play a key role in achieving highly efficient and stable perovskite solar cells (PSCs) and light-emitting diodes (LEDs). This dissertation describes three novel strategies for such defect passivation and surface modification. In the first strategy, we demonstrate a facile approach using inorganic perovskite quantum dots (QDs) to supply bulk- and surface-passivation agents to combine high power conversion efficiency (PCE) with high stability in CH3NH3PbI3 (MAPbI3) inverted PSCs. This strategy utilizes inorganic perovskite QDs to distribute elemental dopants uniformly across the MAPbI3 film and attach ligands to the film’s surface. Compared with pristine MAPbI3 films, MAPbI3 films processed with QDs show a reduction in tail states, smaller trap-state density, and an increase in carrier recombination lifetime. The strategy results in reduced voltage losses and an improvement in PCE from 18.3% to 21.5%, which is among the highest efficiencies for MAPbI3 devices. The devices maintain 80% of their initial PCE under 1-sun continuous illumination for 500 h and show improved thermal stability. In the second strategy, we reduce the efficiency gap between the inverted PSCs and regular PSCs using a trace amount of surface-anchoring, long-chain alkylamine ligands (AALs) as grain and interface modifiers. We show that long-chain AALs suppress nonradiative carrier recombination and improve the optoelectronic properties of mixed-cation mixed-halide perovskite films. These translate into a certified stabilized PCE of 22.3% (23.0% PCE for lab-measured champion devices). The devices operate for over 1000 hours at the maximum power point (MPP), under simulated AM1.5 illumination, without loss of efficiency. Finally, we report a strategy to passivate Cl vacancies in mixed halide perovskite (MHP) QDs using non-polar-solvent-soluble organic pseudohalide (n-dodecylammonium thiocyanate (DAT)), enabling blue MHP LEDs with enhanced efficiency. Density-function-theory calculations reveal that the thiocyanate (SCN-) groups fill in the Cl vacancies and remove deep electron traps within the bandgap. DAT-treated CsPb(BrxCl1-x)3 QDs exhibit near unity (~100%) photoluminescence quantum yields; and their blue (~470 nm) LEDs are spectrally stable with an external quantum efficiency (EQE) of 6.3% – a record for perovskite LEDs emitting at the 460-480 nm range relevant to Rec. 2020 display standards.

The International Energy Agency estimated that lighting accounts for ~19% of the total worldwide energy consumption. Light emitting diodes (LEDs) have higher efficiency compared to that of conventional lighting sources. The commercial white-LEDs (WLEDs) are based on broad-band Y3Al5O12:Ce3+ (YAG:Ce) yellow phosphor in combination with blue LED chips through a low cost and simple procedure, in which the YAG:Ce phosphor is directly packed on the blue InGaN chip. However, such two colour-based WLEDs exhibit poor colour rendering index (CRI, usually <75), high correlated colour temperature (CCT, >6500 K), and chromaticity drifts, which cannot fully satisfy the applications of lighting and backlighting of the displays. Also, LEDs still face some other drawbacks such as the relatively low efficient green emission, termed the ³green gap´ issXe. A promising alternative strategy is based on the downshift of the electroluminescence of near ultra-violet (NUV)/blue LEDs into the green spectral region by UV/blue-down shifting phosphors. Thus, novel efficient white and green-emitting materials for the phosphor-converted LED applications are required. In this thesis, organic-inorganic hybrids (ureasils, d-U(600)) doped with green emitting Tb3+-based complexes were applied in combination with NUV-LED chips to fabricate efficient green LED prototypes. To improve CRI and CCT of commercial WLEDs, novel blue-light excited La2Ce2O7:Eu3+ red phosphors were also successfully synthesised and characterized. Moreover, tuned white light emitters involving d-U(600) hybrids doped with lanthanide (Ln3+=Tb3+, Eu3+)-based complexes, fluorescent dyes (e.g. coumarin), and carbon dots were also prepared and optically characterised revealing intriguing CCT, CRI and photostability towards novel WLEDs.
