Thermoelectric superlattices are expected to decouple the strong correlation between various thermoelectric parameters, and are an important strategy for excellent thermoelectric performances. The superlattices of (Bi₂)_m(Bi₂Te₃)_n homologous series are well-known for low lattice thermal conductivity and intriguing topological surface states. However, the impacts of electronic structure on the thermoelectric performance were still not well-understood in (Bi₂)_m(Bi₂Te₃)_n. To cope with this issue, Bi₂–Bi₂Te₃ superlattice-like films with adjustable Bi₂/(Bi₂+Bi₂Te₃) molar ratio (R) were successfully fabricated by the molecular beam epitaxy technique. Angle-resolved photoemission spectroscopy measurements combined with theoretical calculations revealed the conduction band evolution from single-valley to multi-valley as R ≥ 0.30, leading to intrinsically high carrier effective mass and improved thermoelectric power factor. Also, the superlattice film (R = 0.46) with the structure close to Bi₄Te₃ possesses the topological surface state feature around the high symmetry point. As a result of the high effective mass of 3.9 m₀ and very high electron density of 2.31 × 10²¹ cm⁻³, the film with R = 0.46 acquired the highest power factor of 1.49 mW·m⁻¹·K⁻² at 420 K, outperforming that of other (Bi₂)_m(Bi₂Te₃)_n superlattices. This work lays an essential foundation on understanding the electronic structure and further improving thermoelectric performances of (Bi₂)_m(Bi₂Te₃)_n homologous series.