The conversion of sunlight into electricity has been dominated by photovoltaic and solar thermal power generation. Photovoltaic cells are deployed widely, mostly as flat panels, whereas solar thermal electricity generation relying on optical concentrators and mechanical heat engines is only seen in large-scale power plants. Here we demonstrate a promising flat-panel solar thermal to electric power conversion technology based on the Seebeck effect and high thermal concentration, thus enabling wider applications. The developed solar thermoelectric generators (STEGs) achieved a peak efficiency of 4.6% under AM1.5G (1 kW m(-2)) conditions. The efficiency is 7-8 times higher than the previously reported best value for a flat-panel STEG, and is enabled by the use of high-performance nanostructured thermoelectric materials and spectrally-selective solar absorbers in an innovative design that exploits high thermal concentration in an evacuated environment. Our work opens up a promising new approach which has the potential to achieve cost-effective conversion of solar energy into electricity.

Spectrally-selective solar absorbers harvest solar energy in the form of heat. Solar absorbers using cermet-based coatings demonstrate a high absorptance of the solar spectrum and a low emittance in the infrared (IR) regime. Extensive work has been done to optimize cermet-based solar absorbers to achieve high performance by exploring different cermet (ceramic-metal composite) materials and film configurations through different preparation techniques such as electrodeposition, sputtering, pulsed laser deposition, and solution-based methods. In this article, we review the progress of cermet-based spectrally-selective absorbers with high solar absorptance and low thermal emittance, such as Cr 2 O 3 , Al 2 O 3 , AlN, SiO 2 , and ZrO 2 based cermets as absorption layers. We also present an outlook for cermet-based spectrally-selective absorbers with high thermal stability and high conversion efficiency from sunlight to heat.

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10Bismuth telluride (Bi 2 Te 3 ) and its alloys have been widely investigated as thermoelectric materials for cooling applications at around room temperature. We report a systematic study on many compounds in the Bi 2 Te 3 -Bi 2 Se 3 -Bi 2 S 3 system. All the samples were fabricated by high energy ball milling followed with hot pressing. Among the investigated compounds, Bi 2 Te 2 S 1 shows a peak ZT ~0.8 at 300 o C 15 and Bi 2 Se 1 S 2 ~0.8 at 500 o C. These results show that these compounds can be used for mid-temperature power generation applications. The leg efficiency of thermoelectric conversion for segmented elements based on these n-type materials could potentially reach 12.5% with cold side at 25 o C and hot side at 500 o C if appropriate p-type legs are paired, which could compete well with the state-of-the-art ntype materials within the same temperature range, including lead tellurides, lead selenides, lead sulfides, filled-skutterudites, and half Heuslers. 20 Broader ContextThermoelectric convertor has provided a new class of green energy from solar heat, terrestrial heat, waste heat from both automobile vehicles and industrial operations. Bi 2 Te 3 -based materials have distinguished themself in low-temperature power generation applications. For these applications, the hot side temperature is typically limited to less than 250 o C due to the declining ZT value. For the mid-25 temperature range, PbTe and skutterudite materials were being considered as the candidates. However, the toxicity or thermal stability issue is still the most worrying part for these materials. In this work, we proposed an alternative way by using a segmented leg made from Bi 2 (Te, Se, S) 3 -based materials, which shows a potential leg efficiency of 12.5% with cold side of 25 o C and hot side of 500 o C. It competes well with the state-of-the-art n-type materials within the same temperature range. Specifically, two new compounds, i.e., Bi 2 Te 2 S 1 and Bi 2 Se 1 S 2 , have been identified as the promising materials for the mid-temperature applications.

Concentrating solar power normally employs mechanical heat engines and is thus only used in large-scale power plants; however, it is compatible with inexpensive thermal storage enabling electricity dispatchability. Concentrating solar thermoelectric generators (STEGs) have the advantage of replacing the mechanical power block with a solid-state heat engine based on the Seebeck effect, simplifying the system. The highest reported efficiency of STEGs so far is 5.2%. Here, we report experimental measurements of STEGs with a peak efficiency of 9.6% at an optically concentrated normal solar irradiance of 211 kW m -2 , and a system efficiency of 7.4% after considering optical concentration losses. The performance improvement is achieved by the use of segmented thermoelectric legs, a high-temperature spectrally-selective solar absorber enabling stable vacuum operation with absorber temperatures up to 600°C, and combining optical and thermal concentration. Our work suggests that concentrating STEGs have the potential to become a promising alternative solar energy technology.