Ab initio calculations of the optical absorption spectra of C60-conjugated polymer hybrids

TL;DR

This study employs linear-scaling density-functional theory to compute the optical absorption spectra of C60-polymer hybrids, revealing charge transfer characteristics and spectral features relevant for photovoltaic applications.

Contribution

It introduces a LS-DFT approach to analyze large C60-polymer systems, identifying spectral peaks and charge transfer mechanisms not previously accessible.

Findings

Additional absorption peaks below the original onset in PPP hybrids

Charge transfer confirmed between polymer and C60

No new peaks observed in PPV hybrids

Abstract

A recently developed linear-scaling density-functional theory (LS-DFT) formalism is used to calculate optical absorption spectra of hybrids of C60 and the conjugated polymers poly(para-phenylene) (PPP) and poly(para-phenylene vinylene) (PPV). The use of a LS formalism allows calculations on large systems with realistic proportions of C60, which has been of interest for the use of such materials in photovoltaics. Two different bonding structures are tested for the hybrid PPP and for both systems additional peaks are present in the absorption spectra below the original onset of absorption. By identifying the eigenstates involved in the relevant transitions, a weighted density difference is formed, demonstrating the transfer of charge between the polymer chain and the C60, in agreement with experiment. For the hybrid PPV, no additional peaks are observed in the absorption spectrum.