+ (1 - The Hong Kong Polytechnic University

polyu.edu.hk

+ (1 - The Hong Kong Polytechnic University

There are also interesting structural confinement effects

e.g. glass transition temperature not the same as in bulk

Relevance of the Nano-scale?

• Not just a matter of working with nanometric sized objects.

• Nanometer dimensions provide the natural length scale on which many

properties can be tuned:

• Kuhn segment lengths for conjugated polymers: ~ 10 - 30 nm

• Exciton diffusion lengths: ~ 5 - 50 nm

• Förster transfer radii: ~ 1 - 10 nm

• 1/e absorption depths: ~ 20 - 200 nm

• Together with limitations on carrier transport (hopping between nm

domains) this leads to typical device layer thicknesses ~ 10 - 100

nm

• This in turn leads to important optical confinement and interference

effects in near UV through visible to near IR spectral range of interest

(nd ≈ λ) e.g. cavity resonances in diodes, etc

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