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Spectral Signatures of a Negative Polaron in a Doped Polymer Semiconductor: Energy Levels and Hubbard U Interactions

Journal Article · · Journal of Physical Chemistry Letters
 [1];  [2];  [3];  [4];  [5];  [5];  [6];  [7];  [8];  [6];  [9];  [9];  [5];  [2];  [3];  [1]
  1. Princeton Univ., NJ (United States)
  2. Univ. of Kentucky, Lexington, KY (United States)
  3. Humboldt Univ. of Berlin (Germany); Helmholtz-Zentrum Berlin (HZB), (Germany). German Research Centre for Materials and Energy
  4. Humboldt Univ. of Berlin (Germany)
  5. Univ. of Arizona, Tucson, AZ (United States)
  6. Freie Univ., Berlin (Germany)
  7. Georgia Institute of Technology, Atlanta, GA (United States)
  8. Univ. of Colorado, Boulder, CO (United States)
  9. Georgia Institute of Technology, Atlanta, GA (United States); Univ. of Colorado, Boulder, CO (United States); National Renewable Energy Laboratory (NREL), Golden, CO (United States). Chemistry and Nanoscience Center
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The modern picture of negative charge carriers on conjugated polymers invokes the formation of a singly occupied (spin-up/spin-down) level within the polymer gap and a corresponding unoccupied level above the polymer conduction band edge. The energy splitting between these sublevels is related to on-site Coulomb interactions between electrons, commonly termed Hubbard U. However, spectral evidence for both sublevels and experimental access to the U value is still missing. Here, in this work, we provide evidence by n-doping the polymer P(NDI2OD-T2) with [RhCp*Cp]2, [N-DMBI]2, and cesium. Changes in the electronic structure after doping are studied with ultraviolet photoelectron and low-energy inverse photoemission spectroscopies (UPS, LEIPES). UPS data show an additional density of states (DOS) in the former empty polymer gap while LEIPES data show an additional DOS above the conduction band edge. These DOS are assigned to the singly occupied and unoccupied sublevels, allowing determination of a U value of ~1 eV.

Research Organization:
National Renewable Energy Laboratory (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); National Science Foundation (NSF); US Department of the Navy, Office of Naval Research (ONR)
Grant/Contract Number:
AC36-08GO28308; SC0012458; SC0023411
OSTI ID:
1986134
Alternate ID(s):
OSTI ID: 1996007
Report Number(s):
NREL/JA-5900-86070; MainId:86843; UUID:f16288e7-ab47-4759-8bfa-1a6a6da18574; MainAdminID:69821
Journal Information:
Journal of Physical Chemistry Letters, Journal Name: Journal of Physical Chemistry Letters Journal Issue: 24 Vol. 14; ISSN 1948-7185
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
conjugated polymers
n-doping
on-site Coulomb interaction
photoelectron spectroscopy
polarons