Polar Organic Charge-Transfer Complex of the Asymmetrical Component for Flexible Piezoelectric Energy Harvesting and Self-Powered Wearable Sensors

Abstract

Organic piezomaterials have attracted much attention because of their easy processing, lightweight, and mechanic flexibility properties. Developing new smart organic piezomaterials is highly required for new-generation electronic applications. Here, we found a novel organic piezomaterial of organic charge-transfer complex (CTC) consisting of dibenzcarbazole analogue (DBCz) and tetracyanoquinodimethane (TCNQ) in the molecular-level heterojunction stacking mode. The DBCz−TCNQ complex exhibited ferroelectric properties (the saturated polarization of ∼1.23 μC/cm 2 ) at room temperature with a low coercive field. The noncentrosymmetric alignment (Pc space group) led to a spontaneous polarization of this architecture and thus was the origin of the piezoelectric behavior. Lateral piezoelectric nanogenerators (PENGs) based on the thermal evaporated CTC thin-film exhibited significant energy conversion behavior under mechanical agitation with a calculated piezoelectric coefficient (d 31 ) of ∼33 pC/N. Furthermore, such a binary CTC thin-film constructed single-electrode PENG could show steady-state sensing performance to external stimuli as this flexible wearable device precisely detected physiological signals (e.g., finger bending, blink movement, carotid artery, etc.) with a self-powered supply. This work provides that the polar CTCs can act as efficient piezomaterials for flexible energy harvesting, conversion, and wearable sensing devices with a self-powered supply, enabling great potential in healthcare, motion detection, human−machine interfaces, etc.

Homochirality-Induced Piezoelectricity in a Single-Component Molecular System

“…Piezoelectricity has been extensively explored with inorganic ceramic oxides owing to their excellent piezoresponse. , However, the presence of rare-earth and other heavy metal ions in ceramic-based nanogenerator devices often leads to brittleness (low fracture toughness), high stiffness, high density, and the necessity for elevated processing temperatures in the solid-state sintering process. , Moreover, the presence of toxic metal ions such as Pb(II) in ceramic materials hinders their use in flexible energy harvesting and wearable electronic applications. , Recently, significant developments have been made in single-component molecular metal-free piezoelectric crystals and their utilization in nanogenerator applications . Notable examples of single-component systems include molecules such as N , N ′-bis(4-nitrophenyl)methanediamine (BPNA), dibenzcarbazole-tetracyanoquinodimethane (DBCz–TCNQ), trimethylamine borane (TMAB), and oligopeptides such as Pro-Phe-Phe, which were shown to exhibit piezoelectricity either in their crystalline state or in the form of their polymer composites. However, piezoelectric crystals require the absence of inversion symmetry, and despite the fact that 20-point groups among the 32 crystallographic classes are acentric, there is a strong tendency of matter to crystallize in centrosymmetric settings. , Therefore, the preparation of noncentrosymmetric solids from achiral components is often a trial-and-error effort, making it a laborious task.…”