Mechanism of In-Plane and Out-of-Plane Tribovoltaic Direct-Current Transport with a Metal/Oxide/Metal Dynamic Heterojunction

Constructing Ultra-High Current Direct-Current Tribo-Photovoltaic Nanogenerators via Cu/Perovskite Schottky Junction

Perovskite-based direct-current triboelectric nanogenerators (DC-TENGs) leveraging the tribo-photovoltaic effect have garnered significant attention for their ability to simultaneously harvest mechanical and solar energy, effectively enhancing the output performance of DC-TENGs. Herein, we innovatively construct a rolling-mode Cu/ternary cation perovskite (FA0.945MA0.025Cs0.03Pb(I0.975Br0.025)3) Schottky junction DC-TENGs with ultrahigh current output and excellent operational stability. The Cu/perovskite Schottky junction ensures the formation of an internal electric field, promoting carrier separation and directional movement for a stable DC output. Under AM 1.5 G illumination, the DC-TENG achieves a short-circuit current (Isc) and current density of 408 μA and 27.2 A/m2, respectively, marking a 119 times increase as compared to dark conditions and the highest reported Isc for perovskite DC-TENGs. With over 30 min of operation, the current output remains stable. The DC-TENGs exhibit promising applications in temperature and humidity sensing and self-powered photodetection. Furthermore, by adjusting the light power density, the optimal internal output impedance of DC-TENGs can be tuned broadly from 0.9 to 132 kΩ, offering great potential for impedance matching in self-powered microelectronic components. This research provides insights into the development of multifunctional DC-TENG devices with coupled mechanical and solar energy, expanding the application scope of perovskite materials and devices.

Evolution of Tribotronics: From Fundamental Concepts to Potential Uses

The intelligent sensing network is one of the key components in the construction of the Internet of Things, and the power supply technology of sensor communication nodes needs to be solved urgently. As a new field combining tribo-potential with semiconductor devices, tribotronics, based on the contact electrification (CE) effect, realizes direct interaction between the external environment and semiconductor devices by combining triboelectric nanogenerator (TENG) and field-effect transistor (FET), further expanding the application prospects of micro/nano energy. In this paper, the research progress of tribotronics is systematically reviewed. Firstly, the mechanism of the CE effect and the working principles of TENG are introduced. Secondly, the regulation theory of tribo-potential on carrier transportation in semiconductor devices and the research status of tribotronic transistors are summarized. Subsequently, the applications of tribotronics in logic circuits and memory devices, smart sensors, and artificial synapses in recent years are demonstrated. Finally, the challenges and development prospects of tribotronics in the future are projected.

MXene Lubricated Tribovoltaic Nanogenerator with High Current Output and Long Lifetime

Tribovoltaic nanogenerators (TVNGs) have the characteristics of high current density, low matched impedance and continuous output, which is expected to solve the problem of power supply for small electronic devices. However, wear occurrence in friction interface will seriously reduce the performance of TVNGs as well as lifetime. Here, we employ MXene solution as lubricate to improve output current density and lifetime of TVNG simultaneously, where a high value of 754 mA m-2 accompanied with a record durability of 90,000 cycles were achieved. By comparing multiple liquid lubricates with different polarity, we show that conductive polar liquid with MXene as additive plays a crucial role in enhancing the electrical output performance and durability of TVNG. Moreover, the universality of MXene solution is well demonstrated in various TVNGs with Cu and P-type Si, and Cu and N-GaAs as material pairs. This work may guide and accelerates the practical application of TVNG in future.

Tribovoltaic Performance of TiO2 Thin Films: Crystallinity, Contact Metal, and Thermoelectric Effects

Tribovoltaic devices are attracting increasing attention as motion-based energy harvesters due to the high local current densities that can be generated. However, while these tribovoltaic devices are being developed, debate remains surrounding their fundamental mechanism. Here, we fabricate thin films from one of the world's most common oxides, TiO₂, and compare the tribovoltaic performance under contact with metals of varying work functions, contact areas, and applied pressure. The resultant current density shows little correlation with the work function of the contact metal and a strong correlation with the contact area. Considering other effects at the metal-semiconductor interface, the thermoelectric coefficients of different metals were calculated, which showed a clear correlation with the tribovoltaic current density. On the microscale, molybdenum showed the highest current density of 192 mA cm^-2. This work shows the need to consider a variety of mechanisms to understand the tribovoltaic effect and design future exemplar tribovoltaic devices.

Tunable Tribovoltaic Effect via Metal-Insulator Transition

Tribovoltaic direct-current (DC) nanogenerator made of dynamic semiconductor heterojunction is emerging as a promising mechanical energy harvesting technology. However, fundamental understanding of the mechano-electronic carrier excitation and transport at dynamic semiconductor interfaces remains to be investigated. Here, we demonstrated for the first time, that tribovoltaic DC effect can be tuned with metal-insulator transition (MIT). In a representative MIT material (vanadium dioxide, VO₂), we found that the short-circuit current (I_SC) can be enhanced by >20 times when the material is transformed from insulating to metallic state upon static or dynamic heating, while the open-circuit voltage (V_OC) turns out to be unaffected. Such phenomenon may be understood by the Hubbard model for Mott insulator: orders' magnitude increase in conductivity is induced when the nearest hopping changes dramatically and overcomes the Coulomb repulsion, while the Coulomb repulsion giving rise to the quasi-particle excitation energy remains relatively stable.

Broadband Insulator-Based Dynamic Diode with Ultrafast Hot Carriers Process

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.