Effects of substitutional doping CsSn0.75A0.25I3 (A=B, Sb) in the thermoelectric properties of the B-γ phase from first principles

Abstract

Among hybrid and all-inorganic halide perovskites, CsSnI3 has stood out with moderate electrical conductivity and ultralow thermal conductivity. Nevertheless, the former is still low compared to values of traditional thermoelectric materials, this makes its applications scarce. Herein, we wish to present a DFT study combined with the application of the Boltzmann transport equation, to determine the effects of p and n-type substitutional doping in the lattice structure, electronic and thermoelectric properties of CsSn0.75A025I3 (A = B, Sb). Our calculations show that doping increases the thermoelectric power factor to 181.2 µW m−1 K−2 under Sb-doping, which represents a twofold value compared to 78.3 µW m−1 K−2 of the pristine lattice; under B-doping we obtained a value of 145.6 µW m−1 K−2. CsSnI3 has higher power factor upon n-type doping. Finally, yet importantly, we further examine the shifts in the Fermi level using the effective mass model framework. In doing so, our work predicts a performance enhancement by achieving a Fermi energy level close to the VBM, or CBM. Similarly, our work demonstrates that doping represents an effective way to improve the thermoelectric power factor of CsSnI3, this being attributed to the increase of charge carriers and the modification of the band structure.