Hetero-interfaced films composed of solvothermally synthesized Bi2Te3 nanoplates covered with electrodeposited Bi2Se3 layers

In this study, hetero-interface-structured Bi2Te3-nanoplate/Bi2Se3-electrodeposited films were prepared using all solution processes. Single-crystalline Bi2Te3 nanoplates were synthesized using a solvothermal method, and Bi2Te3 nanoplate films were prepared by drop-casting followed by thermal annealing. The electrodeposition time of the Bi2Se3 layer was tuned to obtain hetero-interface-structured films, wherein the gap between the Bi2Te3 nanoplates was filled. Cross-sectional scanning electron microscopy showed that the heterointerface structured films had a boundary between the composite layer and the Bi2Te3-nanoplate film. The X-ray diffraction patterns of the hetero-interface-structured films without thermal annealing exhibited peaks arising from Bi2Te3, as well as Bi2Se3 with and without antisite defects (SeBi), while those of the annealed film exhibited peaks from Bi2Te3, Bi2Se3, and the ternary alloys due to mutual diffusion. The annealed hetero-interface-structured film with an electrodeposition time of 40 min exhibited the highest power factor of 1.70 μW/(cm·K2), which is 12-fold and 30% higher than that of the Bi2Te3-nanoplate and homo-interface-structured films (Bi2Te3-nanoplate/Bi2Te3-electrodeposited film), respectively. This enhancement was observed due to (a) increased electrical conductivity arising from the improved crystallinity of the Bi2Se3 electrodeposited layer and (b) increased Seebeck coefficient, resulting presumably from the combined effect of the heterostructured interface, decrease in the number of antisite defects, and formation of ternary alloys. Our findings provide a route for fabricating high-performance thermoelectric materials with low manufacturing costs.