Molecular Orientation-Dependent Interfacial Energetics and Built-in Voltage Tuned by a Template Graphene Monolayer

TitleMolecular Orientation-Dependent Interfacial Energetics and Built-in Voltage Tuned by a Template Graphene Monolayer
Publication TypeJournal Article
Year of Publication2015
AuthorsZhang, LS, Roy, SS, Hamers, RJ, Arnold, MS, Andrew, TL
JournalJournal of Physical Chemistry C
Volume119
Issue1
Pagination45-54
Date PublishedJan
ISBN Number1932-7447
Keywordscharge-transfer states, energy-level alignment, gap states, identification, interfaces, organic heterojunction, pentacene thin-films, probe force microscopy, semiconductors, solar-cells, surfaces
Abstract

Highly transparent and conductive monolayer graphene was used as a template to tune the crystal orientation of pentacene from generic standing-up (001) to lying-down (022) in neat films. Spatially resolved Kelvin probe force microscopy (KPFM) was used to reveal the energy levels of pentacene thin films grown on substrates with and without the template graphene layer, as well as the energy level alignment in various pentacene-containing organicorganic heterojunctions. A correlation between crystal domain orientation and the work function was directly observed using KPFM. Up to 0.36 eV shifts in work function were observed in neat pentacene films over large areas (>0.5 in.(2)) upon orientation transition, likely due to the transition from Fermi level pinning (standing-up pentacene on ITO) to vacuum level alignment (lying-down pentacene on grapheneITO). Morphology-induced energy level shifts versus interfacial electronic equilibration effects were disentangled using atomic force microscopy, KPFM, X-ray diffraction, and Raman data for neat pentacene films and pentacene containing heterojunctions on monolayer graphene. The data detailed herein provide a fundamental picture of the major interfacial effects active in optoelectronic devices containing a bare graphene electrode.

URL<Go to ISI>://WOS:000347744700007