Imagine a scenario where, during a downpour, rainwater not only provides hydration for plants and cleans pollutants from the air but also, through a simple nanostructure device, can collect the energy of raindrops and convert it into electrical energy.

This may sound like a plot from a novel, yet it is not a fictional fantasy but a very likely prospect that could become a reality, prompting us to re-evaluate rainy days. They would no longer be just about the gloomy skies and wet streets but a chance filled with energy opportunities.

Not long ago, Professor Sun Baoquan's team from Soochow University outlined this opportunity in a paper. They invented a new concept of water-voltage power generation device, known as Hydrovoltaic Devices (HDs).

This is a ferroelectric-enhanced water evaporation-induced hydrovoltaic device that can generate a voltage of 1.04V with just a single drop of water. Compared to conventional hydrovoltaic devices, this new device has a significantly improved power generation efficiency.

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In their research, they sandwiched an ultra-thin polarizable ferroelectric polymer (P(VDF-TrFE)) between nanostructured silicon and a top electrode, forming a unique asymmetric heterojunction, thereby creating this hydrovoltaic device.This design enables the device to obtain a robust electrical signal output and provides the electrical signal with excellent adjustability. Under the forward polarization state, a strong asymmetric electric field can be established through the formation of interfacial dipoles, allowing charges to be efficiently swept out of the heterojunction.

Thanks to this mechanism, the open-circuit voltage that the device can produce has been significantly increased to as high as 1.04V, which is almost three times that of the reverse polarization state.

At the same time, this device also has the potential for multifunctional applications. In addition to being used as a power generation device, it also demonstrates excellent environmental sensing characteristics, making it suitable for self-powered environmental temperature detectors, smart water level alarm systems, and automatic/manual dual-mode irrigation control systems.

These applications showcase the unique performance and wide applicability of ferroelectric-assisted hydrovoltaic devices in various fields. Overall, this work has opened up new prospects for ferroelectric-assisted hydrovoltaic devices with adjustable electrical properties and has provided innovative solutions for the development of intelligent and automated systems.

It not only breaks through the flexibility limitations of silicon materials but also provides a completely new path for the development of hydrovoltaic technology. At the same time, this innovative approach will bring new possibilities to energy technology research and provide solutions to the technical challenges in the transition to clean energy.It will provide humans with more options for clean energy, allowing even seemingly insignificant raindrops to inject new vitality into the power system and help humanity better cope with climate change.

In the future, by improving the structure of silicon nanowires, more flexible and adaptable hydrovoltaic devices are expected to be created, thus taking a big step forward in the field of renewable energy.

At present, it is still necessary to optimize the hydrovoltaic power generation devices to meet the needs of more types of environments. Overall, the application prospects of hydrovoltaic power generation devices mainly include the following points:

Firstly, through the integrated development of nanogenerators, the energy of water evaporation, moisture, and heat fluctuations can be collected in conjunction. Mechanical vibrations, solar energy, and wind energy are also potential candidates for this integrated system, that is, it can capture various forms of energy from the surrounding environment.

Secondly, through the integrated development of nanogenerators, not only is it expected to improve the performance of hydrovoltaic power generation, but it can also provide sustainable energy for low-power devices. For the combination of low-power modules such as sensors, memristors, and transistors, hydrovoltaic power generation devices can also become their driving devices.Thirdly, the architecture of the hydrovoltaic power generation device adopts a low-power module combination, which makes it possible for large-scale use in self-powered artificial intelligence, healthcare, and information technology. For example, it can enable skin patches to harvest energy from sweat and moisture, and monitor the user's movement and health status in real time.

Fourthly, as a self-charging system, hydrovoltaic power generation devices have tremendous potential to capture energy from the surrounding environment without an external power source, and can charge energy storage devices.

In the future, by combining hydrovoltaic technology with supercapacitors or batteries, a hybrid self-charging system can be constructed, which is expected to bridge the gap between the current relatively low power generation and actual demand, thereby promoting the development of intelligent communication networks and bringing new prospects for the construction of self-powered high-performance electronic products.

A "World in a Drop of Rain"Currently, in the pursuit of clean power sources, various cutting-edge technologies are continuously opening up new possibilities. For the faint but widely distributed energy, such as the tiny energy in rainwater mentioned earlier, has been studied by Sun Baoquan's research group for several years.

In 2020, they used a silicon nanowire array structure as a power source for hydrovoltaic devices and demonstrated a new type of hydrovoltaic device in a related paper.

This device can utilize the water flow in the silicon nanowire array to generate a constant power supply based on natural water evaporation. It achieves power generation by changing the concentration of ions in the water, as well as changing the length and surface charge of the silicon nanowires. This power generation mechanism is mainly attributed to the streaming potential.

However, due to the complex surface structure of the silicon nanowire array, the recombination of carriers is extremely severe, so it is necessary to selectively control the separation of carriers.

Compared with methods such as surface modification, structural optimization, and photothermal modulation, the method of ferroelectric control has unique advantages in the reversible conversion of field-driven polarization and the long-term maintenance of polarization.A Small Interlayer Brings a Great Electric Field

Later, in the research of this Advanced Energy Materials paper, they found out that adding the ferroelectric material polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) between the active layer and the electrode is a common method to improve the electrical performance of solar cells.

So, by adjusting the polarization direction of the ferroelectric domains, the P(VDF-TrFE) interlayer generates a stronger electric field, which effectively promotes the separation of charge carriers, thereby further increasing the output power.

In the end, the related paper was published in Advanced Energy Materials with the title "Ferroelectric Layer-Assisted Asymmetric Heterojunction Boosts Power Output in Silicon Hydrovoltaic Device"[1].

The first author and co-corresponding author is Song Yuhang, a third-year master's student at Soochow University. Professor Sun Baoquan, Professor Shao Beibei, and Professor Wang Yusheng from Soochow University are the co-corresponding authors.Next, they will continue to focus on silicon nanowire arrays, especially paying close attention to the characteristics of silicon as a rigid material.

Song Yuhang, the first author of this paper, said: "We are well aware of the limitations of silicon in terms of flexibility, and its rigidity may impose certain constraints on the performance of hydrovoltaic devices. Therefore, we plan to start changing the surface morphology of silicon nanowires through the use of etching technology."

Specifically, they will use precise etching processes to treat silicon nanowires directionally, hoping to change the hardness and flexibility of their surface. The aim is to achieve the transfer of silicon nanowire arrays, thus breaking free from the constraints of the rigid parts of silicon, and ultimately obtaining flexible, high-performance silicon nanowire hydrovoltaic devices.