Abstract
In order to have a better knowledge of the impact of mechanical stress and deformation on optoelectronic behavior of conjugated polymers, “two-layer structure stretching” is used in this thesis. In “two-layer structure stretching”, glassy state polymer is used as a substrate which can undergo local necking deformation. The substrate is then topped with polymers we are interested in. Not until these two layers are firmly attached to each other are we going to stretch this structure. With some adequate thickness ratios, top layer is greatly stretched due to the deformation of bottom layer. In our experiments, polystyrene and polycarbonate were used as a substrate. We top the substrate with (1) different ratio of MEH-PPV to PS (2) polythiophenes with different side chains. 89 times of PL enhancement was recorded as stress goes up to 220MPa for 1%MEH-PPV /99% PS case. P3EHT has the weakest intermolecular interaction among P3EHT, P3HT, and P3BT, thus it has the highest PL enhancement. It is the suppression of electron-phonon interaction of molecular segments that leads to the huge PL enhancements. A significant difference between MEH-PPV and polythiophene series is found under the confocal PL. We observe PL peak shifts in film and craze region for MEH-PPV cases, whereas we see no PL peak shifts for polythiophene series. We then use time-resolved up-conversion technique in probing different region of MEH-PPV/PS films, so that we can rebuild the time-resolved PL spectrum on a picosecond timescale. From the time-resolved spectrum, we observe a decrement of the rate of red-shift no matter in 100% MEH-PPV or 70% MEH-PPV/30% PS. We found at least two energy decay mechanism from the fitting curve of delay time versus intensity. The shorter decay time constants increase dramatically in highly stretched region comparing to longer ones. These two phenomenon are both the evidence of the suppression of charge trapping and non-radiative relaxation.