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Powerful Organic Molecular Oxidants and Reductants Enable Ambipolar Injection in a Large-Gap Organic Homojunction Diode

Author(s): Smith, Hannah L; Dull, Jordan T; Mohapatra, Swagat K; Al Kurdi, Khaled; Barlow, Stephen; et al

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Abstract: Doping has proven to be a critical tool for enhancing the performance of organic semiconductors in devices like organic light-emitting diodes. However, the challenge in working with high-ionization-energy (IE) organic semiconductors is to find p-dopants with correspondingly high electron affinity (EA) that will improve the conductivity and charge carrier transport in a film. Here, we use an oxidant that has been recently recognized to be a very strong p-type dopant, hexacyano-1,2,3-trimethylene-cyclopropane (CN6-CP). The EA of CN6-CP has been previously estimated via cyclic voltammetry to be 5.87 eV, almost 300 meV higher than other known high-EA organic molecular oxidants. We measure the frontier orbitals of CN6-CP using ultraviolet and inverse photoemission spectroscopy techniques and confirm a high EA value of 5.88 eV in the condensed phase. The introduction of CN6-CP in a film of large-band-gap, large-IE phenyldi(pyren-1-yl)phosphine oxide (POPy2) leads to a significant shift of the Fermi level toward the highest occupied molecular orbital and a 2 orders of magnitude increase in conductivity. Using CN6-CP and n-dopant (pentamethylcyclopentadienyl)(1,3,5-trimethylbenzene)ruthenium (RuCp*Mes)2, we fabricate a POPy2-based rectifying p–i–n homojunction diode with a 2.9 V built-in potential. Blue light emission is achieved under forward bias. This effect demonstrates the dopant-enabled hole injection from the CN6-CP-doped layer and electron injection from the (RuCp*Mes)2-doped layer in the diode.
Publication Date: 3-Jan-2022
Citation: Smith, Hannah L, Dull, Jordan T, Mohapatra, Swagat K, Al Kurdi, Khaled, Barlow, Stephen, Marder, Seth R, Rand, Barry P, Kahn, Antoine. (2022). Powerful Organic Molecular Oxidants and Reductants Enable Ambipolar Injection in a Large-Gap Organic Homojunction Diode. ACS Applied Materials & Interfaces, 14 (1), 2381 - 2389. doi:10.1021/acsami.1c21302
DOI: doi:10.1021/acsami.1c21302
ISSN: 1944-8244
EISSN: 1944-8252
Pages: 2381 - 2389
Language: en
Type of Material: Journal Article
Journal/Proceeding Title: ACS Applied Materials & Interfaces
Version: Author's manuscript

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