Abstract
Thermoelectrics operating at high temperature can cost-effectively convert waste heat and compete with other zero-carbon technologies. Among different high-temperature thermoelectrics materials, silicon nanowires possess the combined attributes of cost effectiveness and mature manufacturing infrastructures. Despite significant breakthroughs in silicon nanowires based thermoelectrics for waste heat conversion, the figure of merit (ZT) or operating temperature has remained low. Here, we report the synthesis of large-area, wafer-scale arrays of porous silicon nanowires with ultra-thin Si crystallite size of ~4 nm. Concurrent measurements of thermal conductivity (κ), electrical conductivity (σ), and Seebeck coefficient (S) on the same nanowire show a ZT of 0.71 at 700 K, which is more than ~18 times higher than bulk Si. This ZT value is more than two times higher than any nanostructured Si-based thermoelectrics reported in the literature at 700 K. Experimental data and theoretical modeling demonstrate that this work has the potential to achieve a ZT of ~1 at 1000 K.
Highlights
Thermoelectrics operating at high temperature can cost-effectively convert waste heat and compete with other zero-carbon technologies
The porosity (φ) of silicon nanowires (SiNWs) was varied from ~9% to 61% (Fig. 1e, f) by varying the doping concentration of starting Si wafer and metalassisted chemical etching (MACE) etching conditions, and the porosity was determined by the gravimetric measurement method
Our experimental data and theoretical model show that κ, σ, and S are relatively independent of temperature for the best performing SiNW (Figs. 2 and 3), making Z independent of temperature (Supplementary Fig. 12)
Summary
Thermoelectrics operating at high temperature can cost-effectively convert waste heat and compete with other zero-carbon technologies. Among different high-temperature thermoelectrics materials, silicon nanowires possess the combined attributes of cost effectiveness and mature manufacturing infrastructures. Despite significant breakthroughs in silicon nanowires based thermoelectrics for waste heat conversion, the figure of merit (ZT) or operating temperature has remained low. Waste heat above 573 K has the highest Carnot potential (>50%) to be converted to electricity due to higher Carnot efficiency[1]. Technoeconomic analysis[2] shows that thermoelectrics (TE) operating above 573 K can cost-effectively convert waste heat and compete with other zero carbon and waste heat conversion technologies. Among different hightemperature TE materials proposed[4,5,6,7], silicon nanowires (SiNWs)[8,9] possess the attributes to solve these challenges. This changed in 2008 when researchers reported that SiNW with rough surfaces or thin
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