Droplet-based electricity generators are lightweight and nearly metal-free, making them promising for hydraulic power applications. However, two critical challenges hinder their practical application: significant performance degradation, potentially up to 90%, in existing small-scale integrated panels, and low efficiency, often less than 2%, in storing the irregular high-voltage pulsed electricity produced by large-scale arrays. Here, we demonstrate that by tailoring the bottom electrodes so that their area is comparable to the spread area of the impinging water droplets, we double the average output power of individual cells and fabricate large-scale (30-cell) arrays that achieve approximately 2.5 times higher power than state-of-the-art arrays. Furthermore, without using any power management chip, we integrate a large-scale (400-cell) micro-supercapacitor array to store the irregular high-voltage electricity produced by the 30-cell generator array at an efficiency of 21.8%. The integration of large-scale electricity generator arrays and micro-supercapacitor arrays forms a simple, chipless, self-charging power system with an output power of 81.2 μW, which is 27 times higher than current systems based on 30-cell arrays. This work provides important insights towards practical applications of droplet-based electricity generators.

In vitro models have now become a realistic alternative to animal models for cardiotoxicity assessment. However, the cost and expertise required to implement in vitro electrophysiology systems to study cardiac cells pose a strong obstacle to their widespread use. This study presents a cost-effective approach forin vitro cardiac electrophysiology using fully printed graphene-based microelectrode arrays (pGMEAs) coupled to an open-source signal acquisition system. We characterized the pGMEAs' electrical properties and biocompatibility, observing low impedance values and cell viability. We demonstrated the platform's capability to record spontaneous electrophysiological activity from HL-1 cell cultures, and we monitored and quantified their responses to chemical stimulation with noradrenaline. This study demonstrates the feasibility of producing fully printed graphene-based devices for in vitro electrophysiology. The accessible and versatile platform we present here represents a step further in the development of alternative methods for cardiac safety screening.

Organic electrochemical transistors (OECTs) are key bioelectronic devices with applications in neuromorphics, sensing, and flexible electronics. OECTs made using biobased and biodegradable materials are emerging as a sustainable alternative to nondegradable plastic and metal-based electronics. Printing is the key technique used to fabricate these types of devices, enabling fabrication at room temperature and using benign solvents, such as water. However, printing techniques suffer from relatively low resolution (tens to hundreds of micrometers), far below the micrometer resolution achieved via conventional metal deposition and photolithography. Here, we present a high-throughput additive-subtractive microfabrication strategy for carbon-based flexible OECTs using biodegradable materials and room-temperature processing. Additive manufacturing of large features is achieved via extrusion printing of a graphene ink to fabricate electrode contacts on cellulose acetate (CA), which serves both as the substrate and as the insulation layer. Combined with femtosecond (fs) laser ablation, this approach enables micrometer-resolution patterning of freestanding OECTs with channel openings down to 1 μm and sheet resistance below 10 Ω/sq. By tuning laser parameters, we demonstrate both selective and simultaneous ablation strategies, enabling the fabrication of horizontal, vertical, and planar-gated OECTs, as well as complementary NOT gate inverters. Thermal degradation studies in air show that over 80% of the device mass decomposes below 360 °C, providing a low-energy route for device disposal and addressing the environmental impact of electronic waste. This approach offers a lithography-free pathway toward the rapid prototyping of high-resolution, sustainable organic electronics, combining circularity, process simplicity, and architectural versatility for next-generation bioelectronic applications. 

