High photon-to-heat conversion efficiency in the wavelength region of 250-1200 nm based on a thermoelectric Bi₂Te₃ film structure

In this work, 4-layered SiO₂/Bi₂Te₃ /SiO₂/Cu film structures were designed and fabricated and the optical properties investigated in the wavelength region of 250-1200 nm for their promising applications for direct solar-thermal-electric conversion. A typical 4-layered film sample with the structure SiO₂(66.6 nm)/Bi₂Te₃ (7.0 nm)/SiO₂(67.0 nm)/Cu (>100.0 nm) was deposited on a Si or K9-glass substrate by magnetron sputtering. The experimental results agree well with the simulated ones showing an average optical absorption of 96.5%, except in the shorter wavelength region, 250-500 nm, which demonstrates the superior absorption property of the 4-layered film due to the randomly rough surface of the Cu layer resulting from the higher deposition power. The high reflectance of the film structure in the long wavelength region of 2-20 μm will result in a low thermal emittance, 0.064 at 600 K. The simpler 4-layered structure with the thermoelectric Bi₂Te₃ used as the absorption layer may provide a straightforward way to obtain solar-thermal-electric conversion more efficiently through future study.