Effect of graphene substrate on the spectroscopic properties of photovoltaic molecules: role of the in-plane and out-of-plane pi-bonds

TL;DR

This study investigates how graphene substrates influence the electronic and optical properties of pentacene molecules, revealing charge redistribution, weak pi-bond formation, and spectrum modifications due to molecular distortions and substrate interactions.

Contribution

It provides new insights into the effects of graphene on photovoltaic molecules' spectroscopic properties, including charge transfer and optical spectrum changes, using density functional theory.

Findings

Molecular distortions significantly alter isolated pentacene's absorption spectrum.

Adsorbed pentacene's optical spectrum closely resembles that of graphene.

Chemical modifications at terminal groups affect energy levels and interactions.

Abstract

The electronic structure of pentacene decorated with dipole groups (d-pentacene) and adsorbed onto a graphene substrate has been studied within the density functional theory. Three reference configurations have been considered, namely the ideal molecule without distortions, the actual molecule including intramolecular distortions and the molecule adsorbed onto graphene. Calculations show a noticeable charge redistribution within the d-pentacene + graphene system due to molecular distortion, as well as the formation of weak $\pi$-bonds between the molecule and the substrate. Additionally, the effect of the chemical modification of the terminal saturation with --H by --OH and =O is checked to explore the possibility of "levels engineering". The imaginary part of the dielectric function of d-pentacene in the ideal and distorted conformations and the molecule adsorbed at graphene were calculated within the random phase approximation. Results show that, even though molecular distortions change apreciably the absorption spectrum of isolated d-pentacene, the adsorbed molecule exhibits an optical spectrum which mimics quite much that of single graphene.