Internal photoemission in molecular junctions: Parameters for interfacial barrier determinations

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Journal titleJournal of the American Chemical Society
Pages12961304; # of pages: 9
SubjectMolecular orbitals; Photocurrents; Self assembly; Energy level alignment; Experimental parameters; Interfacial barriers; Interfacial energetics; Internal photoemission; Molecular components; Photocurrent spectrum; Secondary mechanisms; Photoemission; molecular layer; chemical structure; electrochemical analysis; electron transport; illumination; internal photoemission; light absorption; light intensity; molecular electronics; orbit; photon; steady state
AbstractThe photocurrent spectra for large-area molecular junctions are reported, where partially transparent copper top contacts permit illumination by UV-vis light. The effect of variation of the molecular structure and thickness are discussed. Internal photoemission (IPE), a process involving optical excitation of hot carriers in the contacts followed by transport across internal system barriers, is dominant when the molecular component does not absorb light. The IPE spectrum contains information regarding energy level alignment within a complete, working molecular junction, with the photocurrent sign indicating transport through either the occupied or unoccupied molecular orbitals. At photon energies where the molecular layer absorbs, a secondary phenomenon is operative in addition to IPE. In order to distinguish IPE from this secondary mechanism, we show the effect of the source intensity as well as the thickness of the molecular layer on the observed photocurrent. Our results clearly show that the IPE mechanism can be differentiated from the secondary mechanism by the effects of variation of experimental parameters. We conclude that IPE can provide valuable information regarding interfacial energetics in intact, working molecular junctions, including clear discrimination of charge transport mediated by electrons through unoccupied system orbitals from that mediated by hole transport through occupied system orbitals.
Publication date
PublisherACS Publications
AffiliationNational Research Council Canada (NRC-CNRC); National Institute for Nanotechnology
Peer reviewedYes
NPARC number21275786
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Record identifier9823fcfa-3db2-4f50-af4e-8777b56a75bc
Record created2015-07-14
Record modified2016-05-09
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