# Toward All 2D‐Based Printed Raindrop Triboelectric Nanogenerators

## TL;DR

Researchers developed a raindrop energy harvester using 2D materials like graphene and MoS2, which can generate electricity from falling raindrops.

## Contribution

The study introduces all-2D-based RD-TENG devices fabricated via a low-cost solution deposition technique for scalable material screening.

## Key findings

- MoS2 nanosheets with specific size and layer number showed the highest output in short-circuit current and voltage per raindrop.
- XPS analysis revealed oxidation differences affect charge transfer and decay time in TMD films.
- Liquid-liquid interface deposition enables rapid and uniform assembly of nanosheet films for device fabrication.

## Abstract

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.

A raindrop triboelectric nanogenerator (RD‐TENG) based on solution‐deposited 2D materials is described, where successive drop impacts generate short‐circuit signals. Graphene–SWCNT hybrid films serve as conductive contacts and transition metal dichalcogenides as active layer. Liquid–liquid interface deposition enables rapid and uniform assembly of nanosheet films, offering a scalable platform for systematic material screening in future RD‐TENG designs.