Enhanced Piezoelectric Response in Hybrid$_{\, }$Perovskite$_{\, }$via Interfacing with Ferroelectric Pb(Zr,Ti)O$_{3}$

In this work, we have carried out a comprehensive study of the piezoelectric properties of polycrystalline hybrid perovskite CH$_{3}$NH$_{3}$PbI$_{3}$ (MAPbI$_{3})$ thin films on two types of substrates. We spin coated 20-100 nm MAPbI$_{3}$ thin films on gold and ferroelectric Pb(Zr,Ti)O$_{3}$ (PZT), and characterized their piezoelectric coefficient d$_{33}$ using piezoresponse force microscopy (PFM). The MAPbI$_{3}$ thin films on gold showed a d$_{33}$ of \textasciitilde 0.4 pm/V. The epitaxial PZT films (\textasciitilde 50 nm) were deposited on (La,Sr)MnO$_{3}$/SrTiO$_{3}$ substrates, with polarization uniformly oriented in the up direction. For MAPbI$_{3}$ films on PZT, there are regions showing clear PFM phase response, suggesting that MAPbI$_{3}$ is polar with out-of-plane polarization. The PFM amplitude image of MAPbI$_{3}$ indicated the existence of both constructive and destructive piezoresponse with that of PZT. The extracted d$_{33\, }$is$_{\, }$4 pm/V, 10-fold higher than that on gold. The enhanced piezoresponse is attributed to the dipole-dipole interaction between MAPbI$_{3}$ and PZT. Our study points to an effective route to engineer the piezoelectric properties MAPbI$_{3}$ for applications such as mechanical actuators and energy harvesting.