Influence of disorder on the photoinduced excitations in phenyl substituted polythiophenes

Regioregular poly(3-(4'-(1 " ,4 " ,7 " -trioxaoctyl)phenyl)thiophenes) (PEO PTs) exhibit interesting properties for the use in polymer electronics. Exp osing thin films of the amorphous, disordered phase (orange phase) of the " as prepared" polymer to chloroform vapor or annealing them by heat treatmen t results in a redshift of the absorption maximum due to the formation of n anocrystals in an ordered phase (blue phase). As such, PEOPT thus is a very interesting conjugated polymeric material, which exhibits two different ph ases with well-defined order/disorder characters on one-and-the-same materi al. This property opens up the unique possibility to investigate the role o f order/disorder on the photoexcited pattern without being obscured by the differences in chemical structure by using different materials with differe nt crystallinity. The fact, that blue phase PEOPT exhibits absorption edges at relatively low energies around 1.8 eV, thereby demonstrating an enhance d spectral absorption range as compared to the orange phase, makes them att ractive for use in photodiodes and solar cells as well. The photoinduced ch arge generation efficiency in both phases of PEOPT is significantly enhance d by the addition of a strong electron acceptor such as fullerene C-60, as observed by quenching of the luminescence and by photoinduced absorption me asurements in the infrared and uv-visible regime. The average number and th e lifetime of photoinduced carriers in composites of PEOPT with a methanofu llerene [6,6]-phenyl C-61-butyric acid methyl ester (PCBM) are found to dep end on the crystallinity of PEOPT in thin films, which gives rise to charge d photoexcitations delocalized between polymer chains. Stronger bimolecular recombination in composites of the blue phase PEOPT with PCBM is observed as compared to the orange phase PEOPT/PCBM films. The origin of this enhanc ed recombination is found to be related to the hole mobility of the polymer . (C) 2001 American Institute of Physics.