Date of this Version
Synthetic Metals 209 (2015) 128–134
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.