  We report a more than 10-fold enhancement of the piezoelectric coefficient
$d_{33}$ of polycrystalline CH$_3$NH$_3$PbI$_3$ (MAPbI$_3$) films when
interfacing them with ferroelectric PbZr$_{0.2}$Ti$_{0.8}$O$_3$ (PZT).
Piezo-response force microscopy (PFM) studies reveal $d_{33}^{MAPbI_3}$ values
of ~0.3 pm/V for MAPbI$_3$ deposited on Au and ITO surfaces, with small phase
angles fluctuating at length scales smaller than the grain size. In sharp
contrast, on samples prepared on epitaxial PZT films, we observe large scale
polar domains exhibiting clear, close to 90{\deg} PFM phase angles, pointing to
polar axes along the film normal. By separating the contributions from the
MAPbI$_3$ and PZT layers, we extract a significantly enhanced
$d_{33}^{MAPbI_3}$ value of ~4 pm/V, which is attributed to the long-range
dipole-dipole interaction facilitated domain nucleation. We also discuss the
effect of the interfacial screening layer on the preferred polar direction.
