Soft Templating of Water Aggregates Disrupts π–π Stacking in Crystalline Poly(3-hexylthiophene)

Abstract

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 A 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 beha...