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

Abstract

A B S T R A C TThe 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 luminancevoltage (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.Published by Elsevier B.V.

New Class of Wide Energy Gap Benzotriimidazole Optical Materials

“…Many materials containing benzimidazole are suitable for both emissive and charge transport layers in OLEDs. Among benzimidazole materials, one of the most useful and extensively utilized is 1,3,5-tris(Nphenylbenzimidazole-2-yl)benzene (TPBI) (Figure 1a) [21][22][23][24]. TPBI has a unique aromatic polycyclic core and ring structure features, which result in high thermal stability, chemical stability, and resistance to oxidation.…”

“…TPBI has a unique aromatic polycyclic core and ring structure features, which result in high thermal stability, chemical stability, and resistance to oxidation. TPBI and similar materials are commonly used as electron transporting, hole blocking layers within OLED devices [23,24]. In many cases, TPBI is also employed as part of an OLED's emissive layer as an electron transporting host material for fluorescent or phosphorescent dye molecules.…”