Broad-Temperature\nThermoelectric Figure of Merit Enhancement\nin Unconventional n‑Type Bi<sub>2</sub>Te<sub>2.3</sub>Se<sub>0.7</sub> Alloys

Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub>-based\nalloys are\nconventional n-type thermoelectric materials for solid-state cooling\nand heat harvest near room temperature; high thermoelectric performance\nover a wide temperature range and superior mechanical properties are\nessential for their use in practical thermoelectric devices. In this\nwork, we demonstrated that decent thermoelectric performance can also\nbe realized in an unconventional composite with a nominal composition\nof Bi<sub>2</sub>Te<sub>2.3</sub>Se<sub>0.7</sub> since the emergence\nof a Bi<sub>2</sub>Te<sub>2</sub>Se phase with Se ordered occupation\ncould induce an enlargement of the electronic band gap. Follow-up\nCu/Na codoping could generate a dynamic optimization of carrier concentration,\nsignificantly broadening the temperature range of high thermoelectric\nperformance. Further B incorporation and annealing treatment resulted\nin obvious grain refinement and stacking fault structures, which help\npushing the ultimate maximal figure of merit up to ∼1.3 at\n423 K with an average value of ∼1.2 at 300–573 K. This\nwork might provide insights for further research on bismuth tellurides\nand other thermoelectric materials.