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Title: Negative polarity of phenyl-C{sub 61} butyric acid methyl ester adjacent to donor macromolecule domains

Interfacial fields within organic photovoltaics influence the movement of free charge carriers, including exciton dissociation and recombination. Open circuit voltage (V{sub oc}) can also be dependent on the interfacial fields, in the event that they modulate the energy gap between donor HOMO and acceptor LUMO. A rise in the vacuum level of the acceptor will increase the gap and the V{sub oc}, which can be beneficial for device efficiency. Here, we measure the interfacial potential differences at donor-acceptor junctions using Scanning Kelvin Probe Microscopy, and quantify how much of the potential difference originates from physical contact between the donor and acceptor. We see a statistically significant and pervasive negative polarity on the phenyl-C{sub 61} butyric acid methyl ester (PCBM) side of PCBM/donor junctions, which should also be present at the complex interfaces in bulk heterojunctions. This potential difference may originate from molecular dipoles, interfacial interactions with donor materials, and/or equilibrium charge transfer due to the higher work function and electron affinity of PCBM. We show that the contact between PCBM and poly(3-hexylthiophene) doubles the interfacial potential difference, a statistically significant difference. Control experiments determined that this potential difference was not due to charges trapped in the underlying substrate. The directionmore » of the observed potential difference would lead to increased V{sub oc}, but would also pose a barrier to electrons being injected into the PCBM and make recombination more favorable. Our method may allow unique information to be obtained in new donor-acceptor junctions.« less
Authors:
; ; ;  [1] ;  [2] ; ;  [3] ;  [4]
  1. Department of Materials Science and Engineering, Johns Hopkins University, 206 Maryland Hall, 3400 North Charles Street, Baltimore, Maryland 21218 (United States)
  2. Department of Electrical and Computer Engineering, University of Wisconsin, 415 Engineering Drive, Madison, Wisconsin 53706 (United States)
  3. Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218 (United States)
  4. Department of Materials Science and Engineering, University of Wisconsin, 248 MS and E Building, 1509 University Avenue, Madison, Wisconsin 53706 (United States)
Publication Date:
OSTI Identifier:
22415158
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 106; Journal Issue: 3; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; AFFINITY; BUTYRIC ACID; CHARGE CARRIERS; DOPED MATERIALS; ENERGY GAP; ESTERS; HETEROJUNCTIONS; ORGANIC SOLAR CELLS; PHOTOVOLTAIC EFFECT; SUBSTRATES; WORK FUNCTIONS