A theoretical model to study Hanle effect for materials with weak spin-orbit coupling is developed. It considers the contributions from not only the drift current but also the diffusion part, which pronouncedly enlarges the application scope of the model. The spin lifetime in spin drift diffusion equation is also corrected by considering the thermal effect and the influence of external electrical field.

The spin-dependent electronical conductivity of polarons is studied in the spin polarized organic semiconductor .It is found that the spin dependence of the electronical conductivity is induced by the spin polarization of the organic semiconductor, for the spin polarization makes the up-spin and the down-spin polarons have different density, which generates the spin-dependent electronocal conductivity. The spin-dependent electrical conductivity can be directly affected by the match level of conductivities s0/sf at the interface of the FM/OSE. Moreover, the current spin polarization in the organic semiconductor can be strengthened by the electric-field in the low-electric-field region .

Spin dephasing in organic semiconductor was studied based on spin drift-diffusion model in various electric field. It is found that in the ohmic regime, spin dephasing is determined by the voltage bias. With increase of the voltage bias, spin coherence increases. And the increasing voltage bias can enhance the magnitude of the spin dephasing oscillations at a static perpendicular maganetic field. It shows that the current density in total device output can be modulated by an electrostatic field via controlled precession.

The spin injection efficiency in the ferromagnet/ organic semiconductors system (FM/OSE) was studied under an external electric-field. It is found that the spin injection efficiency can be strongly influenced by the spin-dependent electrical conductivity and the downstream spin diffusion length of polarons. With the increase of external electric-field, the downstream spin diffusion length increases and makes the spin-dependent electrical conductivity increase, too. So the spin injection efficiency is enhanced. When the external electric-field increases from 1 to 10 mV/μm at T=80K, the spin injection efficiency increases about 20%. It seems that the downstream spin diffusion length is an significant factor to affect the spin injection efficiency in the FM/ OSE under an external electric-field.

Spin diffusion in the finite magnetic heterojunction was explored considering the spin dependent conductivity. In organic semiconductor spintronic devices, the up-spin and down-spin polarons have different density once spin injection happens from ferromagnetic electrodes into organic semiconductors. The difference results in the spin dependent conductivity. The calculations show that the spin injection efficiency is dependent on the spin dependent conductivity and the size of the layers. The spin dependent conductivity has great influence on the spin injection efficiency in the finite magnetic heterojunction, when the spin polarization of the organic semiconductors is moderate.