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

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 (Cs 2 CO 3 ) doping for organic light emitting devices. The current-voltage and light emission characteristics were measured as a function of the Cs 2 CO 3 doped ETL thickness at both room temperature and cryogenic (10–300 K). The current density (J) for the Alq:Cs 2 CO 3 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:Cs 2 CO 3 ETL device did not saturate for increasing ETL thicknesses confirming the TPBI:Cs 2 CO 3 devices have a near-ohmic cathode contact. The correlation of current density–voltage ( J – V ) and luminance-voltage ( L – V ) for both Alq:Cs 2 CO 3 and TPBI:Cs 2 CO 3 devices were studied over temperatures from 10 to 300 K. Both increased with increasing temperature; however, Cs 2 CO 3 -doped TPBI devices were more effective than Cs 2 CO 3 -doped Alq devices. The observed differences between Alq and TPBI may be attributed to the exposed nitrogen electron pair in the electronic structure. [ABSTRACT FROM AUTHOR]