Ionic liquid-enhanced assembly of nanomaterials for highly stable flexible transparent electrodes

Flexible transparent electrodes (FTEs) fabricated from nanomaterials (NMs) are highly valued in portable and wearable electronic devices due to their high transparency, low resistance, flexibility, and formability. Among the various reported methods for preparing FTEs, interfacial self-assembly has gained widespread attention for its simplicity and cost-effectiveness. Moreover, this method allows for effective modulation of nanomaterial structures. However, nanomaterials assembled at the air-water interface are prone to sedimentation due to gravity, leading to lower assembly efficiency and higher material loss. Therefore, developing a high-efficiency, low-loss self-assembly method to achieve stable, large-area flexible transparent electrodes with ordered layered structures remains a significant challenge.

To address this issue, the team led by Lei Jiang from Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, propose an ion liquid-enhanced nanomaterial assembly method to fabricate highly stable, flexible, and transparent electrodes with an ordered layered structure. The use of hydrophobic and non-volatile ionic liquids aids in forming a stable interface with water, effectively preventing the sedimentation of one-dimensional/two-dimensional nanomaterials assembled at the interface. The introduction of ionic liquids plays a crucial role in stabilizing nanomaterial assembly by forming a stable ionic liquid-water interface, significantly reducing nanomaterial loss.

Furthermore, the single-layer nanomaterials prepared via interfacial assembly by Jiang's team exhibit alternating self-climbing behavior, enabling layer-by-layer transfer and the formation of an ordered MXene-coated silver nanowire (AgNW) network film.  This breakthrough enables the efficient, low-loss preparation of large-area AgNW-MXene composite films. The prepared composite films not only demonstrate outstanding optoelectronic properties (sheet resistance of 9.4 Ω sq⁻¹ and transmittance of 93%) but also exhibit prolonged stability due to the effective coverage by MXene. Additionally, compared to traditional indium tin oxide (ITO) films, the prepared AgNW-based composite films display superior flexibility and bending resistance.

Notably, the AgNW-MXene composite films show potential in transparent electromagnetic interference (EMI) shielding and triboelectric nanogenerator (TENG) applications, with an average EMI shielding efficiency (EMI SE) of up to 30.1 dB, surpassing the industry standard requirement of 20 dB. This exceptional performance can be attributed to two key factors. First, the coverage of MXene nanosheets enhances the conductivity of AgNWs, contributing to improved EMI SE. Second, the synergistic effect between the network structure of AgNWs and the two-dimensional layered structure of MXene nanosheets further enhances the internal reflection and absorption of electromagnetic waves, leading to superior EMI SE. Additionally, the composite film can serve as a foundation for assembling TENG devices. A simple hand-patting TENG device can easily drive an electronic watch or timer to function normally. Therefore, this study reveals the immense potential of the fabricated composite films, showcasing their applicability in various flexible optoelectronics applications.