The π–π
stacking robustness of the photoactive
layer is key to maintaining efficiency of organic photovoltaics (OPVs).
We show local disruption more than 2 Å on average in the π–π
stack of crystalline poly(3-hexylthiophene) (P3HT), one of the most
common materials used in OPVs, through formation of a chainlike water
structure with limited growth and mostly pentameric cluster ends.
In contrast, a 3D aggregated water cluster with constant growth is
observed in amorphous P3HT. Dynamics of water molecules that form
the largest aggregates in crystalline P3HT show the effect of limited
mobility, when compared to amorphous P3HT, due to dual confinement
from both alkyl side groups and thiophene backbone. We term this dual
confinement soft templating and quantify its effect
on nature, size, and hydrogen bond participation of water aggregates
in crystalline and amorphous P3HT using all-atom molecular dynamics
with in-house developed potentials that were previously shown to represent
the interfacial and wetting behavior of P3HT systems in good agreement
with experiments. Examination of disruption behavior presented for
P3HT would allow smart molecular design of photoactive layers.