Organic Light Emitting Diodes (OLED) July 2011

Organic Light Emitting Diodes Solid State Semiconductor 100 to 500 nanometers thick Emits light when electricity is applied Suitable for small displays, TVs, and thin area (panel) lighting

How OLEDs Work Electrical current is applied and electrons travel from the cathode to the emissive layer to the conductive layer to the anode The removed electrons leave “holes” and the traveling electrons find them Once the vacancy is filled the electron falls into an energy level of the atom that has the “hole” By falling into the energy level the electron gives up energy in the form of a photon This process releases visible light

Changing Parameters Intensity (Brightness): Dependent on Current, more current equals brighter light. Not dependent on voltage Color Saturation, Lifetime, and Efficiency: Dependent on the number of layers, typically ranging from 2 to 5 Efficiency: Doping with organometallic materials improves efficiency

OLED Schematic Cathode injects electrons, emissive layers gives off photon anode removes electron when electrical current is supplied

Example of OLED Cell Material

Commonly Used Polymers Polymers used in PLED's must be: Electrically conductive Highly photoluminescence efficient Conjugated polymers are good energy producers due to the energy gap between pi bonding states Polycarbazole and PFO (poly (9,9-dialkyfluorene) are commonly used PEDOT:PSS is a good hole transporting polymer, but more research needs to be done to find a better one

Different Types of OLEDs Molecular Categories Small Molecule (SMOLED) Weigh less than 1000g/mol Used in evaporation deposition methods Much more advanced- Used in all OLED products More efficient than PLED due to deposition techniques Polymer (PLED) Large molecule OLED Weigh more than 1000 g/mol Able to be put into a solution Used in spin coating and inkjet printing deposition methods More research is needed but they are capable of being used in more flexible, lower voltage applications, which makes them candidates for larger displays

Most Popular Designs Top Emitting OLED Bottom Emitting OLED Transparent Cathode / Reflective Anode Most Efficient Larger aperture ratio results in higher resolution Bottom Emitting OLED Reflective Cathode / Transparent Anode Light reflected through glass substrate Transparent OLED Both Cathode and Anode are transparent Light emitted in both directions

Diagrams of Transparent and Top Emitting OLED's

Different Formations AMOLED Active Matrix OLED Made by layering different layers of the cell Has a thin film transistor which the anode overlays The thin film transistor determines which pixels get turned on and off to form an image Pro: Uses less power than passive matrix OLED Most commonly used in larger displays Computer Monitors, Flat-Screen TV's, Electronic Billboards

Different Formations PMOLED Passive Matrix OLED Constructed of strips of the different layers Anode strips arranged perpendicular to cathode strips Intersection of cathode and anode make pixels, which is where light is emitted External power source used to determine which pixels get turned on and off Pro: Easy to make Con: Consumer more power Used most commonly is small screens (3in diagonal)

Diagram of Passive and Active Matrix OLED's

Stacked OLEDs Red, Green and Blue layers stacked on top of each other, opposed to side by side Creates smaller pixel size Higher resolution All three colors together make white light All connected together requires color filter Less efficient because 50% of light lost in filter

True Stacked OLEDs Still stacked on one another Each color is connected separately to the electrical source Allows for no color filter to be needed More efficient Used in larger pixel devices

Other Types of OLEDS Foldable OLED White OLED Made of very flexible foils or plastics Lightweight and durable Used in cell phones and PDA's to reduce breakage Future uses include integration into fabrics to make clothes that have a cell phone, GPS and computer chip integrated into them White OLED Emits white light that is brighter than fluorescent bulbs Have the benefit of true color qualities like incandescent bulbs Can be manufactured into large sheets for home and business uses Have the ability to reduce energy costs

Manufacturing OLEDs

Backplane Switching and driving circuitry OLEDs require thin film transistor (TFT) Must be strong and stable, more so than in a LCD TFT Common TFT Material Amorphous Silicon Low Temperature Polysilicon (LTPS) (AMOLED) Oxide TFT, Super Grain Silicon, InGaZnOx

