Wet Chemical Treatment-Induced Kinked Cu₂Se-PbSe Nanaowires

The utilization of thermoelectric generation (TEG) to convert waste heat into electricity has emerged as an eco-friendly energy production method. Through the advancement of high-performance TE materials, waste heat can be effectively captured and transformed into a robust alternative energy source, offering solutions to emerging energy challenges across diverse applications. The development of selenium (Se) based thermoelectric devices has emerged as a promising alternative to tellurium (Te). Nevertheless, thermoelectric devices based on selenium typically exhibit lower power factor compared to tellurium-based devices. Overcoming this performance gap necessitates a more sophisticated engineering approach.<br/>In this study, we increase the thermoelectric efficiency through nano-structuring and doping strategies. Initially, ZnSe nanowires were grown using the Solution-Solid-Solid (SSS) method with Ag₂Se catalysts. During the growth procedure, NH₄l was added to reduce the reactivity of the zinc precursor, resulting in the formation of numerous stacking faults(SFs). The accumulation of SFs led to the glide of the {111} plane in the zincblende (ZB) phase of ZnSe nanowires, resulting in a zigzag morphology known as a kinked structure. Subsequently, we implemented the Regiospecific Sequential Cation Exchange (RSCE) reaction without altering the morphology. During this process, Pb²⁺ ions exhibited a tendency to selectively undergo cation exchange with the wurtzite (WZ) structure of ZnSe, likely due to the preference of larger Pb²⁺ ions to occupy interstitial sites with relatively larger interplanar distances in WZ rather than ZB. Another cation exchange reaction was conducted using Cu⁺ ions instead of Pb²⁺ ions. Due to thermodynamic factors such as the superior stability of the complex formed by Zn ions and oleate and the high bond dissociation energy of PbSe, making it less favorable for cation exchange with Cu⁺ ions, the ZB portion of ZnSe selectively undergoes cation exchange with Cu⁺ions, leading to its transformation into Cu₂Se. Furthermore, the structural similarity between the antifluorite phase of Cu₂Se and the ZB phase of ZnSe allows for a more rational kickout mechanism during the cation exchange process, lowering the CE process's activation energy. <br/>To conclude, we successfully synthesized kink-structured Cu₂Se-PbSe superlattice nanowires. The kinked structure and superlattice act as highly effective phonon scattering centers, reducing thermal conductivity. Furthermore, we were able to partially dope PbSe with Cu⁺ ions. The dense phase boundary between PbSe and Cu₂Se can alleviate lattice distortion in PbSe during the cation exchange process, facilitating the simultaneous provision of Cu_i and Cu_Pb. This enables higher Cu doping concentrations, leading to increased electrical conductivity and, consequently, a higher power factor. Overall, an enhancement of figure of merit (<i>ZT</i>) was observed in the kinked Cu₂Se-PbSe nanowires