Manifestation of geminate and bimolecular stages of triplet-exciton annihilation in the kinetics of singlet fission in organic semiconductors

•Short- and long-time parts of the kinetics of SF-processes in organic semiconductors are essentially determined by that of geminate and bimolecular stages of diffusion-assisted TT-annihilation.•The kinetics of T-diffusion-assisted SF-processes in organic semiconductors can be described in the wide range of times with the simple expression.•The slow long-time tail of the geminate TTA-kinetics noticeably manifest itself in the kinetics of SF-processes in organic semiconductors.