TY - JOUR
T1 - P-type doping of organic wide band gap materials by transition metal oxides
T2 - A case-study on Molybdenum trioxide
AU - Kröger, Michael
AU - Hamwi, Sami
AU - Meyer, Jens
AU - Riedl, Thomas
AU - Kowalsky, Wolfgang
AU - Kahn, Antoine
N1 - Funding Information:
Work at Princeton University was supported by the National Science Foundation (DMR-0705920). S.H., J.M., T.R. and W.K. gratefully acknowledge financial support by the German Federal Ministry for Education and Research BMBF (contract 13N8166A) and the Deutsche Forschungsgemeinschaft (DFG) through the Gottfried Wilhelm Leibniz award. M.K. acknowledges the German Academic Exchange Service (DAAD) for generous support within the post-doctoral fellowship program.
PY - 2009/8
Y1 - 2009/8
N2 - A study on p-doping of organic wide band gap materials with Molybdenum trioxide using current transport measurements, ultraviolet photoelectron spectroscopy and inverse photoelectron spectroscopy is presented. When MoO3 is co-evaporated with 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP), a significant increase in conductivity is observed, compared to intrinsic CBP thin films. This increase in conductivity is due to electron transfer from the highest occupied molecular orbital of the host molecules to very low lying unfilled states of embedded Mo3O9 clusters. The energy levels of these clusters are estimated by the energy levels of a neat MoO3 thin film with a work function of 6.86 eV, an electron affinity of 6.7 eV and an ionization energy of 9.68 eV. The Fermi level of MoO3-doped CBP and N,N′-bis(1-naphtyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (α-NPD) thin films rapidly shifts with increasing doping concentration towards the occupied states. Pinning of the Fermi level several 100 meV above the HOMO edge is observed for doping concentrations higher than 2 mol% and is explained in terms of a Gaussian density of HOMO states. We determine a relatively low dopant activation of ∼0.5%, which is due to Coulomb-trapping of hole carriers at the ionized dopant sites.
AB - A study on p-doping of organic wide band gap materials with Molybdenum trioxide using current transport measurements, ultraviolet photoelectron spectroscopy and inverse photoelectron spectroscopy is presented. When MoO3 is co-evaporated with 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP), a significant increase in conductivity is observed, compared to intrinsic CBP thin films. This increase in conductivity is due to electron transfer from the highest occupied molecular orbital of the host molecules to very low lying unfilled states of embedded Mo3O9 clusters. The energy levels of these clusters are estimated by the energy levels of a neat MoO3 thin film with a work function of 6.86 eV, an electron affinity of 6.7 eV and an ionization energy of 9.68 eV. The Fermi level of MoO3-doped CBP and N,N′-bis(1-naphtyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (α-NPD) thin films rapidly shifts with increasing doping concentration towards the occupied states. Pinning of the Fermi level several 100 meV above the HOMO edge is observed for doping concentrations higher than 2 mol% and is explained in terms of a Gaussian density of HOMO states. We determine a relatively low dopant activation of ∼0.5%, which is due to Coulomb-trapping of hole carriers at the ionized dopant sites.
KW - Charge transport
KW - Doping
KW - Electronic structures/processes/mechanisms
KW - Inverse photoelectron spectroscopy
KW - Organic electronics
KW - Ultraviolet photoelectron spectroscopy
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U2 - 10.1016/j.orgel.2009.05.007
DO - 10.1016/j.orgel.2009.05.007
M3 - Article
AN - SCOPUS:67649216558
SN - 1566-1199
VL - 10
SP - 932
EP - 938
JO - Organic Electronics
JF - Organic Electronics
IS - 5
ER -