<p> Organic Light Emitting Diodes (OLEDs) are extremely attractive candidates for flexible display and lighting panels due to their high contrast ratio, light weight and flexible nature. However, the materials in an OLED get oxidized by extremely small quantities of atmospheric moisture and oxygen. To obtain a flexible OLED device, a flexible thin-film barrier encapsulation with low permeability for water is necessary. </p><p> Water permeates through a thin-film barrier by 4 modes: microcracks, contaminant particles, along interfaces, and through the bulk of the material. We have developed a flexible barrier film made by Plasma Enhanced Chemical Vapor Deposition (PECVD) that is devoid of any microcracks. In this work we have systematically reduced the permeation from the other three modes to come up with a barrier film design for an operating lifetime of over 10 years. </p><p> To provide quantitative feedback during barrier material development, techniques for measuring low diffusion coefficient and solubility of water in a barrier material have been developed. The mechanism of water diffusion in the barrier has been identified. From the measurements, we have created a model for predicting the operating lifetime from accelerated tests when the lifetime is limited by bulk diffusion. </p><p> To prevent the particle induced water permeation, we have encapsulated artificial particles and have studied their cross section. A three layer thin-film that can coat a particle at thicknesses smaller than the particle diameter is identified. It is demonstrated to protect a bottom emission OLED device that was contaminated with standard sized glass beads. </p><p> The photoresist and the organic layers below the barrier film causes sideways permeation that can reduce the lifetime set by permeation through the bulk of the barrier. To prevent the sideways permeation, an impermeable inorganic grid made of the same barrier material is designed. The reduction in sideways permeation due to the impermeable inorganic grid is demonstrated in an encapsulated OLED. </p><p> In this work, we have dealt with three permeation mechanisms and shown solution to each of them. These steps give us reliable flexible encapsulation that has a lifetime of greater than 10 years.</p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 1204. Adviser: Keh-Yung Cheng. Includes bibliographical references (leaves 83-90) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3196. Adviser: Ilesanmi Adesida. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4723. Adviser: Joseph W. Lyding. Includes bibliographical references (leaves 140-149) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Lehigh University, 2009. / Adviser: G. S. Cargill.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6611. Adviser: Kyekyoon (Kevin) Kim. Includes bibliographical references (leaves 106-117) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6646. Adviser: Ilesanmi Adesida. Includes bibliographical references (leaves 99-106) Available on microfilm from Pro Quest Information and Learning.

<p> Molecular doping of organic semiconductors is becoming exceedingly important and has led to significant commercial developments in organic electronics, since it allows to overcome performance deficiencies and material limitations. </p><p> Increasing attention has recently been placed on using very low concentrations of dopants to eliminate the effect of gap states in organic semiconductors, in order to improve carrier mobility, adjust the energy level alignment at interfaces, and achieve overall better device performance. However, direct spectroscopic observations and quantitative analyses have not been done yet to study the impact of dopants on the density of states of organic semiconductors. Here, by using a combination of electron spectroscopy and carrier transport measurements, we investigate the distribution of valence and gap states in copper phthalocyanine (CuPc) upon the introduction of minute amounts of the p-dopant molybdenum tris[1,2-bis-(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd)3). We observe the progressive filling (and deactivation) of the deepest tail states accompanied by a decrease of the hopping transport activation energy by charges introduced by the dopants, as well as a significant broadening of the CuPc density of states. Simulations relate this broadening to the electrostatic and structural disorder induced by the dopant in the CuPc matrix. </p><p> Another challenge in this field is n-type doping. Although a variety of stable molecular p-dopants have been developed and successfully deployed in devices, air-stable molecular n-dopants suitable for materials with low electron affinity, which are exceedingly important in a range of applications, are essentially non-existent. We demonstrate a major advance to n-dope very low electron affinity organic semiconductors using cleavable air-stable dimeric dopants. Although the reduction potentials of these host materials are beyond the thermodynamic reach of the dimer's effective reducing strength, photo-activation of the doped system can result in kinetically stable and efficient n-doping. High-efficiency organic light-emitting diodes are fabricated by using electron-transport layers doped in this manner. Our strategy thus enables a new paradigm for using air-stable molecular dopants to improve conductivity in organic semiconductors with very low electron affinity and provide ohmic contacts to these materials regardless of the electrode work function, giving more freedom to device design and optimization.</p><p>

Transparent p-type CuCr1-xMgxO2 wide band gap oxide semiconductor thin films were deposited over quartz substrates by chemical spray pyrolysis technique using metalloorganic precursors. A mechanism of synthesis of CuCrO2 films involving precursor decomposition, oxidation, and reaction between constituent oxides in the spray deposition process is presented. Crystalline single phase CuCrO2 delafossite structure was dominant in ≥700ºC argon ambient annealed films but the as-deposited films contained spinel CuCr2O4 mixed phases as shown by XRD and XPS studies. Spin-orbital energy ∼9.8eV in Cr 2p electron spectra consistent with Cr3+ valence state and Cr 2p3/2 resolved peaks show mixed valence state on Cr4+ /Cr6+ confirming CuCr1-xMgxO 2 compound phase in the films. Effect of substrate temperature, film thickness, and acceptor Mg2+ doping on crystallographic structure, optical, electrical conductivity and thermoelectric coefficient was investigated. The invariance of the α- and increase of the c-lattice parameter with Mg concentration suggests that Mg2+ ions are introduced at the Cr3+ site. Highly transparent ≥80% CuCr 0.93Mg0.07O2 films with direct and indirect optical band gaps 3.08 and 2.58eV for 155 nm and 3.14 and 2.79eV for 305nm thin films, respectively were obtained. Photoluminescence emission bands at 532 and 484nm interpreted to arise from 3d94s1 and 3d 10 Cu+ intra-band transitions. Electrical conductivity of CuCr0.93Mg0.07O 2 films ranged from 0.6−1.0 Scm-1 and exhibits activation energies ∼0.11eV in 300-420K and ∼0.23eV in ≥ 420K region ascribed to activated conduction and grain boundary trap assisted conduction, respectively. Restricted by the Mg solubility, the substituted Mg dopants limited to x≤0.05 are only able to contribute to the optimum hole carrier in the range ∼2−4×1019cm-3 and thus no substantial increase of electrical conductivity could be realized with increased Mg concentration. A major fraction of Mg atoms do not act as acceptor, but beyond the low solubility limit act as defect centers. Transparent p-CuCrO2/n-ZnO heterojunction diodes showing rectifying current-voltage characteristics were fabricated. The forward to reverse bias current ratio was estimated as ∼128 and ∼108 at ±1V and ±2V, respectively. Built-in voltages of p-CuCrO2/n-ZnO heterojunctions discerned from small signal capacitance measurement are 1.27 and 0.67V, attributed to the alignment of Fermi level and distribution of interface trap states, respectively.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7602. Adviser: John A. Rogers. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.