First-Principles Investigation of the Effects of B-Type Medium Entropy Local Sublattice on the Physical Properties of ABX3 (A = K, Ag, Cu; B = SixGeySnzPb(1−x−y−z); X = Br, I) Metal Halide Perovskites

The stability, elasticity, and thermoelectric property of ABX3 (A = K, Ag, Cu; B = SixGeySnzPb(1−x−y−z); X = Br, I) metal halide perovskites (MHPs) with B-type medium entropy sub-lattices (MESLs) are investigated by first principles calculations. The results show that the order of dissociation formation enthalpy ΔHf for conventional unit cell APbX3 with changing atomic type in the A site is K < Ag < Cu, and for each case Br < I. The ΔHf values of (KBBr3, KBI3, AgBBr3) and (CuBBr3, CuBI3, AgBI3) with MESL in the B site slightly increase and decrease, respectively, with the exception of certain situations. By using Slack’s model, the lattice thermal conductivity (LTC) κl at finite temperatures is obtained. It is found that the LTC κl for all MHPs shows an extremely low value at room temperature, not exceeding 1.5 Wm−1K−1. Interestingly, it is also found that the B-type MESLs significantly increase the ZTmax values of KPbX3, whereas they decrease the ZTmax values of CuPbX3 and AgPbX3, except for in some cases. All calculated parameters show obvious variation laws with the increase in atomic number of the high-content B-type atom in the ABX3, and CuBX3 and AgBX3 materials exhibit an extremely low ZT value (ZT ≈ 0) due to their high σ accompanied by high κe and low S. We believe that KSi0.375Ge0.25Sn0.25Pb0.125Br3 with a ZT value of 3.012 can serve as an excellent thermoelectric material at room temperature. These findings make contributions to the design of high-quality thermoelectric MHP materials.