Monte Carlo study of picosecond exciton relaxation and dissociation in poly(phenylenevinylene)

Conformational disorder and energy migration in MEH-PPV with partially broken conjugation

“…17,[21][22][23][24][25][26][27] The Förster transfer rate is calculated by summing the dipole-dipole interactions between each individual pair of monomers on different spectroscopic units. The orientation and position of the single monomer within a spectroscopic unit is thus needed, even though the excitation is assumed to be delocalized over a spectroscopic unit.…”

Ultrafast depolarization of the fluorescence in a conjugated polymer

“…5 Soluble polymers, particularly poly͓2-͑2'-ethylhexyloxy͒-5-methoxy-1,4-phenylenevinylene͔ ͑MEH-PPV͒, have received a lot of attention, because solution processing provides easy shaping and simplicity in device manufacturing. The primary optical excitations in these materials are correlated electron-hole pairs-excitons, [6][7][8][9][10][11][12] which show intermediate properties between small radius Frenkel excitons of molecular aggregates and large radius Wannier-Mott excitons in inorganic semiconductors. A very important parameter determining excited state dynamics is exciton delocalization length, which depends on electronic coupling, site energy disorder, and electron-phonon coupling.…”

“…Instantaneous delocalization of the exciton over at least 50 repeat units, which corresponds to 400Å, was estimated from the measured anisotropy of the electroabsorption signal in films of oriented MEH-PPV, 13 which also showed a lower binding energy of the exciton 12 than the disordered films. 8,10 Exciton delocalization in solutions and unoriented spin-coated films of MEH-PPV as well as those of unsubstituted poly͑phenylenevinylene͒ ͑PPV͒ prepared from a precursor was estimated to be between 6 and 17 repeat units from fits to absorption spectra. 14,15 This estimate depends on whether the blueshift and broadening of absorption originates from conjugation-disrupting defects, such as kinks and twists in the backbone 16 or from the "wormlike" conformational disorder, which gradually weakens the conjugation in the absence of abrupt conjugation breaks.…”

Simulating charge transport in organic semiconductors and devices: a review

“…To model the process of charge generation in OPV devices, one must additionally consider the photogeneration, transport, relaxation and dissociation of excitons [145,146]. In keeping with the ethos of KMC modelling, this is usually achieved by considering rate equations which are believed to be appropriate for OPV materials and fitting the model to experimental data [147,148], although quantum chemical calculations can be integrated to examine exciton transport in more detail [146].…”

“…Photogenerated excitons are created at random sites within the simulation volume at a rate which is proportional to the incident light intensity and absorption length of the materials in question. Photogenerated excitons then hop with a modified Miller-Abrahams rate [145] :…”