Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2012_2013/SILVA%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 25th October 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Carlos Silva
Département de Physique & Regroupement québécois sur les matériaux de pointe
Université de Montréal
“The dependence of charge recombination dynamics on the solid-state microstructure in neat, semicrystalline polymeric semiconductors”
ABSTRACT
We investigate the dynamics of geminate-polaron-pair recombination in the neat polymeric semiconductor regioregular poly(3-hexylthiophene) (P3HT) by means of time-resolved photoluminescence (PL) spectroscopy as a function of the solid-state microstructure, imposed by the molecular weight of the polymer and the thin-film processing route. At 10K, we observe delayed PL that originates from recombination of long-lived geminate-polaron pairs. The delayed PL decays over microsecond timescales, which is orders of magnitude longer than the exciton lifetime. We find that >36% of the total PL in solution-processed films of high-molecular-weight (331 kg/mol) material, which features a two-phase semicrystalline microstructure of alternating chain-entangled amorphous phases and crystalline lamella. In this microstructure, both the yield and the decay dynamics depend upon molecular weight. However, in films with dominant one-phase chain-extended microstructures, delayed PL is strongly suppressed. We thus find that a two-phase morphology leads to a higher yield of delayed PL with a higher distribution of decay rates than one-phase, chain-extended morphologies. By invoking a kinetic model including interconversion of excitons and geminate polarons, we conclude that geminate electron-hole pairs are on average further apart in two-phase morphologies, and that these microstructures result in a higher yield of geminate pairs that do not recombine within the timeframe of our experiment.
Refreshments will be available.