Aqueous-isopropanol-based green ink formulation of single-crystalline transition metal chalcogenides for fully-printed strain-insensitive flexible sensing electronics

The inkjet printing of two-dimensional transition metal chalcogenides (TMDs) holds great promise for the next-generation printed flexible electronics in the context of low-cost and large-scale manufacturing. Notwithstanding the noteworthy advancements witnessed in the formulation of inks and the development of devices, the process of printing high-performance flexible TMD-based electronics remains challenging. This is primarily attributable to the unsatisfactory crystallinity of TMDs and the utilisation of toxic solvents. In this study, we demonstrate the manufacturing process, performance, and applications of fully-printed flexible and multifunctional sensors. We propose the use of a zwitterion cocamidopropyl betaine (CAB) as a dispersant and surfactant to facilitate the liquid-phase exfoliation and uniform dispersion of single-crystalline TMD crystals in water and isopropanol (IPA) for green ink formulation. The absence of additives and binders in the dispersions is a key finding, as it enables the direct production of various TMD inks (i.e., MoS2, MoTe2, WS2, WSe2, and WTe2) with high stability (more than one month) and concentrations (2 mg/mL). The ″green″ ink formulation allows for the uniform deposition of TMD single crystals on flexible substrates, paving the way for strain-insensitive wearable sensing electronics. The study demonstrates that a fully-printed MoSe2/CAB humidity sensor exhibits superior sensitivity (ΔI/I0 = 468.1) and rapid response/recovery times (27 s/0.42 s) under bending deformations. Furthermore, inkjet-printed WTe2/CAB pads on ultrathin substrates (approximately 6 μm) demonstrate exceptional mechanical stability in acquiring high-quality biopotential signals, including electrocardiograph and electromyography. This proposed strategy facilitates the scalable fabrication of TMD-based flexible electronics, thereby significantly advancing their integration into industrial manufacturing processes.

二维过渡金属硫族化合物（two-dimensional transition metal chalcogenides, TMDs）的喷墨印刷技术，在低成本、大规模制造的背景下，对于下一代印刷式柔性电子而言展现出巨大应用前景。尽管在油墨配方研发与器件制备领域已取得显著进展，但制备高性能柔性TMD基电子器件的工艺仍存在诸多挑战。这一困境主要归因于TMDs结晶度欠佳，且当前工艺多使用有毒溶剂。本研究展示了全印刷柔性多功能传感器的制备工艺、性能及应用场景。我们提出采用两性离子椰油酰胺丙基甜菜碱（zwitterion cocamidopropyl betaine, CAB）作为分散剂与表面活性剂，助力单晶TMD晶体在水与异丙醇（isopropanol, IPA）中实现液相剥离与均匀分散，以此制备绿色环保油墨。该分散体系无需额外添加添加剂与粘结剂，这一核心发现可直接制备多种高稳定性（储存时长超1个月）、高浓度（2 mg/mL）的TMD油墨，涵盖二硫化钼（MoS₂）、二碲化钼（MoTe₂）、二硫化钨（WS₂）、二硒化钼（MoSe₂）与二碲化钨（WTe₂）。这种“绿色”油墨配方可实现TMD单晶在柔性基底上的均匀沉积，为抗应变型可穿戴传感电子器件开辟了道路。研究表明，一款全印刷式MoSe₂/CAB湿度传感器在弯曲形变下仍展现出优异的灵敏度（ΔI/I₀ = 468.1）与快速的响应/恢复时间（27 s/0.42 s）。此外，在厚度约6 μm的超薄基底上喷墨印刷的WTe₂/CAB电极垫，在采集包括心电图（electrocardiograph, ECG）与肌电图（electromyography, EMG）在内的高质量生物电位信号时，展现出卓越的机械稳定性。本研究提出的策略可实现TMD基柔性电子器件的规模化制备，从而有力推动其与工业制造流程的深度融合。