Fabrication of Thin Film Polymer Light-Emitting DiodeSteven Johanning and Soma Chattopadhyay

Department of Chemistry, University of Wisconsin-Platteville, 1 University Plaza, Platteville, WI, 53818

Future Directions

Preparation of ITO Slides for Polymer Deposition

References

Abstract MEH:PPV – light emitting polymer

Poly(phenylene vinylene) (PPV) serves as the electron-transfer layer in light-emitting diodes. PPV, however very stable, is insoluble in most solvents. MEH:PPV helps the solubility of PPV by adding additional alkyl groups to the phenylene rings, making the material more soluble in common solvents, like chloroform and xylene.

PSS:PEDOTOrganic light-emitting devices continue to gather a great deal of attention because of potential applications in flat panel displays and mobile devices which have become ubiquitous. These devices have been studied extensively because of the low cost of the materials involved and the ease of the manufacturing processes. These devices emit light when an electric current is passed through the polymer coated onto a conducting substrate like Indium tin oxide (ITO). The goal of this project is the fabrication of a light-emitting devices by coating a transparent indium tin oxide (ITO) substrate with poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) dissolved in chloroform which serves as the emissive layer. When an electric bias is applied, a bright orange glow is observed. The project allows us to develop an understanding of the underlying physical principles and device technologies of OLEDs and their applications in the real world.

Schematic diagram for the general fabrication protocol

Device Testing

• After successive layers of polymer are spin-coated onto the slide, the masking tape is removed to expose ITO.

• Electrical connections are made through the ITO and the eutectic.

• When the voltage is turned on, a bright orange glow appears.

Solvents Boiling Point(°C) Dissolved the Polymer

Xylene 139 No

Toluene 111 No

Chloroform 61 Yes

Challenges encountered in developing the protocol

• Xylene and Toluene did not dissolve the polymer easily but chloroform did. However, chloroform evaporates quickly, altering the concentration of the polymer solution.

• Device fabrication with a low molecular weight MEH:PPV (40,000-70,000) was not successful and more work is needed. Changing to a larger molecular weight MEH:PPV (150,000-250,000) led to a successful device fabrication.

Future research in studying the current-voltage characteristics of other electroluminescent polymers to find their threshold voltages and test to see if they could be a good fit for the fabrication of light emitting devices. 

PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)) is a highly conductive and transparent polymer. It server as a hole transport layer (HTL) between the anode and the light-emitting layer (MEH:PPV). In addition, PEDOT:PSS works by smoothing out the ITO surface to eliminate any short-circuits that would cause the device to fail.

Indium Tin Oxide (ITO) Slide

Ammonia-Based DI Water Isopropyl AlcoholWindex

Unpolished flat glass slides coated on one side with Indium Tin Oxide (ITO) were obtained from Delta Technologies Limited (Rs 9 -15 ). The ITO slides were cleaned by successive immersion in ammonia based solution, distilled water and Isopropyl alcohol using an ultrasonic bath.

Clean ITO slide Coated with layer Coated with of PSS:DEDOT layer of MEH:PPV

Gallium-Indium eutectic alloy

Power supply attached to slide

Bright orange glow appears when electrical bias is applied

1. Banerji, Amitabh, Michael W. Tausch, and Ullrich Scherf. "Classroom Experiments and Teaching Materials on OLEDs with Semiconducting Polymers." Education Quimica 24.1 (2012): 17-22. Print.

2. Vazquez-Cordova, S., G. J. Ramos-Ortiz, L. M. Maldonado, A. Meneses-Nava, and O. Barbosa-Garcia. "Simple Assembling of Organic Light-emitting Diodes for Teaching Purposes in Undergraduate Labs." Mexican Journal of Physics 54.2 (2008): 146-52. Print.

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