Enhanced Reciprocal Interactions between Molecular Stresses and Optoelectronic Energy Transfers for High Efficiency Long Life Devices Based on Conjugated Polymers
Final rept. 11 Apr 2013-10 Apr 2014
NATIONAL TSING HUA UNIV HSINCHU (TAIWAN)
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This report describes an investigation into the effects of mechanical deformation on photoluminescence PL behavior for the neat conjugated polymers poly2-methoxy-5-2-ethylhexyloxy-1,4-phenylenevinylene MEH-PPV and polythiophenes P3HT, P3BT, P3EHT. This study used a unique bilayer stretching method where the thin conjugated polymer was drawn into local deformation zones at very high local mechanical strain 300 on top of glassy polystyrene film. It was found that very large PL enhancement i.e., as high as 60x was observed for neat MEH-PPV polymers during mechanical deformation, which was comparable to that observed in the dilute systems. In contrast, for crystalline neat P3HT films, bilayer stretching resulted in insignificant PL enhancement. Substantial PL enhancement emerged 15x, however, when strong intermolecular interactions were obstructed by bulky side-groups in P3EHT. The results indicated that once conjugated polymer chains are effectively stretched and thus confined by mechanical stresses, suppression of electron-phonon coupling can prevail in the neat resins to give rise to the dramatic efficiency enhancements. Such enhancement was not found to be exploited via imprinting methods unless proper precautions were taken during mechanical strain. The reciprocal relation that mechanical behavior of conjugated polymer chains can be controlled by light absorption was also explored. By shining light through an optical mask, the movements of conjugated polymers in a thin film can be manipulated to form patterns in accordance to that on the mask. Electro-poling also produced molecular stress effects on efficiency enhancement in conjugated polymers.
- Polymer Chemistry