Toward In Vivo Energy Harvesters: High Piezoelectric Response in a Pharmaceutical Drug Polymorph Enabled by Monopolar Domain Architecture

ABSTRACT

Biocompatible piezoelectric materials capable of efficient mechanical‐to‐electrical energy conversion are critical for the development of implantable energy harvesters and in vivo biomedical sensors. Here, we report an unusually high piezoelectric response in a polymorph of the pharmaceutical drug hydrochlorothiazide (HCT), originating from conformationally driven solid‐state chirality and an uncommon monopolar domain architecture. In contrast to most polar molecular crystals, where micro‐ to nanoscale orientational disorder suppresses macroscopic polarization, HCT forms enantiomorphic twin domains arranged in a tail‐to‐tail polarity configuration. This intrinsic domain organization eliminates the need for external electric poling during device fabrication, providing a significant technological advantage for biocompatible applications. Kelvin probe force microscopy (KPFM) surface potential mapping and piezoresponse force microscopy (PFM) phase contrast measurements provide compelling experimental support for this polarity model. X‐ray quantum crystallography reveals an enhanced spontaneous polarization of 10.2 µC cm ⁻² , while facet‐resolved PFM measurements yield an effective piezoelectric coefficient of ∼9.2 ± 0.13 pm V ⁻¹ . Enabled by the monopolar domain architecture, the fabricated devices generate a remarkably high piezoelectric voltage output of 88 ± 5.2 V under moderate mechanical loading (29–30 N), placing it among the highest voltage outputs reported to date for an organic material‐based energy harvesting device.