Liquid Metal-Enabled Galvanic Electrocrystallization of Charge-Transfer Complexes

Abstract

Charge-transfer complexes (CTCs), which comprise ordered assemblies of electron acceptor and donor units, represent a mature group of advanced materials. These structures offer unique features, such as intrinsic conductivity, one-dimensional morphology, and tailorable chemistry. To enable the exploitation of CTCs for real-world applications, we investigate CTC nucleation and growth and develop scalable manufacturing methods for their incorporation into electronic systems. In the present work, we combine the unique features of CTCs and liquid metals (LMs) to investigate the galvanic electrocrystallization of tetracyanoquinodimethane complexes with silver (AgTCNQ) and copper (CuTCNQ). The eutectic alloy of gallium and indium (EGaIn) has been shown to be effective in nucleating CTC crystals. EGaIn reduces TCNQ and accumulates metallic precursors at the LM/solution interface via galvanic reduction and stabilization of the metal oxide nanoparticles. This enables the efficient formation and growth of conductive CTC crystals on patterned electronics without the need for an external input. The AgTCNQ wirelike crystals could transfer the autogenous potential of EGaIn, leading to their decoration with Ag nanoparticles. The AgTCNQ crystals grow longer than the CuTCNQ crystals, enabling the interconnection of electronic tracks. This knowledge opens new pathways for scalable CTC crystallization and direct incorporation into electronic systems.

The autogenous potential generated at the interface of gallium (Ga)-based liquid metals is harnessed to trigger galvanic reduction reactions, leading to the formation of metal-tetracyanoquinodimethane charge-transfer complexes (CTCs). This liquid metal interface demonstrated exceptional properties, facilitating the nucleation and growth of CTC crystals.