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

Journal Article · · ACS Applied Materials and Interfaces
ORCiD logo [1];  [2];  [3];  [4]; ORCiD logo [5]; ORCiD logo [5]; ORCiD logo [2]; ORCiD logo [2]
  1. Princeton Univ., NJ (United States); Princeton University
  2. Princeton Univ., NJ (United States)
  3. Georgia Inst. of Technology, Atlanta, GA (United States); Inst. of Chemical Technology─Indian Oil Odisha Campus, Odisha (India)
  4. Georgia Inst. of Technology, Atlanta, GA (United States)
  5. Georgia Inst. of Technology, Atlanta, GA (United States); Univ. of Colorado, Boulder, CO (United States)
+ Show Author Affiliations

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. Furthermore, 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.

Research Organization:
Princeton Univ., NJ (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0012458
OSTI ID:
1923742
Journal Information:
ACS Applied Materials and Interfaces, Journal Name: ACS Applied Materials and Interfaces Journal Issue: 1 Vol. 14; ISSN 1944-8244
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

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36 MATERIALS SCIENCE
deposition
diodes
electrical conductivity
layers
light emission
n-dopants
organic semiconductors
p-dopants
photoemission spectroscopy
p−i−n homojunctions
work function