Investigations on some selected conducting polymers and polymer ...
Investigations on some selected conducting polymers and polymer ...
Investigations on some selected conducting polymers and polymer ...
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I ntroducti<strong>on</strong><br />
less than the width of the device. But the observed values of currents<br />
are found to be reas<strong>on</strong>ably lower than that predicted by theory. Also<br />
Parker model fails to give evidence for the prep<strong>on</strong>dence of triangular<br />
barrier over schottky barrier.<br />
Reiss etal have proposed schottky barrier model for ITO/PPV/AI<br />
device. In this model, currents are assumed to be predominantly due to<br />
holes. Hole currents are limited more by PPV/AI interface than by<br />
ITO/PPV interface. They model the current-voltage characteristics<br />
using the equati<strong>on</strong> for thermi<strong>on</strong>ic emissi<strong>on</strong> across a schottky barrier<br />
from a semic<strong>on</strong>ductor into a metal. Doping levels estimated for these<br />
devices are c<strong>on</strong>siderably higher than those estimated by Marks etal. But<br />
n<strong>on</strong>e of these models is universally accepted. Each has its own merits<br />
<strong>and</strong> demerits.<br />
Heterolayer LEDs<br />
Electr<strong>on</strong> <strong>and</strong> hole flow can be optimized by forming<br />
heterojuncti<strong>on</strong>s between the semic<strong>on</strong>ducting layers.<br />
An example is an ITO/PPV/CN-PPV/Al device. PPY is<br />
processed from a st<strong>and</strong>ard precursor <strong>polymer</strong> <strong>on</strong>to ITO <strong>on</strong> a glass<br />
substrate. Cyano PPV (CN-PPV) is spin cast <strong>on</strong> the top of it. Top<br />
electrodes are coated using thermal evaporati<strong>on</strong>. Basic scheme for<br />
the device is given below.
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