Effects of isomeric transformation on characteristics of Alq3 amorphous layers prepared by vacuum deposition at various substrate temperatures

Abstract

Organic tris͑8-hydroxyquinoline͒aluminum ͑Alq3͒ amorphous layers are prepared by vacuum deposition at various substrate temperatures T sub from 30 to 180°C. The surface morphology and electrical characteristics of these as-deposited layers are studied by atomic force microscopy and current-density versus electric-field ͑J-E͒ curves. The temperature dependence of the dark electrical conductivity ͑T͒ determined from J-E curves is also examined. These experimental results reveal that the surface and electrical properties of Alq3 amorphous layers deposited at T sub between 90 and 120°C exhibit an anomalous T sub dependence. However, this anomalous T sub dependence is not observed from infrared absorption measurements, and therefore is not the result of chemical degradation. The observed behavior is explained in terms of the property that the vacuum deposition of Alq3 with T sub between 90 and 120°C involves a thermal interconversion between meridional and facial Alq3 isomers.

Crystalline phase in Alq3 films grown by the hot-wall method

“…It should be pointed out here that there are two possible explanations of the blue shift: one is crystallization of the film as discussed above, the other is due to the isomeric transformation between mer and fac isomers [8]. According to a study using the density functional theory, the isomeric transformation between mer and fac isomers leads to a high energy shift by 0.17 eV [15].…”

“…A thermal interconversion between these two isomers in Alq 3 films deposited by a conventional evaporation technique has been reported [8]. For crystalline Alq 3 five crystalline phases, a,b,g,d and e, have been identified in recent years [7,9,10].…”

Effects of source and substrate temperatures on the properties of ITO/CuPc/C60 heterostructure prepared by physical vapor deposition

“…From a crystal grower's point of view, during PVD processes, both T sou and T sub markedly affect the qualities of the asdeposited films, and these effects were clearly exhibited by our earlier experimental results on C 60 polycrystalline films [19,20] and tris(8-hydroxyquinoline)aluminum (Alq 3 ) amorphous layers [21,22]. To extend these experimental findings from a single layer structure to a sophisticated and complicated optoelectronic heterostructure, the effects of T sou and T sub on the performance of OPV cells with a heterostructure of ITO/CuPc/C 60 /Ag prepared by PVD were studied.…”

Re-condensation and decomposition of Tris(8-hydroxyquinoline)-aluminum in a vapor transport ampoule

“…However, due to the complexity that Alq 3 molecule has two geometrical isomers, meridional (mer-Alq 3 ) and facial (fac-Alq 3 ), and can aggregate into five different crystalline phases [9][10][11][12], the effect of changing growth conditions on the morphology and the electrical and optical properties of the as-prepared Alq 3 films and nanostructures remains an interesting topic to be investigated [13][14][15][16][17][18].…”