Enhanced Piezoelectric Response in Hybrid Lead Halide Perovskite Thin Films via Interfacing with Ferroelectric PbZr0.2Ti0.8O3

We report a more than 10-fold enhancement of the piezoelectric coefficient d 33 of polycrystalline CH3NH3PbI3 (MAPbI(3)) films when interfacing them with ferroelectric PbZr0.2Ti0.8O3 (PZT). Piezoresponse force microscopy (PFM) studies reveal d(33)(MAPbI)3 values of 0.3-0.4 pm/V for MAPbI(3) deposited on Au, indium tin oxide, and SrTiO3 surfaces, with small phase angle 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 180 degrees PFM phase contrasts, pointing to polar axes along the film normal. By separating the piezoresponse contributions from the MAPbI(3) and PZT layers, we extract a significantly higher d(33)(MAPbI)3 of similar to 4 pm/V, which is attributed to the enhanced alignment of the MA molecular dipoles promoted by the unbalanced surface potential of PZT. We also discuss the effect of the interfacial screening layer on the preferred polar direction.