Tailoring the transport coefficients and thermoelectric properties of Cs2NaYbCl6 perovskite by doping and nanoengineering: A first-principles based theoretical approach

We present a first-principles investigation of the combined effects of chemical doping and nanostructuring on the thermoelectric performance of the double halide perovskite Cs2NaYbCl6. Using density functional theory and Boltzmann transport calculations, we explicitly include all relevant scattering mechanisms (namely, electron–phonon, phonon–phonon, Coulomb impurity, phonon–impurity, and grain boundary scattering) to evaluate electrical and thermal transport coefficients. Our results show that Coulomb scattering from dopants is strongly screened and negligible compared to dominant electron–phonon interactions. Thus, both n- and p-type doping enhance electrical conductivity while only moderately reducing the Seebeck coefficient, leading to a significant increase in power factor. Phonon–impurity scattering is found to be minimal, while grain boundary scattering effectively reduces lattice thermal conductivity without strongly affecting carrier mobility. Combining optimal n-type doping (1019cm−3) with nanoscale grains (10 nm), the figure of merit ZT increases from ∼10−8 in the pristine crystal to ∼0.12. These findings demonstrate a viable pathway for improving thermoelectric efficiency in wide-band-gap, lead-free perovskites through controlled extrinsic modifications.