Anomalous variation of electrical transport property and amorphization in dense Alq3

Abstract

Herein, we report the intriguing electrical transport and structural properties of compressed Alq₃, which is an extensively used electron transport material in OLEDs. The bulk resistance (R_b) of Alq₃ increases with uploading pressure, but drops markedly when the uploading pressure is above 8.6 GPa. In contrast, the grain boundary resistance (R_gb) varies smoothly below 16.4 GPa. With further compression, both R_b and R_gb increase with the amorphization of Alq₃. The pressure-induced amorphization is found to be reversible at a low density amorphous state, while it is irreversible at a higher density state. Interestingly, XRD measurements indicate no structural transition at ∼8.0 GPa. The variation of R_b is found to be synchronous with the blue-shift of the Al–oxine deformation mode, which rationalizes the anomalous changes of R_b. The Al–oxine interaction is believed to be also significant in the electrical transport properties of dense Alq₃, which provides insight into the correlation between its structural changes and electrical transport properties.