Anomalous variation of electrical transport property and amorphization in dense Alq3

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 (Rb) of Alq3 increases with uploading pressure, but drops markedly when the uploading pressure is above 8.6 GPa. In contrast, the grain boundary resistance (Rgb) varies smoothly below 16.4 GPa. With further compression, both Rb and Rgb 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 Rb is found to be synchronous with the blue-shift of the Al–oxine deformation mode, which rationalizes the anomalous changes of Rb. 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.