Summer 2012 Intern Project- Kerim Tshimanga

SURFACE MODIFICATION FOR STUDYING TRAP-LIMITED ELECTRON TRANSPORT IN ORGANIC ELECTRONIC MATERIALS


Kerim Tshimanga
Physics
UC Santa Barbara

Mentor: Sam Collins
Faculty Advisor: Quyen Nguyen
Department: Chemistry and Biochemistry

In today growing energy crisis, renewable energy research has garnered significant interest in the scientific community. To that end, our lab has been studying optoelectronic devices, photovoltaic, light-emitting, etc. that employ polymers and organic small molecules instead of inorganic materials like silicon and gallium arsenide. These organic molecules and polymers offer many attractive properties like being solution-processable, high absorption coefficients, and tunability of their structures/properties. Unfortunately, though organics electronics bear these traits, they still don’t yet perform as well as inorganic devices. One of the issues responsible for this is relatively poor charge transport. In our devices some of our electrons don’t make it to collection at the electrodes because they run into obstacles coined as “trap states”. Studying this trap-limited electron transport requires the ability to construct a diode that will only allow electron current to flow. This can be done by choosing an electrode workfunction that lies in between the highest-occupied and lowest-unoccupied molecular orbitals of your materials and one with a workfunction shallower than both. This creates a barrier to hole injection while rectifying electron transport across the lowest-unoccupied molecular orbitals of the materials. In my study, I use surface modification of metals using self-assembled monolayers to shift the workfunctions of inert metals, such as gold or silver, to usable values. These devices then can be used to study the trap-limited charge transport.

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