Strain engineering of metal halide perovskites shows promises for better stability and device performance, but the impact on thermoelectric performance remains elusive. Using the first principles calculations in combination with the Boltzmann transport theory, we investigated the effects of anisotropic strain on electronic structure and carrier transport properties in halide perovskites CsPb(I1-xBrx)3. We demonstrated that the electronic structures and carrier transport properties in CsPb(I1-xBrx)3 can be tailored synergetically through halogen mixing and anisotropic strain effects. Halogen mixing leads to band splitting and anisotropic carrier transport due to symmetry-breaking induced residue strains. Such band splitting reconstructs the band edge and can decrease the carrier effective mass, leading to excellent transport properties. External strains can further push the orbital energies apart from each other in a more controllable manner, surpassing the impact from residue strains. Interestingly, strains can reduce the optimal carrier concentration to achieve the maximum figure of merit (ZT) at 300 K by more than 10 times, providing a new avenue to tackle the longstanding challenge in heavy-doping perovskites. Anisotropic ZT values are very sensitive to the direction and magnitude of strains, showing a wide-ranged variation from 20% to 400% (within ± 2% strains as considered here, with a ZT value up to 1.9) compared to the unstrained cases. This computational work provides strain-engineering strategies to enhance the thermoelectric performance and optimize the doping process in mixed halide perovskites.

Anisotropic srain engineering for tailored carrier transport and thermoelectric performance in mixed halide perovskites CsPb(I1-xBrx)3

ACS Fall 2021

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