Investigation of ferroelectric and piezoelectric properties of hybrid halide perovskite (HHP) thin films for the Internet of Things (IoT) applications

Abstract

This thesis presents a systematic investigation of the ferroelectric and piezoelectric properties of layered hybrid halide perovskite (HHP) thin films to integrate the corresponding piezoelectric devices for self-powered Internet of Things (IoT) systems. Initial efforts focused on the optimization of layered halide perovskite of (BA)₂MA_n-1Pb_nBr_3n+1 (n = 1 and 2) thin films fabricated in a metal/semiconductor/metal (M/S/M) ferroelectric device architecture, emphasizing its importance for integration with electronic devices. This investigation revealed the importance of additional barrier layers (PCBM and Cr/Cr₂O₃) for improving ferroelectric properties. This study further identifies the challenges in achieving phase pure (BA)₂FA_n-1Pb_nBr_3n+1 (n = 2 to 5) and (PEA)₂MA_n-1Pb_nBr_3n+1 (n = 1 to 4) HHP thin films deposited with blade coating technique under ambient conditions. The phase purity and polar properties were confirmed through X-ray diffraction, differential scanning calorimetry, UV-Visible, and Raman spectroscopy.

The piezoelectric energy-harvesting capabilities of (BA)₂FA_n-1Pb_nBr_3n+1 (n = 2 to 5) HHP thin films were systematically evaluated under human biological motion and dynamic linear forces. The piezoelectric power output of the (BA)₂FAPb₂Br₇ device improved by ~1.8× after PCBM‑based surface passivation. Additionally, light-induced and pyro-enhanced piezoelectric responses were identified in (BA)₂FA_n-1Pb_nBr_3n+1 (n = 2 to 5) thin films. The ferroelectric switchable polarisation in HHP thin films was confirmed using PUND analysis. The ferroelectric behaviour of aromatic spacer (PEA)₂MA_n-1Pb_nBr_3n+1 (n = 1 to 4) HHP thin films was examined as a function of processing temperatures. Room-temperature-processed (PEA)₂MA_n-1Pb_nBr_3n+1 (n = 2) thin films demonstrated the highest saturation polarization of 9.8 µC cm⁻² at 1 Hz, along with a pyroelectric coefficient of 1.7 µC m⁻² K⁻¹.

Overall, this thesis work reveals that the ferroelectric, pyroelectric, and piezoelectric properties of these layered HHP thin films are fundamentally determined by the choice of spacer (A’) and small A cation (BA, MA, FA, and PEA) and the number of inorganic layers (n).

Date of Award	1 Dec 2026
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Lethy Krishnan Jagadamma (Supervisor)