Appealing Perspectives of Hybrid Lead-Iodide Perovskites as Thermoelectric Materials

The fundamental properties of lead halide perovskites, rivaling those of conventional semiconductors, make these systems attractive not just for solar cells but also for a broader playground of energy and nanotechnology applications. The recently measured ultralow thermal conductivity of the perovskites suggests the possibility of high thermoelectric efficiency and the possible use of the perovskites for solar-thermoelectric generation capable to capture both above-gap and below-gap sun illumination. Here we explore this possibility presenting a theoretical analysis of the thermoelectric behavior of CH3NH3PbI3 for a wide range of temperatures and carrier concentrations. For electron doping, we find optimal carrier density n ∼ 1019 cm-3, at which this material displays room-T power factor σS2 ∼ 0.8 × 10-3 W/mK2, derived by moderate electrical conductivity σ and robust thermopower, with Seebeck coefficient S of approximately hundreds of μV/K, typical of polar insulating perovskites. In combination with a measured thermal conductivity ∼0.3-0.5 W/mK, this delivers figure of merits Z ∼ 1-3 × 10-3 K-1, thus in the league of the best performing thermoelectric tellurides and skutterudites. For hole doping, on the other hand, the figure of merit is sensitively reduced by a factor 2 to 3, due to the isotropic nature of the valence band edge. These results can be a stimulus and a guideline to the search of strategies for chemical doping, which has been scarcely investigated so far, for these materials. (Graph Presented).