Inclusion of SCyclic, SLinear, and Na2S into chemically etched porous silicon matrix: Thermoelectric studies

The research discusses methods to enhance silicon's thermoelectric properties through embedding two allotropic forms of sulfur and sodium sulfide into chemically etched nanoporous silicon. The etching of technical-grade silicon powder (Si Powder ) was performed using an aqueous KOH/KF solution to yield hydrophilic/hydrophobic porous sites (p-Si). The porosity of p-Si was estimated by measuring the uptake of water and toluene at ambient conditions. These sites were extrinsically doped with linear and cyclic allotropes of elemental sulfur (S 8 ), and sodium sulfide to yield S linear : p-Si, S cyclic : p-Si, and Na 2 S: p-Si, respectively. The composition of the incorporated composites was examined by thermogravimetric analysis (TGA) in air, and their structural characteristics were investigated using P-XRD, ATR-IR, and SEM. The thermal, electrical, and thermoelectric (TE) properties (Seebeck coefficient, figure of merit, power factor) of these semiconductors were assessed as cold-pressed circular discs in the temperature range of 305 ≤ T ≤ 525. These inclusion composites exhibit ohmic semiconducting behavior, with thermal energy propagation via phonon lattice vibrations rather than electronic processes. Our findings reveal that the Na 2 S: p-Si and S linear : p-Si composites exhibit significant ZT values of ≈ 0.24 and 0.16, respectively, rendering them highly promising for TE applications in small-scale waste heat recovery from sunshine and small domestic devices.