P3HT-Fullerene Blends: a Classical Molecular Dynamics Simulation

TL;DR

This study uses classical molecular dynamics simulations to investigate the morphology and phase separation behavior of P3HT-fullerene blends, revealing a tendency for fullerene molecules to segregate regardless of initial distribution.

Contribution

It introduces a specific Nanomol Force Field for simulating polymer/fullerene blends and provides insights into their phase separation behavior at room temperature.

Findings

Fullerene molecules tend to segregate in the blend.

Phase separation dominates regardless of initial distribution.

Simulations involve large systems of ~40,000 atoms.

Abstract

Blends of polymer and C$_{60}$-derived molecules are in the spotlight in recent years for application in organic photovoltaics, forming what is known as bulk-heterojunction active layers. The character of the heterojunction is determinant, with clear relevance of morphology and phase separation. To better understand the morphology of the systems, we present a classical molecular dynamics (CMD) simulation of polymer/fullerene (P3HT/C$_{60}$) blends, coming from different starting points, using the specifically designed Nanomol Force Field based on the Universal Force Field. We use not-so-short regioregular polymers with 30 hexyl-thiophene units ($\sim$5kg$\cdot$mol$^{-1}$ molecular weight) and, adopting a $\sim$ 1:1 mass proportion for the polymer:molecule blend, we simulate cells of $\sim$ 40 thousand atoms, at room temperature and normal pressure conditions. We find that, independently of the starting-point spatial distribution of C$_{60}$ molecules relative to P3HT chains, segregated or isotropic, the fullerene molecules show a tendency to segregate, and phase separation is the dominating regime.