A Agência Internacional de Energia estimou que o sector de iluminação representa cerca de 19% do consumo total de energia mundial. Os díodos emissores de luz (LEDs) têm maior eficiência em comparação com as fontes de iluminação convencionais. Os LEDs brancos comerciais (WLEDs) são baseados na combinação de LEDs azuis baseados em InGaN com o luminóforo Y3Al5O12:Ce3+ (YAG:Ce). Este material, que é um emissor de banda larga na região espectral do amarelo. é depositado de forma simples e a baixo custo sobre o LED azul. No entanto, a emissão deste WLEDs baseia-se na adição de duas cores tendo um índice de reprodução de cor baixo (CRI, geralmente <75), elevada temperatura de cor (CCT, > 6500 K) e variação de cromaticidade, que são claras desvantagens em aplicações de iluminação e retroiluminação. Para além destas desvantagens, estes LEDs ainda apresentam emissão na região do verde relativamente menos eficiente (usualmente designado em linguagem inglesa como ³green gap issue´). Uma estratégia alternativa a estes LEDs baseia-se na utilização de dispositivos emissores nas regiões espectrais do ultravioleta próximo (NUV) e do azul combinados com um material capaz de desviar esta emissão para a região do visível. Assim, novos materiais emissores eficientes quer de luz verde quer de luz branca para as aplicações em LEDs são necessários. Nesta tese, híbridos orgânicos-inorgânicos (ureasils, d-U(600)) dopados com complexos à base de Tb3+ emissores no verde foram combinados com NUV-LED comerciais para fabricar protótipos de LED verdes eficientes. Para melhorar o CRI e CCT dos WLEDs comerciais, novos luminóforos de La2Ce2O7:Eu3+ com emissão no vermelho e excitados com LEDs azuis foram, também, sintetizados e caracterizados. Na parte final da tese discute-se a contribuição de novos materiais emissores de luz branca sintonizável baseados em híbridos d-U(600) dopados com complexos de iões lantanídeos (Ln3+=Tb3+, Eu3+), corantes fluorescentes e pontos de carbono com propriedades óticas (CCT, CRI e fotoestabilidade) melhoradas, face ao estado da arte.
Programa Doutoral em Ciência e Engenharia de Materiais

Controlled patterning of light emitting diodes on semiconductors enables a vast variety of applications such as structured illumination, large-area flexible displays, integrated optoelectronic systems and micro-total analysis systems for real time biomedical screening. We have demonstrated a series of techniques of creating quantum-based (QD) patterned inorganic light emitting devices at room temperature on silicon (Si) substrate. In particular: (I) A combination of QDs self-assembly and microcontact printing techniques were developed to form the light emission monolayer. We expand the self-assembly method with the traditional Langmuir-Schaeffer technique to rapidly deposit monolayers of core: shell quantum dots on flat substrates. A uniform film of QDs self-assembled on water was transferred using hydrophobic polydimethylsiloxane stamps with various nano/micro-scale patterns, and was subsequently stamped. A metal oxide electron transport layer was co-sputtered onto the QDs. The structure was completed by an e-beam evaporating thin metal cathode. Multicolor light emission was observed on application of voltage across the device. (II) We also demonstrate the photolithographic patterning capability of a metal cathode for top emitting QDLEDs on Si substrates. Lithographic patterning technique enables site-controlled patterning and controlled feature size of the electrode with greater accuracy. The stability of inorganic silicon materials and metal oxide based diode structure offers excellent advantages to the device, with no significant damage observed during the patterning and etching steps. Efficient electrical excitation of QDs was demonstrated by both the methods described above. The technique was translated to create localized QD-based light sources for two applications: (1) Three-dimensional scanning probe tip structures for near field imaging. Combined topographic and optical images were acquired using this new class of “self-illuminating” probe in commercial NSOM. The emission wavelength can be tuned through quantum-size effect of QDs. (2) Multispectral excitation sources integrated with microfluidic channels for tumor cell analyses. We were able to detect the variation of sub-cellular features, such as the nucleus-to-cytoplasm ratio, to quantify the absorption at different wavelength upon the near-field illumination of individual tumor cells towards the determination of cancer developmental stage.
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Solution deposition of thin film photovoltaic materials leads to large variations in the morphological and chemical compositions of the film. In order to improve device functionality, it is important to understand how morphology and chemical composition affects charge generation, separation, and collection. This PhD work will first study bulk methods in order to characterize materials in solution and films. The results are then correlated with microscopy studies examining morphology. Other methods used in this PhD work will directly couple spectra and microscopy. Microscopic regions of such films and devices can be illuminated using scanning confocal microscopy or near-field scanning optical microscopy (NSOM), which allows for one to directly probe regions of the film at or below the optical diffraction limit. By scanning the sample over a fixed laser spot we can simultaneously create image maps of the topographical, electrical and optical properties. This technique, known as laser beam induced current (LBIC) allows one to directly probe a local area of a device with 100-300nm resolution. Along with bulk device efficiency studies, near field and confocal data of inorganic and organic materials are investigated. These include devices fabricated with a blend of P3HT (poly[3-hexylthiophene]) and perylene diimide derivatives, and Cu(InxGa1-x)Se2 [CIGS] nanoparticle devices. Finally, we use a new device architecture, a lateral organic photovoltaic (LOPV) in order to spatially resolve transport in functional organic devices.
