Notes
Outline
Polymer electronics
Polymer Electronics
(A tutorial)
General electrical properties
Conducting polymers behave as semiconductors
Applications:
FET transistors (no doping)
Conventional Semiconductors: The top down approach
Conventional Semiconductors at the atomic level
When charge is moving the key word is mobility, mobility, mobility (cm
2
V
–1
s
-1
)
p-conjugated “polymers” (pentacene) at the molecular level
Consequences of molecular morphology in poly(3-alkylthiophenes)
The bigger picture
Major applications:
LEDs
Evolution of LED/OLED performance
A litany of new materials
A simple picture of photophysics
in isolated molecules
A simple picture of intrachain photophysics for a conjugated polymer
Engineering where the energy goes in and where it comes out
Keys to conducting polymer applications:
Synthetic control and processibility
Addition of solubilizing side chains to “conducting” polymers has created a myriad of new, processible polymers.
Self-Assembly (or … you I like, but you I hate)
For example: Self-assembly leads to ordered (lamellar) phases
Side chain behavior couples to main chain conformation: Thermochromism, solvatochromism, ionochromism,…
“Self-assembly” leads to formation of helical phases
Side chain ordering does not always work in your favor!
Morphology impacts energy flow in subtle ways:
In the case of a bimodel distribution of conformations
Model depicting energy transfer from disordered to ordered phase
Back to electronic properties….
p-conjugated polymers have unusual charge excitations
Minding the gap
Schematic representations of recombination pathways
Recombination is spin dependant
There is more to the singlet-triplet story
Electronic band structure in one-dimension: A primer
Tight-binding for p-electrons and semiconducting polymers
Extending the chain
A one-dimensional chain (trans-polyacetylene)
After a simple approximation: [B(0) is approx. 1]
The Peierls instability (1939)
Conformational structure impacts electronic properties
Simple picture of polyacenes and poly-p-phenylenes
Now from the tight binding perspective
Poly-p-phenylene from tight binding
Impact of band structure on photocell device physics
A closer look at the calculation
Separating electrons and holes:
A prerequisite for photovoltaic applications
Blended device behavior
The future
(assuming one has a good crystal ball)
Notes