Molecular Dynamics Simulations of Organic Photovoltaic Materials: Structure and Dynamics of Oligothiophene
SY Reddy and VK Kuppa, JOURNAL OF PHYSICAL CHEMISTRY C, 116, 14873-14882 (2012).
Molecular dynamics simulations using atomistically detailed force fields are reported to investigate the behavior of prototypical conjugated polymers in the presence of a fullerene substrate. Four-membered oligothiophene (4TH) molecules are studied adjacent to a C-60 phase in an architecture that is typical of the present generation of organic photovoltaic devices. The simulations focus on the structure, orientation, and conformations that develop in the 4TH phase adjacent to the surface and are compared with bulk systems. Effective conjugation lengths in 4TH chains are shifted to significantly lower values as compared with the bulk. Chain backbone torsional transitions between trans and gauche states are counterintuitively accelerated next to fullerene and are found to be strongly correlated with density fluctuations in the polymer phase. The results demonstrate the role of the substrate in controlling nanoscale morphology of the active material in solar cells and reveal qualitative changes in the temperature- dependent behavior of 4TH in the bulk and in the presence of fullerene.
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