This study demonstrates that thermoelectric power factor (PF) of B20-CoSi with a peculiar electronic band structure (Dirac-like band and heavy hole band) surprisingly gets high regardless of crystal quality. We reveal that the high PF is attributed to energy filtering effect in wavenumber space via electron-phonon interaction or similar scattering processes. The experimental temperature dependences of normalized Seebeck coefficients of epitaxial (fewer defects) and polycrystalline B20-CoSi films (more defects) were in agreement with the calculated ones using the relaxation time for electron-phonon interaction, proving that Seebeck coefficient is robust against crystal defects. Both epitaxial and polycrystalline films exhibited higher electrical conductivities than conventional thermoelectric materials because of pseudogap semimetals. As a result, the B20-CoSi films exhibited relatively high PF of about $20\mu {\mathrm{Wcm}}^{-1}{\mathrm{K}}^{-2}$ at room temperature, which was higher than those of promising silicide thermoelectric films. This study concludes that the robustness of Seebeck coefficient against crystal defects in the material with a peculiar EBS can lead to the realization of high performance thermoelectric materials.

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• Density of states
• Electrical conductivity
• Growth
• Phonons
• Seebeck effect
• Thermal conductivity
• Thermoelectric effects
• Epitaxy
• Molecular beam epitaxy