Study of the dynamics of spin-dependent charge carrier recombination in Tris(8-hydroxyquinolinato) aluminium (Alq₃) with pulsed electrically detected magnetic resonance

We have studied the dynamics of previously reported spin-dependent charge carrier recombination transitions in Tris(8-hydroxyquinolinato) aluminium (Alq₃) [1] thin films with both continuous wave [2] as well as pulsed [3] electrically detected magnetic resonance (EDMR) spectroscopy under bipolar injection conditions. The measurements revealed transverse charge carrier spin relaxation times, T₂ shorter, but of the same order of magnitude to those previously observed in other organic semiconductors thin films such as various π-conjugated polymers, spin-orbit induced g-strain of the charge carrier magnetic resonances, as well as the local hyperfine field distribution magnitudes of both the electrons and the holes. Our measurements show that, qualitatively, the nature of spin-dependent recombination transitions in Alq₃ film is similar to that of the polymer materials and metal-organic complex Zinc phthalocyanine(ZnPc) [4]. [1] C.F.O. Graeff et al., Eur. Phys. J. E, 18, 21 (2005); [2] G Joshi et al., Appl. Phys. Lett., 109, 103303 (2016); [3] D. R. McCamey et al., Nature Mat., 7, 723 (2008); [4] S. Schaefer et al., phys. stat. sol. (b) 245 (10) 2120 (2008).