We investigate the steady-state out-of-plane spin diffusion in p-type bilayer WSe2 in the presence of the Rashba spin-orbit coupling and Hartree-Fock effective magnetic field. The out-of-plane components of the Rashba spin-orbit coupling serve as the opposite Zeeman-like fields in the two valleys. Together with the identical Hartree-Fock effective magnetic fields, different total effective magnetic field strengths in the two valleys are obtained. It is further revealed that due to the valley-dependent total effective magnetic field strength, similar (different) spin-diffusion lengths in the two valleys are observed at small (large) spin injection. Nevertheless, it is shown that the intervalley hole-phonon scattering can suppress the difference in the spin-diffusion lengths at large spin injection due to the spin-conserving intervalley charge transfers with the opposite transfer directions between spin-up and -down holes. Moreover, with a fixed large pure spin injection, we predict the build-up of a steady-state valley polarization during the spin diffusion with the maximum along the diffusion direction being capable of exceeding 1 %. It is revealed that the valley polarization arises from the induced quasi hot-hole Fermi distributions with different effective hot-hole temperatures between spin-up and -down holes during the spin diffusion, leading to the different intervalley charge transfer rates in the opposite transfer directions. Additionally, it is also shown that by increasing the injected spin polarization, the hole density or the impurity density, the larger valley polarization can be obtained.
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