Temperature dependence of cesium carbonate-doped electron transporting layers on organic light-emitting diodes

Authors

Richard Fu, U.S Army Research Laboratory, Adelphi, MD
Eric Forsythe, U.S Army Research Laboratory, Adelphi, MD
Jianmin Shi, U.S Army Research Laboratory, Adelphi, MD
Merric Srour, U.S Army Research Laboratory, Adelphi, MD
Steven Blomquist, U.S Army Research Laboratory, Adelphi, MD
David Morton, U.S Army Research Laboratory, Adelphi, MD

Date of this Version

2015

Citation

Synthetic Metals 209 (2015) 128–134

Abstract

The temperature dependence and electronic transport properties of 1, 3, 5-tri(1-phenyl-1H-benzo[d] imidazol-2-yl) phenyl (TPBI) and 8-hydroxyquinoline aluminum (Alq) electron transporting layers (ETL) have been investigated as a function of cesium carbonate (Cs₂CO₃) doping for organic light emitting devices. The current-voltage and light emission characteristics were measured as a function of the Cs₂CO₃ doped ETL thickness at both room temperature and cryogenic (10–300 K). The current density (J) for the Alq:Cs₂CO₃ ETL device increased for an ETL thickness between 100 and 300 Å, with no further increase in the ETL beyond 300 Å, indicating an electron injection limited contact. Conversely, the J for the TPBI: Cs₂CO₃ ETL device did not saturate for increasing ETL thicknesses confirming the TPBI:Cs₂CO₃ devices have a near-ohmic cathode contact. The correlation of current density–voltage (J–V) and luminancevoltage (L–V) for both Alq:Cs₂CO₃ and TPBI:Cs₂CO₃ devices were studied over temperatures from 10 to 300 K. Both increased with increasing temperature; however, Cs₂CO₃-doped TPBI devices were more effective than Cs₂CO₃-doped Alq devices. The observed differences between Alq and TPBI may be attributed to the exposed nitrogen electron pair in the electronic structure.