High-Performance W-Doped Bi0.5Sb1.5Te3 Flexible Thermoelectric Films and Generators.

Bi-Sb-Te-based thermoelectric materials have the best room-temperature thermoelectric properties, but their inherent brittleness and rigidity limit their application in the wearable field. In this study, W-doped p-type Bi0.5Sb1.5Te3 (W-BST) thin films were prepared using magnetron sputtering on polyimide substrates to create thermoelectric generators (TEGs). Bending tests showed that the thin film has excellent flexibility and mechanical durability, meeting the flexible requirements of wearable devices. W doping can significantly increase the carrier concentration, Seebeck coefficient, and electrical conductivity of BST thin films. At 300 K, the power factor of the W-BST film is 2.25 times higher than that of the undoped film, reaching 13.75 µW cm-1 K-2. First-principles calculations showed that W doping introduces significant impurity peaks in the bandgap, in which W d electrons remarkably hybridize with the Sb and Te p electrons, leading to an improved electrical conductivity of BST films. Furthermore, W doping significantly reduces the work function of BST films, thereby improving the carrier mobility. A TEG module fabricated from four layers of W-BST thin films achieved a maximum output power density of 6.91 mW cm-2 at a temperature difference of 60 K. Application tests showed that the flexible TEG module could power a portable clock using the temperature difference between body temperature and room temperature. At a medium temperature of 439 K, the assembled TEG module can provide a stable output voltage of 1.51 V to power a LED. This study demonstrates the feasibility of combining inorganic thermoelectric materials with flexible substrates to create high-performance flexible TEGs.

Isolation and cytotoxic activity of selaginellin derivatives and biflavonoids from Selaginella tamariscina.

Five selaginellin derivatives, including two new selaginellins termed selaginellins M (1) and N (2), and three previously identified compounds, selaginellin (3), selaginellin A (4), and selaginellin C (5), were isolated from the Selaginella tamariscina (Beauv.) Spring plant. In addition, four known biflavonoids, namely neocryptomerin ( 6), hinokiflavone (7), pulvinatabiflavone (8), and 7''- O-methylamentoflavone (9), were also isolated. The structures of new compounds 1 and 2 were elucidated by spectroscopic analysis. The cytotoxic activity of compounds 1- 9 was evaluated against a small panel of human cancer cell lines, including U251 (human glioma cells), HeLa (human cervical carcinoma cells), and MCF-7 (human breast cancer cells). The two new selaginellins, selaginellins M (1) and N (2), showed medium activity against the human cancer cell lines.