2D Self-Assembly of Large-Sized Inorganic Nanosheets Leading to Enhanced Power Factors in Earth-Abundant Cu₃SbSe₄-Based Flexible Hybrid Films

Fabrication of large-sized inorganic nanosheets is an efficient strategy to promote carrier transportation in flexible thermoelectric (TE) films. Herein, we report the self-assembly of large-sized Cu 3 SbSe 4 nanosheets by using a Se nanowire template via wet chemical synthesis and then vacuum-assisted filter these plate-like microcrystals on nylon to prepare Cu 3 SbSe 4 flexible thermoelectric (TE) hybrid films. SEM reveals that the as-synthesized Cu 3 SbSe 4 powders by using Se nanowires as selenium sources presented 2D plate-like micron structures uniformly and tightly self-assembled by acute triangle-like nanoparticles. Furthermore, XPS evidences that extra Sb vacancies are generated in the unit cell of Cu 3 SbSe 4 crystals synthesized by using the Se NW template, resulting in the shrinkage of the unit cell and the narrowing interplanar spacing, which are characterized by XRD and TEM. As a result, both carrier concentration and carrier mobility have been significantly improved. The high carrier concentration is proved to originate from the extra carriers induced by Sb vacancies, and the high carrier mobility of the film is mainly ascribed to its continuous grain boundaries in the plate-like microcrystal morphology. The large-sized nanosheet Cu 3 SbSe 4 /nylon hybrid film (CSS MPs) exhibits a high power factor (PF) of 235.45 μW m –1 K –2 at 400 K, which is 4.23 times higher than that of the Cu 3 SbSe 4 /nylon hybrid film (CSS NPs) where Cu 3 SbSe 4 crystals are synthesized by using raw Se particles. This work reveals a novel approach to prepare plate-like Se-based semiconductors, which requires both high carrier concentration and high carrier mobility.