Thermal conductivity and diffusivity of triple-cation perovskite halide materials for solar cells.

We report on the measurement of thermal conductivity and thermal diffusivity by a modulated thermoreflectance microscopy technique on a mixed-cation perovskite material [Cs_0.05(formamidinium_0.83methylammonium_0.17)_0.95Pb(I_0.83Br_0.17)₃] widely applied for solution-processed perovskite solar cells. Such materials are supposed to present improved thermal stability compared to methylammonium-based single cation perovskites. Our measurements are performed on perovskite/TiO₂/SnO₂:F/SiO₂ structures, with perovskite thicknesses ranging between 250 nm and 1000 nm. This configuration is the one of a real solar cell, with the same substrate and intermediate layers as of an operating device. We measured a thermal conductivity k_per of 0.26 ± 0.03 W m⁻¹ K⁻¹ and a thermal diffusivity D_per of 3.5 × 10⁻⁷ ± 0.5 m² s⁻¹. The value for thermal conductivity is comparable to the one measured on single cation perovskites, which is generally in the 0.2–0.6 range. The value for thermal diffusivity has not been reported previously. [ABSTRACT FROM AUTHOR]