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

Hannah L. Smith, Jordan T. Dull, Swagat K. Mohapatra, Khaled Al Kurdi, Stephen Barlow, Seth R. Marder, Barry P. Rand, Antoine Kahn

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish (US)
Pages (from-to)2381-2389
Number of pages9
JournalACS Applied Materials and Interfaces
Volume14
Issue number1
DOIs
StatePublished - Jan 12 2022

All Science Journal Classification (ASJC) codes

  • Materials Science(all)

Keywords

  • light emission
  • n-dopants
  • organic semiconductors
  • p-dopants
  • p-i-n homojunctions
  • photoemission spectroscopy

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