Self-charging power systems (SCPSs) are envisioned as promising solutions for emerging electronics to mitigate the increasing global concern about battery waste. However, present SCPSs suffer from large form factors, unscalable fabrication, and material complexity. Herein, a type of highly stable, eco-friendly conductive inks based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are developed for direct ink writing of multiple components in the SCPSs, including electrodes for miniaturized spacer-free triboelectric nanogenerators (TENGs) and microsupercapacitors (MSCs), and interconnects. The principle of “one ink, multiple functions” enables to almost fully print the entire SCPSs on the same paper substrate in a monolithic manner without post-integration. The monolithic fabrication significantly improves the upscaling capability for manufacturing and reduces the form factor of the entire SCPSs (a small footprint area of ≈2 cm × 3 cm and thickness of ≈1 mm). After pressing/releasing the TENGs for ≈79000 cycles, the 3-cell series-connected MSC array can be charged to 1.6 V while the 6-cell array to 3.0 V. On-paper SCPSs are promising to serve as lightweight, thin, sustainable, and low-cost power supplies. 

The rapid development of emerging electronics requires power sources with the advantages of lightweight, high efficiency, and portability. Considering the use of critical raw materials (such as Li, Co, etc.) and the increasing global concern of battery waste, self-charging power systems (SCPSs) integrating energy harvesting, power management, and energy storage devices have been envisioned as promising solutions to replace traditional batteries to avoid the use of toxic materials and the need of frequent recharging/replacement. Up to date, the reported SCPSs still hold the problem of large form factor, unscalable fabrication, noble materials, and material complexity. In our work, a highly stable and eco-friendly organic conductive ink based on poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) has been developed for monolithic fabrication on-paper SCPSs almost fully through a simple direct ink writing (DIW) process. The ink possesses multiple functions and enables to directly print almost all the key components in the SCPSs, including electrodes for triboelectric nanogenerators (TENGs, mechanical energy harvesters), electrodes for micro-supercapacitors (MSCs, energy storage devices), and interconnects, on the same paper substrate in a monolithic manner without the need for “post-integration”. The monolithic printing process exhibits excellent upscaling capability for manufacturing. In particular, the direct patterning merit of the DIW process offers great flexibility in optimizing the system performance through adjusting the cell number, electrode dimension, and thickness of the MSC arrays. By adjusting the cell numbers, the MSC arrays attain high-rate capability up to 50 V/s to match the pulsing electricity produced from the TENGs. For small-size printed SCPSs (~ 2 cm × 3 cm ×1 mm), after continuous press and release of the TENGs for ~79000 cycles, the 3-cell series-connected MSC array can be charged to 1.6 V while 6-cell array to 3.0 V. For a larger-size printed SCPS with 30 MSC cells (~ 7.5 cm × 5 cm ×0.5 mm), after charging through pressing/releasing for 10 min (nearly 1200 cycles), it can light up a LED (~ 4 W) for 5 s. The demo of successfully powering an LED device exhibited its great potential for powering various electronics. The monolithically fabricated on-paper SCPSs have great potential to serve as lightweight, thin, sustainable, eco-friendly, and low-cost power supplies for emerging electronics.

Harvesting renewable mechanical energy is envisioned as a promising and sustainable way for power generation. Many recent mechanical energy harvesters are able to produce instantaneous (pulsed) electricity with a high peak voltage of over 100 V. However, directly storing such irregular high-voltage pulse electricity remains a great challenge. The use of extra power management components can boost storage efficiency but increase system complexity. Here utilizing the conducting polymer PEDOT:PSS, high-rate metal-free micro-supercapacitor (MSC) arrays are successfully fabricated for direct high-efficiency storage of high-voltage pulse electricity. Within an area of 2.4 × 3.4 cm2 on various paper substrates, large-scale MSC arrays (comprising up to 100 cells) can be printed to deliver a working voltage window of 160 V at an ultrahigh scan rate up to 30 V s−1. The ultrahigh rate capability enables the MSC arrays to quickly capture and efficiently store the high-voltage (≈150 V) pulse electricity produced by a droplet-based electricity generator at a high efficiency of 62%, significantly higher than that (<2%) of the batteries or capacitors demonstrated in the literature. Moreover, the compact and metal-free features make these MSC arrays excellent candidates for sustainable high-performance energy storage in self-charging power systems.