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

Abstract

Interfacial layer engineering has been demonstrated as an effective strategy for boosting power output in semiconductor-based dynamic direct-current (DC) generators, although the underlying mechanism of power enhancement remains obscure. Here, such ambiguity has been elucidated by comparing fundamental tribovoltaic DC output characteristics of prototypical metal–oxide–metal heterojunctions prepared by atomic-layer deposition (ALD) with a vertical (out-of-plane carrier transport through the interfacial layer) and a horizontal (in-plane carrier transport along the interfacial layer) configuration such that the influences from nonequilibrium electronic excitation and interfacial capacitive amplification can be individually tuned and investigated. It is found in the case of Al/TiO2/Ti vertical configurations that the open-circuit voltage (V OC) increases linearly from −0.03 to −0.52 V as the thickness of titanium oxide (t TiO2 ) increases from 0 to 200 nm with a linear amplification coefficient of −2.31 mV nm–1, which is validated by a parallel-capacitor theoretical model with tribovoltaic electronic excitation. In contrast, the V OC output with the horizontal configuration is ∼55 mV, where the potential difference is merely associated with the accumulation of surface charges and the subsequent charge rearrangement in the depletion region. Meanwhile, it is measured that the short-circuit current density (J SC) shows an initial increasing trend when t TiO2 increases, reaches its peak value at 0.21 A m–2 at t TiO2 = 20 nm, and then decreases as t TiO2 increases further. From current–voltage (I–V) characterization, it is proposed that such DC output variation with an optimal interfacial layer thickness stems from the competition of amplified voltage and increased resistance with increasing interfacial layer thickness, with the main charge transport mechanism switching from quantum tunneling to thermionic emission/trap-assisted transport. In contrast, tribovoltaic excitation is proven to be significantly weaker when a wide band-gap insulator (Al2O3) is involved. The elucidation of the fundamental mechanism of power enhancement by the interfacial layer in this work is of great significance in providing instructional direction for the development and optimization of high-performance DC nanogenerators.

Simultaneously Enhancing Direct‐Current Density and Lifetime of Tribovotaic Nanogenerator via Interface Lubrication

“…Tribovoltaic nanogenerator (TVNG) can generate direct-current (DC) due to the tribovoltaic effect, which has great features of low matching resistance, high current density, and continuous output performance, showing its great potential to solve the power supply problem for distributed electronic devices. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] However, the solidsolid hard contact of TVNG will cause the interlocking between atoms on the contact interface, resulting in the increase of friction stress and aggravation of wear problem. [28] The severe wear problem will cause rapid attenuation of output performance, thus, it is difficult for TVNG to realize long-term operation with high current density.…”

A Rolling‐Mode Al/CsPbBr3 Schottky Junction Direct‐Current Triboelectric Nanogenerator for Harvesting Mechanical and Solar Energy

“…[ 50 ] This may cause the valence electrons in the excited state to move from the valence band to the conduction band (band‐to‐band transition), from the valence band to the surface state (sub‐band‐gap transition), or from the surface state to the conduction band (sub‐band‐gap transition). [ 43 ] Under the built‐in electric field, electrons and holes move in different directions to form DC. Furthermore, the energy released during the friction process enables electrons in the surface states of Al and CsPbBr 3 to transition to higher energy levels.…”

“…[41] Currently, metal-or semiconductor-based dynamic heterojunctions are an emerging strategy for high DC mechanical energy harvesting. [42,43] Herein, we have innovatively devised an all-inorganic perovskite rolling-mode multifunctional DC-TENG for simultaneously harvesting mechanical and solar energy by constructing a dynamic Al/CsPbBr 3 Schottky junction. Rolling Al on the CsPbBr 3 film under AM 1.5 light illumination, the output current density could reach 11.46 A m −2 , which is 4.7 times higher than that under dark condition.…”

“…[ 41 ] Currently, metal‐ or semiconductor‐based dynamic heterojunctions are an emerging strategy for high DC mechanical energy harvesting. [ 42,43 ]…”

Broadband Insulator-Based Dynamic Diode with Ultrafast Hot Carriers Process

“…Recently, Liu et al report the possible mechanism of vertical/horizontal structure DD based on TiO 2 and Al 2 O 3 , which are also well-known insulator materials. Interestingly, the TiO 2 -based device shows higher electricity output than Al 2 O 3 -based device of the same interfacial dielectric thickness (tens of nm) [ 27 ], which indicates that oxygen vacancy defect plays an important role in the carrier transport inside insulators. These results are also strong evidence for our proposed HCs rebound-hopping-like through insulator theory above.…”