Simulating Spin Relaxation in Organic Semiconductors

Understanding spin lifetimes in organic semiconductors is important for spin-based applications as well as for devices like organic solar cells and OLEDs. Spin relaxation and diffusion in disordered organic semiconductors is explored with numerical simulations. Previous theories and simulations examined the role of nuclear and spin-orbit interactions in relaxing spin [1, 2]. This work extends and explores in more detail the influence of spin-orbit interactions. Spin relaxation is studied in two regimes: one in which hops are uncorrelated with each other (multiple trapping) and the other where hops are correlated (multiple hopping). For multiple trapping we find agreement with analytic solutions [1]. For multiple hopping we find the simulation gives a smaller spin relaxation rate (a factor of 2/3). Both models are studied in either the semi-classical approximation where the carrier spin is a classical vector or in a quantum model where the carrier spin is a quantum object. We find interesting differences emerge between the two approaches when the hopping rates depends on orbital alignment.

[1] N. J. Harmon, M. E. Flatté, Phys. Rev. B 90, 115203 (2014)
[2] S. R. McMillan, N. J. Harmon, M. E. Flatté, in review