Toward All 2D-Based Printed Raindrop Triboelectric Nanogenerators

The raindrop triboelectric nanogenerator (RD-TENG) is an emerging technology that is designed to harvest energy from raindrops. This application requires materials with a negative triboelectric effect, high surface charge density, mechanical flexibility, and a large surface area, which are key characteristics of 2D materials. However, fundamental research is necessary to understand the potential of 2D materials in this context. This study introduces all-2D-based RD-TENG devices using graphene and transition metal dichalcogenide (TMD) nanosheets. Liquid phase exfoliation (LPE) and liquid cascade centrifugation are used for nanosheet preparation and size selection. The TENGs are fabricated through a rapid, low-cost solution deposition technique based on liquid-liquid interface deposition, which allows screening of different active films and device geometries. Among the tested layered materials, medium-sized molybdenum disulfide (MoS₂) nanosheets (average lateral size≈160 nm, volume-fraction weighted average layer number ≈9) exhibit the highest short-circuit current (µA per drop) and voltage (mV per drop) output due to their most suited electron affinity, capacitance, and surface charge exchange properties. The variations in the performance of the TMD films are further evaluated with X-ray photoelectron spectroscopy (XPS), showing the influence of oxidation differences on charge transfer and charge decay time.