<p>Bismuth chalcogenide-based materials have attracted attention for room-temperature thermoelectric applications because of their favorable electronic transport properties; however, controlling defects, anisotropy, and carrier transport in thin films remains challenging. In this study, BiTeSe thin films are systematically investigated as a promising <i>n</i>-type thermoelectric material, with a focus on the effect of post-selenization time on structural and transport properties. X-ray diffraction confirms the formation of the BiTeSe phase, while shoulder peaks indicate minor impurities or defect-related features. Increasing post-selenization time significantly influences crystallite size, dislocation density, and microstrain, reflecting progressive structural evolution. Surface morphology analysis shows increased roughness and grain refinement with prolonged selenization, indicating improved film densification. Electrical measurements reveal a notable decrease in resistivity up to 3&#xa0;h post-selenization, despite higher defect density, because of increased electron concentration and optimized carrier transport. Pronounced anisotropic Seebeck behavior correlates strongly with grain orientation, particularly in the 3&#xa0;h post-selenized sample. Variations in Fermi energy with selenization time highlight the combined effects of mechanical strain and anisotropy on transport. The thermoelectric power factor reaches 3.53&#xa0;μWcm⁻¹&#xa0;K⁻² for the 3&#xa0;h film, demonstrating that post-selenization effectively enhances performance. These results confirm the potential of BiTeSe films for efficient room-temperature thermoelectric applications.</p>