Enhanced thermoelectric performance of mechanically hard nano-crystalline-sputtered SnSe thin film compared to the bulk of SnSe

Thermoelectric thin-film architecture has the advantage over bulk by reducing further the thermal conductivity and increasing the figure of merit. The present work demonstrates the structural requirement to enhance the figure of merit and hardness of a SnSe thin film over bulk. The SnSe thin films were deposited over the glass substrate at different substrate temperatures (Ts) using the magnetron-sputtering technique. The bulk and the deposited films of SnSe were characterized by XRD, SEM, EDS, Raman spectroscopy, HRTEM, Nano-indentation, and thermoelectric properties (Seebeck coefficient, electrical, and thermal conductivities) measurement techniques. The structural, compositional, thermoelectrical, and mechanical analyses of films were used to establish the structure–property relationship for SnSe. The microstructure of the SnSe films was significantly affected by Ts. The well-evolved single-phase polycrystalline structure of the SnSe films was observed at high Ts (≥ 400 °C). The planar orientations overlapping induced dislocations were observed at high Ts. The maximum ZT (0.83), power factor (~ 2.43 µWcm⁻¹ K⁻²), and hardness (7.1 GPa) values were obtained for the SnSe film deposited at Ts = 500 °C. The structural modifications of SnSe thin film at high temperatures implemented by nano-crystallization, preferred orientation (111), grain boundaries, and competitive growth-induced dislocations were responsible for enhancing the figure of merit and hardness compared to bulk SnSe.