Chiral organic semiconductors are promising for miniaturized and integrated circularly polarized light detection due to their spectral tunability and easy processing. In this paper, poly(3-hexylthiophene-block-poly(phenylisocyanide)) (P3HT₈₀ and P3HT₈₀-PPI(L)₃₀) were synthesized by controlled incorporation of chiral isonitrile (PPI). The experimental results demonstrated that two semiconductor polymers were successfully synthesized. Furthermore, the optical properties of the two semiconductor polymers were tested and the block polymer P3HT₈₀-PPI(L)₃₀ was found to have chiral optical activity. A circularly polarized photodetector based on an organic field effect transistor was prepared to study the performance of the device for differentiating the spin direction of circularly polarized light at 450 nm. The experimental results indicated that the addition of chiral isonitrile (PPI) degraded the electrical properties of P3HT₈₀ but introduced chiral optical activity, enabling the devices based on P3HT₈₀-PPI(L)₃₀ to distinguish the spin direction of circularly polarized light, and the photocurrent asymmetry factor gres at 450 nm reached 0.083.