Depositing and Patterning Vacuum Evaporation (VTE) Deposition method used to manufacture all OLEDs on the market today Molecules are heated, evaporated and then condensed on a cool substrate Shadow mask used to make pixels Very expensive and inefficient Difficult to scale to production level Difficult to scale up because the metal mask is very delicate and with size it becomes susceptible to bending and breaking

Depositing and Patterning Organic Vapor Phase Deposition (OVPD) Uses low pressure and high temperatures In a chamber, a carrier gas moves evaporated material to cooled substrate Not used in mass production More efficient and precise than VTE

Depositing and Patterning Laser Annealing Laser used to pattern organic material First film is made by VTE, then the film is placed on a substrate Laser used to heat material and transfer film to substrate Laser Induced Thermal Imaging Much more accurate than VTE Achieves higher pixel density and easier to scale

Depositing and Patterning Inkjet Printing Inkjet used to spray solution processable OLED material onto substrate Fast, efficient and scalable compared to other methods Disadvantage: Creating a reliable and efficient solution processable OLED Commonly used with PLEDs but can be used with SMOLED Solution processable OLED material does not have as long of a life span as OLED material that can be evaporated and applied onto a substrate.

Other Deposition Techniques Dupont Developed spray printing process Uses nozzles for continuous spray Nozzles move at 4-5 m/sec Less efficient display than other techniques but could result in a cheaper display than an LCD Can print a 50” OLED TV in less than 2 minutes Other Methods Roll to Roll Spin Coating

Encapsulation OLEDs are very sensitive to moisture and oxygen Must be protected by shield or barrier Barrier must be cheap, flexible, and not labor intensive Permanently bonded with epoxy or resin Must be chemically, water, heat and solvent resistant Classic barrier used is glass, but is bulky and heavy Metal is a good barrier, but it is not transparent New materials being used include plastics and nanomaterials

Advantages of OLEDs Power Consumption: No backlighting required, more efficient than LCD Lighting: More aesthetic properties than other forms of light, does not require shades Environment: Do not contain any heavy, toxic metals Materials: Very simple structure compared to LCD Transportation: Very light, less gas needed and pollution due to transporting materials Lifetime: Potential to have long life, not attainable right now Size: Much thinner than other technologies and much brighter View: Large field of view (170 degrees)

Disadvantages of OLEDs Lifetime: Currently very undependable Blue lifetime much shorter than other materials Solution: Use red and green phosphorescent materials and blue fluorescent material (Short Term Fix) Scaling: Not easy to go to production due to issues with the backplane and deposition/patterning phases Lighting: Inorganic OLEDs will always be more efficient Direct Sunlight: Can not see OLED in sunlight Production: Very wasteful, overspray and energy efficiency

Displays Currently range from 0.66” to 5.5” on regular market Super expensive commercial displays up to 17” Set backs: Blue fluorescent lifetime, scaling to production, and deposition techniques Future: Economically feasible, more efficient displays, larger in size

Lighting Currently only in small quantities and on the luxury market Not as efficient as LCDs, but more aesthetically pleasing Lamp sells for 25,000€ Future: Hope to get cheaper and be mass produced Need to work on efficiency

OLED Market 4 major areas Chemicals/Materials Deposition Encapsulation Manufacturing Equipment Total Market in 2009 was estimated to be $ 1billion Total Sales of AMOLED and PMOLED $800million

Top Companies Samsung $566 Million in Revenue RiTDisplay $106 Million in Revenue Pioneer $60 Million TDK $42 Million Visionox $15 Million Others: Sony, Philips, Fraunhofer, Lumiotec, OSRAM, Vitex, SNU Precision, AUO

Market: Past, Present, Future 2009: PMOLED Sales $300 Million, AMOLED Sales $500 Million OLED: Currently $1 Billion market 2015: $1.4 Billion OLED Materials 2015: $1.8 Billion OLED TVs 2015: $500 Million Transparent Conductors 2018: $6 Billion Lighting Substrate and Encapsulation 20% of total cost

Where Does Sono-Tek Fit In? Spray solution processable OLED material Reduce waste and overspray Increase process efficiency Films have very high uniformity increasing their efficiency and durability Lower consumer cost, more economically feasible Lower capital cost compared to other deposition techniques ExactaCoat: R&D and Small Batch Processes FlexiCoat: R&D and small scale production

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