Universal and solution-processable precursor to bismuth chalcogenide thermoelectrics

A solution processing technique that could enable low-cost production of thermoelectric devices with efficiencies comparable to conventionally fabricated devices, was studied. A bismuth sulfide precursor was created by reacting Bi₂S₃ sulfur, and distilled hydrazine. Thin films for characterization and transport measurements were made by spin-coating the precursors onto substrates. Bi₂Se₃ films were made by annealing the precursor at 250°C for 30 mm. To promote incorporation of tellurium into the compounds, the precursors for Bi,Te, Bi₂Te ₂Se, and Bi₂TeSe₂ were annealed at 400°C for 30 mm. Rutherford backscattering spectrometry and energy dispersive X-ray spectroscopy confirm the presence of the indicated elements and the absence of residual sulfur. All compounds exhibit a negative sign of thermopower, which indicates that these films are n-type semiconductors.