Carrier injection and bipolar transport in NPB for single-layers OLEDs

S. C. Tse, K. K. Tsung, Shu Kong SO

Research output: Chapter in book/report/conference proceedingConference proceedingpeer-review

4 Citations (Scopus)


We studied the carrier injection and transporting properties of N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4'diamine (NPB), a common hole transporter for organic light-emitting diodes (OLEDs). NPB was found to possess significant electron mobility from time-of-flight (TOF) measurement. With bipolar transporting ability, NPB was used to fabricate single-layer devices with a configuration of ITO/ PEDOT:PSS/ NPB/ Ca/ Ag. PEDOT:PSS was demonstrated to form a quasi-Ohmic contact to NPB by admittance spectroscopy (AS) and dark-injection space-charge-limited current (DISCLC) measurements. From current-voltage (JV) characteristics, single-layer NPB devices exhibited a bulk-limited hole current in low-voltage region. Electron injection was clearly observed at a turn-on voltage of about 4V, which coincided with the luminance-voltage measurement. In order to confine the recombination zone, dye-doped NPB layer was inserted into single-layer devices. This intentional doping technique made a notable improvement in current efficiency. The mechanisms of the doped devices were also addressed.

Original languageEnglish
Title of host publicationOrganic Light Emitting Materials and Devices XI
Publication statusPublished - 2007
EventOrganic Light Emitting Materials and Devices XI - San Diego, CA, United States
Duration: 26 Aug 200729 Aug 2007

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


ConferenceOrganic Light Emitting Materials and Devices XI
Country/TerritoryUnited States
CitySan Diego, CA

Scopus Subject Areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

User-Defined Keywords

  • Admittance spectroscopy
  • Bipolar transport
  • Charge injection
  • Organic light-emitting diodes


Dive into the research topics of 'Carrier injection and bipolar transport in NPB for single-layers OLEDs'. Together they form a unique fingerprint.

Cite this