Can Pressure be a Good Strategy for Optimizing Thermoelectric Performance of SnPS₃?

External pressure can significantly alter the transport coefficients, power factor, and figure of merit because of its direct influence on the electronic structure, electron–phonon, and phonon–phonon couplings. This study delves into the electronic and thermal transport properties of (Formula presented.) at external pressures up to 30 GPa using first-principles calculations and Boltzmann transport theory. The electron–phonon relaxation time is computed within the electron–phonon-averaged (EPA) approximation, enabling exploration beyond the constant relaxation time approximation. The first-principles calculations reveal an indirect bandgap of 1.76 (without pressure) and 0.12 eV (30 GPa). The density functional perturbation theory calculations confirm the dynamic stability of (Formula presented.) at external pressure up to 30 GPa. The electronic transport properties are improved by more than one order of magnitude at 30 GPa, consistent with experimental observations. The Peierls–Boltzmann transport calculations demonstrate the room temperature lattice thermal conductivity of 0.22 (without pressure) and 7.4 (Formula presented.) (at 30 GPa). The results emanate that (Formula presented.) exhibits (Formula presented.) of 0.71 at 900 K at a hole doping of 2 (Formula presented.) (Formula presented.) at zero pressure, which decreases with increasing pressure. The findings explore the effect of external pressure on both electronic and thermal transport properties of (Formula presented.), warranting further experimental exploration of thermal transport properties at higher pressures.