NONRADIATIVE DECAY CHANNELS IN POLY(3-HEXYLTHIOPHENE) AND POLY(3-DODECYLTHIOPHENE) AND HOW TO CONTROL THEM BY MOLECULAR ENGINEERING

We report a photoluminescence study of poly(3-alkylthiophene) films. T he quantum yield of photoluminescence of amorphous films is higher tha n that of semicrystalline films. Temperature dependence measurements r eveal an intrachain non-radiative decay channel (NRDC) with an activat ion energy of 0.015 eV in semicrystalline films. The quantum yield inc reases with increasing alkyl chain length, suggesting that an intercha in NRDC is also responsible for the low quantum yields in these materi als. We find that the confinement parameter gamma of the polaron-excit on increases when the film order increases, indicating that the two su blevels are closer to the band edge in ordered films owing to a strong intermolecular interaction. The value of gamma for poly(3-dodecylthio phene) is lower than that for poly(3-hexylthiophene), indicating a lar ger tight-binding energy in the former.