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碩士
國立交通大學
光電工程研究所
106
Organic-inorganic hybrid perovskites are recognized as a promising candidate for photovoltaic applications. More recently, this emerging type of perovskite materials also becomes highly attractive as active materials for other optoelectronic devices, including lasers, light-emitting diodes (LEDs) and photodetectors. The aim of this thesis is to develop high-performance LEDs based on solution processes. We have found the efficiency of photoluminescence (PL) of CH3NH3PbBr3 thin films can be enhanced after post-deposition surface treatments with bidentate chelating ligands, including 1,10-phenanthroline, 4,4'-bipyridine and 4,7-diphenyl-1,10-phenanthroline (Bphen). The PL intensities of were improved significantly after we spin-coated 1,10-phenanthroline and 4,4'-bipyridine on the thin film surfaces. Meanwhile, the treatments also resulted prolonged PL lifetimes, suggesting the passivation of the defects in the perovskite thin films. The unsaturated or under-coordination Pb ions, which are also Lewis acids, has been considered as one of the origins of the electronic traps in perovskite thin films. Therefore, the chelating ligands, which behaved as Lewis bases, could effectively react with the Lewis acids and passivate the defects. The morphologies of the perovskite films were also examined using X-ray diffraction, atomic force microscopy, and scanning electron microscopy; the results indicated that the surface treatments did not significantly affect the films. Moreover, the lower defect densities, which were deduced from the current-voltage curves of the hole-only devices, after the treatments supported the functions of the above ligands. Finally, perovskite LEDs were fabricated and the device passivated with 1,10-phenanthroline exhibited a nearly doubled quantum efficiency. We anticipate that this approach proposed in this thesis could lead to a general method for improving the PL efficiencies and the device performance.

碩士
國立臺東大學
應用科學系
105
The development of light-emitting diodes has changed the way of life today, the replacement of light bulb and other traditional light source. The scope of application covers lighting systems, backlight, display systems and mobile devices, has been hailed as the twenty-first century The most watched technology. QLED (Quantum Dot Light-emitting diode), which has a narrow half-width, high-purity purity quantum dot technology. It will be a new wave of displays in the future when pursuing high-quality, high-performance displays. Perovskite CsPbX3 (X = Cl, Br, I) was synthesized by chemical hot injection method using colloidal solution as the inorganic luminescent layer. Color of green CsPbBr3 to red CsPbBrxI (3-x) can be synthesized by regulating the different proportions of Group VII A anions; and green CsPbBr3 to blue CsPbCl(3-x) Brx, which covers the color of all visible spectral regions. The inorganic lead halide perovskite quantum dots solution is purified to obtain a very narrow half width (FWHM, Full width at half maximum). In this study, we synthesized four color quantum dots, its half width and width blue: 16.6 nm blue and green: 17.4 nm green: 21.4 nm orange: 25.6 nm. Which is very narrow compared to the CdSe quantum dots material; it also has better color purity for the phosphor material. And then inorganic lead halide perovskite quantum dots made of components of the performance of light color, and the solution is very close to the fluorescent position. Although a little shift, speculation is affected by the other layers of the component, but still can be used to determine the wavelength of the solution fluorescent light color components. In the production of components, our team to the whole fabrication as the goal of development. In this study, in addition to the synthesis of light-emitting layer of inorganic lead halide perovskite quantum dots also contains the element of the electron injection layer of zinc oxide nanoparticles. However, the size of zinc oxide nanoparticles determines the energy gap. This paper provides a method for the synthesis of different sizes of zinc oxide nanoparticles. Small size of zinc oxide nanoparticles with energy gap at 3.32 eV~7.1 eV, Big size of zinc oxide nanoparticles with energy gap at 3.52 eV~7.0 eV. It can be found that the smaller the particle size, the lower the energy gap contributes to the electron injection of the cathode. As the hole blocking layer more effectively block the loss of holes, so the smaller the particle size of the components of the efficiency can be improved. This work established three different parameter sets for the production of zinc oxide nanoparticles. Can match the different luminescent layer material with the appropriate zinc oxide nanoparticles, so that components have better efficiency. In the QLEDs with zinc oxide nanoparticles and inorganic lead halide perovskite quantum dots by type IV structure with organic hole- and inorganic electron-transport layers. With the support of very few papers, QLEDs successful release of green light. Even the brightness is only 60 cd/m2. There is still a long distance away from becoming a product, but it is definitely a very promising outcome.

