Abstract: The morphology of the active layer has an important influence on the device efficiency of organic solar cells. Tuning the molecular orientation in the active layer is one of the ways to optimize its morphology. This paper aims to use a Layer-by-Layer (LbL) method to regulate the orientation of molecules in the active layer of organic solar cells, thereby improving the efficiency of cell devices. By adding different additives to the electron acceptor, the orientation of acceptor molecule (Y6) in the active layer is adjusted, and the energy conversion efficiency of the optimized device reaches 16.2%. The active layer films were characterized by ellipsometry and grazing incidence wide-angle X-ray scattering (GIWAXS). The results show that after adding 1,8-diiooctane (DIO) as an additive to the receptor, Y6 molecules in the active layer tend to be horizontally oriented, and after adding chloronaphthalene (CN) as an additive to the receptor, Y6 molecules tend to be vertically oriented. The electrical and optical characterization results show that the horizontal orientation of Y6 increases the exciton separation efficiency, and then improves the energy conversion efficiency of the device.