Organic piezosensitive charge-transfer complexes with crystal-to-crystal phase transition for flexible energy harvesting

Abstract

Organic piezosensitive materials with high efficiency are in high demand because of their great potential for low temperature, solution-processed and low-cost energy harvesting, mechanical sensing and biomedical applications. Here, we synthesized a new mechanically sensitive charge-transfer (CT) complex consisting of a mixed-stacked dibenzocarbazole analog (DBCz) and a tetracyanodiazafluorene analog (TCAF) in a cocrystallization manner, called DTC for short. The as-prepared, thermodynamically stable α-DTC complex could undergo a reversible crystal-to-crystal transition through the molecular displacement and rotation under heat or mechanical stimuli. The force-triggered structural change enabled fine band structure modulation, confirmed from density functional theory (DFT) calculations. In addition, we successfully constructed triboelectric energy harvesting devices, using bar-coated α-DTC/multilayer graphene/polydimethylsiloxane (PDMS) hybrid films, which displayed excellent output performance with an open-circuit voltage of up to 60 V and a short-circuit current density of 0.67 μA cm⁻². Such a single-electrode nanogenerator can work as multifunctional e-skin to achieve good responses to various external mechanical forces for information transmission. We believe that the discovery of this new family of organic piezosensitive materials, charge-transfer complexes, has great potential in flexible, wearable, and self-powered electronics.