博士
國立中央大學
電機工程研究所
91
Abstract The Si-based metal-semiconductor-metal photodetectors (MSM-PDs) had been extensively studied to improve their performances. Firstly, the effects of trap-states in a composition-graded intrinsic hydrogenated amorphous silicon-germanium (i-a-Si1-xGex:H) film on MSM-PDs’ performances were studied. The experimental results indicated that the fall time of the device transient response could be reduced significantly by employing the i-a-Si1-xGex:H layer. Secondly, the higher dark-current temperature-dependence for trench-electrode Si-based MSM-PD having an i-a-Si:H dark-current suppressing layer had been studied and improved. The poor dark-current temperature-dependence could be improved significantly by reducing the trap-states in the depletion region of the reverse-biased crystalline/amorphous Si heterojunction. Thirdly, an one-mask self-aligned technique was successfully used to fabricate trench (U-grooved)-electrode Si-based MSM-PDs. Only one photolithography mask was needed during fabrication and could drastically facilitate this device to be integrated with other devices. At last, the a-Si:H/a-SiC:H (hydrogenated amorphous silicon carbide) multi-layers were employed to enhance the sensitivity of a MSM-PD. By employing the a-Si:H/a-SiC:H multi-layers, the device dark-current could be suppressed drastically and hence when the device was illuminated under a very weak incident light power (0.5μW), the device photo to dark current ratio ( under 4 V bias voltage) could be 103 times higher than that of conventional one. Also, in order to investigate the feasibility of combining polymer and inorganic films for LED fabrication, the inorganic p-a-Si:H (or p-a-SiC:H) / n-a-SiCGe:H layers were employed as hole/electron injection layers (HILs/EILs) in the MEH-PPV polymer LEDs (PLEDs). By employing the amorphous HIL/EIL, the PLED’s threshold voltage could be reduced and brightness could be enhanced.

博士
國立成功大學
化學工程學系
103
Silver nanowire (Ag NW)/inorganic semiconductor composite films and gallium nitride (GaN) films were fabricated for the application of organic light emitting diode (OLED) devices. The Ag NW ink was prepared using a simplified polyol method. After synthesis, a reusable porous membrane was utilized to purify the Ag NW solution. Nearly 90% of silver nanoparticles (Ag NPs) could be removed. In order to increase the conductivity of Ag NW films, antimony tin oxide (ATO) nanoparticles were added to form composite films. By emitting infrared (IR) light for 30 sec, the sheet resistance of the composite film could be decreased to 34 ohm/sq with a light transmittance of 91%. For the OLED devices using composite films as anodes, the maximum luminance and efficiency could reach 7020 cd/m2 and 2.7 cd/A, respectively, which was better than that of the device with indium tin oxide (ITO) anode. Next, the growth of GaN (0002) films deposited on sapphire substrates by inductively coupled-plasma (ICP)-enhanced reactive magnetron sputtering was investigated. X-ray diffraction (XRD) measurements confirmed that the high quality GaN crystallites could be obtained at a temperature as low as 500°C. The N:Ga ratio of the film grown at 500°C was almost 1:1. Afterwards, the crystalline GaN film was applied to the OLED device as a carrier transporting layer. The hybrid OLED that could be operated at high voltage showed the improved device durability. The maximum luminance of the hybrid OLED was 3451 cd/m2, higher than that of the conventional device.

碩士
國立交通大學
影像與生醫光電研究所
107
All-inorganic perovskites such as CsPbX3 (X=Cl, Br, I) are less susceptible to moisture and oxygen than organic-inorganic hybrid perovskites. With such chemical stability and excellent optical properties, e.g. narrow spectral width and adjustable emission wavelength, it has attracted much attention for optoelectronic applications. In this thesis, we focus on the CsPbBr3 light-emitting diode, and try to simplify the fabrication processes–a nearly fully coating processes. More specifically, ZnO nanoparticles dispersed in Propylene glycol methyl ether acetate (PGMEA, obtained from TWNC) were spin-coated on top of the emission layer of CsPbBr3, serving as an electron transport layer. The experimental results show that this method does not damage the CsPbBr3 film surface, thereby improving the survival time of device and reducing current value. Finally, by adjusting the concentration and dispersed solvent of CsPbBr3 and the speed of ZnO nanoparticle spin coating to optimize the fabrication parameters, the devices with the relatively higher external quantum efficiency were obtained.