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n–Doping of a Low–Electron–Affinity Polymer Used as an Electron–Transport Layer in Organic Light–Emitting Diodes

Journal Article · · Advanced Functional Materials
 [1];  [2];  [3];  [3];  [2];  [3];  [2]
  1. Princeton Univ., NJ (United States); Princeton University
  2. Princeton Univ., NJ (United States)
  3. Georgia Inst. of Technology, Atlanta, GA (United States)
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n-Doping electron-transport layers (ETLs) increases their conductivity and improves electron injection into organic light-emitting diodes (OLEDs). Because of the low electron affinity and large bandgaps of ETLs used in green and blue OLEDs, n-doping has been notoriously more difficult for these materials. In this work, n-doping of the polymer poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,7-diyl)] (F8BT) is demonstrated via solution processing, using the air-stable n-dopant (pentamethylcyclopentadienyl)(1,3,5-trimethylbenzene)ruthenium dimer [RuCp*Mes]2. Undoped and doped F8BT films are characterized using ultraviolet and inverse photoelectron spectroscopy. The ionization energy and electron affinity of the undoped F8BT are found to be 5.8 and 2.8 eV, respectively. Upon doping F8BT with [RuCp*Mes]2, the Fermi level shifts to within 0.25 eV of the F8BT lowest unoccupied molecular orbital, which is indicative of n-doping. Conductivity measurements reveal a four orders of magnitude increase in the conductivity upon doping and irradiation with ultraviolet light. Here, the [RuCp*Mes]2-doped F8BT films are incorporated as an ETL into phosphorescent green OLEDs, and the luminance is improved by three orders of magnitude when compared to identical devices with an undoped F8BT ETL.

Research Organization:
Princeton Univ., NJ (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0012458
OSTI ID:
1923743
Alternate ID(s):
OSTI ID: 1802352
OSTI ID: 1601907
Journal Information:
Advanced Functional Materials, Journal Name: Advanced Functional Materials Journal Issue: 17 Vol. 30; ISSN 1616-301X
Publisher:
WileyCopyright Statement
Country of Publication:
United States
Language:
English

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Figures / Tables (6)

Figure 1(p. 16)figure Figure 1
Figure 2(p. 17)figure Figure 2
Figure 3(p. 18)figure Figure 3
Figure 4(p. 19)figure Figure 4
Figure 5(p. 20)figure Figure 5
Figure 6(p. 21)figure Figure 6

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Related Subjects

36 MATERIALS SCIENCE
OLEDs
conductivity
electron-transport layers
low-electron-affinity polymers n-doping
n-doping
organic light-emitting diodes
organic semiconductors