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Flowing water can be used as an energy source for generators, providing a major part of the energy for daily life. However, water is rarely used for information or electronic devices. Herein, we present the feasibility of a polarized liquid-triggered photodetector in which polarized water is sandwiched between graphene and a semiconductor. Due to the polarization and depolarization processes of water molecules driven by photogenerated carriers, a photo-sensitive current can be repeatedly produced, resulting in a high-performance photodetector. The response wavelength of the photodetector can be fine-tuned as a result of the free choice of semiconductors as there is no requirement of lattice match between graphene and the semiconductors. Under zero voltage bias, the responsivity and specific detectivity of Gr/NaCl (0.5 M)W/N-GaN reach values of 130.7 mA/W and 2.3 × 109 Jones under 350 nm illumination, respectively. Meanwhile, using a polar liquid photodetector can successfully read the photoplethysmography signals to produce accurate oxygen blood saturation and heart rate. Compared with the commercial pulse oximetry sensor, the average errors of oxygen saturation and heart rate in the designed photoplethysmography sensor are ~1.9% and ~2.1%, respectively. This study reveals that water can be used as a high-performance photodetector in informative industries.

The excitation, rebound, and transport process of hot carriers (HCs) inside dynamic diode (DD) based on insulators has been rarely explored due to the original stereotyped in which it was thought that the insulators are nonconductive. However, the carrier dynamics of DD is totally different from the static diode, which may bring a subverting insight of insulators. Herein, we discovered insulators could be conductive under the framework of DD; the HC process inside the rebounding procedure caused by the disappearance and reestablishment of the built-in electric field at the interface of insulator/semiconductor heterostructure is the main generation mechanism. This type of DD can response fast up to 1 μs to mechanical excitation with an output of ~10 V, showing a wide band frequency response under different input frequencies from 0 to 40 kHz. It can work under extreme environments; various applications like underwater communication network, self-powered sensor/detector in the sea environment, and life health monitoring can be achieved.

There is a rising prospective in harvesting energy from the environment, as in situ energy is required for the distributed sensors in the interconnected information society, among which the water flow energy is the most potential candidate as a clean and abundant mechanical source. However, for microscale and unordered movement of water, achieving a sustainable direct-current generating device with high output to drive the load element is still challenging, which requires for further exploration. Herein, we propose a dynamic PN water junction generator with moving water sandwiched between two semiconductors, which outputs a sustainable direct-current voltage of 0.3 V and a current of 0.64 μA. The mechanism can be attributed to the dynamic polarization process of water as moving dielectric medium in the dynamic PN water junction, under the Fermi level difference of two semiconductors. We further demonstrate an encapsulated portable power-generating device with simple structure and continuous direct-current voltage output of 0.11 V, which exhibits its promising potential application in the field of wearable devices and the IoTs.

Recharging the batteries by wireless energy facilitates the long-term running of the batteries, which will save numerous works of battery maintenance and replacement. Thus, harvesting energy form radio frequency (RF) waves has become the most promising solution for providing the micropower needed for wireless sensor applications, especially in a widely distributed 4G/5G wireless network. However, the current research on rectenna is mainly focused on the integrated antenna coupled with metal-insulator-metal tunneling diodes. Herein, by adopting the plasmon excitation of graphene and quantum tunneling process between graphene and GaAs or GaN, we demonstrated the feasibility of harvesting energy from the 915 MHz wireless source belonging to 5G in the FR1 range (450 MHz–6 GHz) which is also known as sub-6G. The generated current and voltage can be observed continuously, with the direction defined by the built-in field between graphene and GaAs and the incident electromagnetic waves treated as the quantum energy source. Under the RF illumination, the generated current increases rapidly and the value can reach in the order of 10-8–10-7 A. The harvester can work under the multiple channel mode, harvesting energy simultaneously from different flows of wireless energy in the air. This research will open a new avenue for wireless harvesting by using the ultrafast process of quantum tunneling and unique physical properties of graphene.

Searching for light and miniaturized functional device structures for sustainable energy gathering from the environment is the focus of energy society with the development of the internet of things. The proposal of a dynamic heterojunction-based direct current generator builds up new platforms for developing in situ energy. However, the requirement of different semiconductors in dynamic heterojunction is too complex to wide applications, generating energy loss for crystal structure mismatch. Herein, dynamic homojunction generators are explored, with the same semiconductor and majority carrier type. Systematic experiments reveal that the majority of carrier directional separation originates from the breaking symmetry between carrier distribution, leading to the rebounding effect of carriers by the interfacial electric field. Strikingly, NN Si homojunction with different Fermi levels can also output the electricity with higher current density than PP/PN homojunction, attributing to higher carrier mobility. The current density is as high as 214.0 A/m2, and internal impedance is as low as 3.6 kΩ, matching well with the impedance of electron components. Furthermore, the N-i-N structure is explored, whose output voltage can be further improved to 1.3 V in the case of the N-Si/Al2O3/N-Si structure, attributing to the enhanced interfacial barrier. This approach provides a simple and feasible way of converting low-frequency disordered mechanical motion into electricity.

Static heterojunction-based electronic devices have been widely applied because carrier dynamic processes between semiconductors can be designed through band gap engineering. Herein, we demonstrate a tunable direct-current generator based on the dynamic heterojunction, whose mechanism is based on breaking the symmetry of drift and diffusion currents and rebounding hot carrier transport in dynamic heterojunctions. Furthermore, the output voltage can be delicately adjusted and enhanced with the interface energy level engineering of inserting dielectric layers. Under the ultrahigh interface electric field, hot electrons will still transfer across the interface through the tunneling and hopping effect. In particular, the intrinsic anisotropy of black phosphorus arising from the lattice structure produces extraordinary electronic, transport, and mechanical properties exploited in our dynamic heterojunction generator. Herein, the voltage of 6.1 V, current density of 124.0 A/m2, power density of 201.0 W/m2, and energy-conversion efficiency of 31.4% have been achieved based on the dynamic black phosphorus/AlN/Si heterojunction, which can be used to directly and synchronously light up light-emitting diodes. This direct-current generator has the potential to convert ubiquitous mechanical energy into electric energy and is a promising candidate for novel portable and miniaturized power sources in the in situ energy acquisition field.