Enhanced Thermoelectric Performance and Stability of 2D Sn-Based Perovskite—Choice of Spacer and Doping Strategy

Hybrid halide perovskites are gaining increasing attention for their ultra-low thermal conductivity, making them highly promising thermoelectric materials. Since the thermoelectric figure of merit (<i>ZT</i>), which evaluates device thermoelectric efficiency, is determined by thermal conductivity (<i>κ</i>), Seebeck coefficient (<i>S</i>), electrical conductivity (<i>σ</i>), and temperature at the same time, the resulting <i>ZT</i> represents a compromise between these values. In addition to low <i>κ</i>, perovskite materials have<i> </i>excellent composition tunability and great potential for achieving higher <i>ZT</i>. However, while researchers have made great efforts to improve the thermoelectric performance of perovskites, their thermoelectric performance is still limited by the low electrical conductivity and poor stability upon exposure to ambient air (moisture and oxygen). In this work, we focused on Sn-based halide perovskite for its remarkably higher <i>σ </i>than Pb-based perovskite. Based on previously published two-dimensional (2D) PEA₂SnX₄ perovskites (PEA denotes phenethylammonium, X for halide) as a thermoelectric material, we investigated different 2D Sn-based perovskite materials to identify compositions leading to good performance. As all halide perovskites have low thermal conductivity, we focused on investigating the effects of composition on electrical conductivity and stability. Both bromide or iodide-based perovskites with both Ruddlesden Popper (RP) and Dion-Jacobson (DJ) spacers were studied in this work, among which TEA₂SnI₄ perovskite was outstanding for its higher <i>σ</i> and S compared to PEA₂SnI₄ and best ambient stability (TEA stands for 2-thiopheneethylammonium). Moreover, different dopants were applied to PEA₂SnI₄and TEA₂SnI₄ for higher <i>σ</i>, among which F4TCNQ and SnI₄ were found to be effective in increasing conductivity.