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

Abstract

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.

Enhancement of solar absorption by a surface-roughened metal–dielectric film structure

“…The sputtering powers of the SiO 2 and Cr layers were fixed at 150 and 30 W, respectively, while that of the Cu layer was set to 30 or 150 W to obtain Cu layers with a smooth or rough surface, respectively. 8) The growth rates of the Cu and Cr layers were calibrated using a step profiler, while that of the SiO 2 layer was determined using a spectroscopic ellipsometer.…”

“…[4][5][6][7] In particular, the predicted solar-to-thermal-toelectric conversion efficiency of the solar thermophotovoltaics and solar thermoelectrics shows the potential to surpass the Shockley-Queisser limit of conventional photovoltaic solar cells. [5][6][7][8] In the solar-to-thermal conversion process, the solar selective absorber is the crucial component for absorbing most of the solar radiation energy in a broad wavelength region of 250-2500 nm while suppressing the infrared reradiation (>2.5 µm), which is induced by heating the absorber. The physical criteria of the solar absorptance α and thermal emittance ε are usually employed to characterize the performance of the solar absorber, where α is referred to as the weighted fraction of the absorbed energy compared with the incoming solar radiation, while ε is defined as the weighted fraction of the thermally emitted radiation with respect to Planck's blackbody distribution.…”