Efficient Charge Carrier Injection and Balance Achieved by Low Electrochemical Doping in Solution-Processed Polymer Light-Emitting Diodes

Hao Yan, Saurav Limbu, Xuhua Wang, James Nightingale, Iain Hamilton, Jessica Wade, Sooncheol Kwon, Kwanghee Lee, Ji Seon Kim

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

Charge carrier injection and transport in polymer light-emitting diodes (PLEDs) is strongly limited by the energy level offset at organic/(in)organic interfaces and the mismatch in electron and hole mobilities. Herein, these limitations are overcome via electrochemical doping of a light-emitting polymer. Less than 1 wt% of doping agent is enough to effectively tune charge injection and balance and hence significantly improve PLED performance. For thick single-layer (1.2 µm) PLEDs, dramatic reductions in current and luminance turn-on voltages (VJ = 11.6 V from 20.0 V and VL = 12.7 V from 19.8 V with/without doping) accompanied by reduced efficiency roll-off are observed. For thinner (<100 nm) PLEDs, electrochemical doping removes a thickness dependence on VJ and VL, enabling homogeneous electroluminescence emission in large-area doped devices. Such efficient charge injection and balance properties achieved in doped PLEDs are attributed to a strong electrochemical interaction between the polymer and the doping agents, which is probed by in situ electric-field-dependent Raman spectroscopy combined with further electrical and energetic analysis. This approach to control charge injection and balance in solution-processed PLEDs by low electrochemical doping provides a simple yet feasible strategy for developing high-quality and efficient lighting applications that are fully compatible with printing technologies.

Original languageEnglish
Article number1904092
JournalAdvanced Functional Materials
Volume29
Issue number40
DOIs
StatePublished - 1 Oct 2019

Keywords

  • charge injection and balance
  • electrochemical doping
  • organic light-emitting diodes
  • organic semiconductors
  • solid-state ionic liquids

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