Thermoelectric Performance of Two-Dimensional Halide Perovskites Featuring Conjugated Ligands

Sn-based halide perovskites are promising for thermoelectric (TE) device application because of their high electrical conductivity and their low thermal conductivity. However, conventional three-dimensional Sn-based perovskite are not stable under typical TE device operating conditions. Reducing the dimensionality of Sn-based perovskite improves both the environmental stability and the TE performance by reducing the thermal conductivity. Here, we demonstrate the carrier concentration and temperature dependence of Seebeck coefficients and electrical conductivity of the n = 2 Sn-based 2D perovskites featuring a conjugated ligand, namely (4Tm)₂FASn₂I₇, where 4Tm is 2-(3″′,4′-dimethyl[2,2′:5′,2″:5″,2″′-quaterthiophen]-5-yl)ethan-1-ammonium. By doping with 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±3.07 (average) and 7.07 (champion) μW m^-1 K^-2 at 343 K with an electrical conductivity of 5.07 S cm^-1 and Seebeck coefficient of 118.1 μV K^-1. Importantly, these thin films show excellent operational stability (i.e., for over 100 h) at 313 K.