This document describes the fabrication of a thin film polymer light-emitting diode (OLED). It involves coating an indium tin oxide (ITO) substrate with the light-emitting polymer MEH-PPV dissolved in chloroform, followed by a layer of PEDOT:PSS as a hole transport layer. When a voltage is applied, electrons and holes recombine in the MEH-PPV layer, causing it to emit a bright orange glow. The project allows students to develop an understanding of OLED technologies and their applications. Challenges included finding solvents that could dissolve the polymer and using an appropriate molecular weight of MEH-PPV. Future work may involve testing other electrolumines

1. Fabrication of Thin Film Polymer Light-Emitting Diode
Steven 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:PEDOT
Organic 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 Alcohol
Windex
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
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Materials on OLEDs with Semiconducting Polymers." Education Quimica 24.1 (2012): 17-22.
Print.
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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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