Synergistically Optimizing the Thermoelectric Performance of n-Type SnS through an Integrated Systematic Approach

Tin(II) sulfide (SnS) is a promising p-type semiconductor known for its high thermoelectric performance and eco-friendly properties, offering a viable alternative to group IV-VI compounds. However, achieving n-type conductivity in SnS has been challenging due to the propensity for native Sn vacancies. This study addresses this challenge by synthesizing polycrystalline n-type SnS_1-δ (δ = 0.05 and 0.075) samples through solid-state reaction. By introducing sulfur vacancies to counteract Sn vacancies, followed by aliovalent (Cl^-) and isoelectronic (Se^2-) substitutions, we significantly enhance the thermoelectric performance of n-type SnS. Chlorine doping further improves electrical conductivity, with SnS_0.455Se_0.45Cl_0.02 showing superior performance. Additionally, incorporating 0.03 mol % SnCl₂ in SnS_0.475Se_0.45 compensates for intrinsic Sn vacancies, optimizing the power factor and lowering lattice thermal conductivity. Consequently, we realized a figure of merit ZT (ZT_max) of ≈0.7 at 823 K and an average ZT (ZT_ave) of ≈0.2 from 308 to 823 K, the highest reported values for n-type SnS. This work advances the optimization of n-type SnS and lays the groundwork for developing SnS-based thermoelectric devices.