Photoferroelectric and Photopiezoelectric Properties of Organometal Halide Perovskites.

Piezoelectrics play a critical role in various applications. The permanent dipole associated with the molecular cations in organometal halide perovskites (OMHPs) may lead to spontaneous polarization and thus piezoelectricity. Here we explore the piezoelectric properties of OMHPs with density functional theory. We find that the piezoelectric coefficient depends sensitively on the molecular ordering and that the experimentally observed light-enhanced piezoelectricity is likely due to a nonpolar to polar structural transition. By comparing OMHPs with different atomic substitutions in the ABX3 architecture, we find that the displacement of the B-site cation contributes to nearly all of the piezoelectric response and that the competition between A-X hydrogen bond and B-X metal-halide bond in OMHPs controls the piezoelectric properties. These results highlight the potential of the OMHP architecture for designing new functional photoferroelectrics and photopiezoelectrics.