Thermoelectric Performance of 2D Halide Perovskites Featuring Conjugated Ligands

Sn-based halide perovskites for thermoelectric (TE) device application have begun to receive increased attention due to their innate low thermal conductivity as well as high electrical conductivity. Reducing the dimensionality of perovskite systems can improve the TE performance by reducing the material thermal conductivity. Two-dimensional halide perovskites not only have ultralow thermal conductivity around 0.1 to 0.17 Wm^-1K^-1, but also enhanced environmental stability. Combined with solution processibility and property tunability, 2D perovskites are appealing for next generation TE materials.
In this work, we demonstrate the carrier concentration and temperature dependence of Seebeck coefficients and electrical conductivity of the n=2 Sn-based 2D perovskites featuring conjugated ligand, namely (4Tm)₂FASn₂I₇, where 4Tm is 2-(3″′,4′-dimethyl[2,2′:5′,2″:5″,2″′-quaterthiophen]-5-yl)ethan-1-ammonium. The resulting thin films showed p-type behavior proven by Hall effect and the positive Seebeck coefficients. By intentionally adding SnI₄, we were able to tune the carrier concentration from 2×10¹⁸ to 1.2×10¹⁹ cm^-3 and observed a corresponding trend in TE performance. With optimized doping, (4Tm)₂FASn₂I₇ showed promising power factor of 5.42(average) and 7.07(champion) μWm^-1K^-2 at 343K.