Built-In Potential in Conjugated Polymer Diodes with Changing Anode Work Function: Interfacial States and Deviation from the Schottky-Mott Limit.
We use electroabsorption spectroscopy to measure the change in built-in potential (VBI) across the polymer photoactive layer in diodes where indium tin oxide electrodes are systematically modified using dipolar phosphonic acid self-assembled monolayers (SAMs) with various dipole moments. We find that VBI scales linearly with the work function (Φ) of the SAM-modified electrode over a wide range when using a solution-coated poly(p-phenylenevinylene) derivative as the active layer. However, we measure an interfacial parameter of S = eΔVBI/ΔΦ < 1, suggesting that these ITO/SAM/polymer interfaces deviate from the Schottky-Mott limit, in contrast to what has previously been reported for a number of ambient-processed organic-on-electrode systems. Our results suggest that the energetics at these ITO/SAM/polymer interfaces behave more like metal/organic interfaces previously studied in UHV despite being processed from solution.
†Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
Bradley A
BA
MacLeod
†Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
Noah E
NE
Horwitz
‡Department of Chemistry, University of Arizona, Tucson, Arizona 85721, United States.
Erin L
EL
Ratcliff
‡Department of Chemistry, University of Arizona, Tucson, Arizona 85721, United States.
Judith L
JL
Jenkins
‡Department of Chemistry, University of Arizona, Tucson, Arizona 85721, United States.
Neal R
NR
Armstrong
§School of Chemistry and Biochemistry, and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
Anthony J
AJ
Giordano
§School of Chemistry and Biochemistry, and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
Peter J
PJ
Hotchkiss
§School of Chemistry and Biochemistry, and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
Seth R
SR
Marder
†Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
Charles T
CT
Campbell
†Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
David S
DS
Ginger
OPV; Super Yellow; built-in potential; interface; organic photovoltaics; oxide; phosphonic acids; self-assembled monolayers