摩擦奈米發電機(TENG)是一種新型發電技術，透過材料的微觀結構，在機械運動的過程中產生靜電效應，進而將機械能轉換為電能。與傳統發電機不同，TENG具有體型小巧輕便、易於集成和低成本生產等優勢，並且不需外部能源輸入，在現今能源短缺的時代中，摩擦奈米發電機可以作為一項綠色能源的選擇，並且特別適用於穿戴式設備、智能感測器與自動控制系統等應用領域。
傳統交流電摩擦奈米發電機(AC-TENG)雖然具備高輸出電壓與低輸出電流的優點，但由於其工作電阻非常高，限制了其實際應用，因此，近年來直流型摩擦奈米發電機(DC-TENG)成為研究熱點，其核心基制式基於摩擦伏特效應(Tribovoltaic effect)，透過半導體與半導體(S-S)或者是半導體和金屬(M-S)接觸的摩擦滑動，利用對擦材料的費米能階差異產生內建電場，進一步分離摩擦所激發的電子電洞對，進而實現直流輸出。
本研究將藉由使用金屬-半導體接觸與半導體-半導體接觸兩種摩擦滑動形式，半導體材料選擇有N/P型矽基板、氧化鋅薄膜、銅摻雜氧化鋅摩擦在氧化鋅鎂，每種材料各自的功函數與費米能階大小不盡相同，因此會藉由直流型摩擦奈米發電機之輸出電壓電流大小，並探討不同材料之間摩擦後，影響電性輸出之因素，分析材料間的電子傳輸型為，以及不同對擦元件的材料性質如何影響摩擦伏特效應之機制理論分析。

A triboelectric nanogenerator (TENG) is an innovative technology that converts mechanical energy into electrical energy through friction-induced charge transfer. Based on the microstructural properties of materials, TENG utilizes surface interactions during mechanical motion to generate electrostatic charges, ultimately transforming kinetic energy into electrical energy. The working principle of TENGs is based on the triboelectric effect, where materials with different electron affinities exchange charges upon contact and separation. These triboelectric charges create a potential difference, driving an electrical current through an external circuit. Unlike conventional power generators, TENGs offer significant advantages, including compact size, lightweight design, easy integration, and low production costs. Additionally, they do not require an external power source, making them a promising alternative in the current era of energy shortages, TENGs are ideal for self-powered systems in wearable devices, intelligent sensors, biomedical devices and autonomous control systems. Their ability to generate electricity from small mechanical movements makes them an attractive solution in an era where sustainable and green energy sources are in high demand.
Traditional alternating current (AC) triboelectric nanogenerators exhibit notable advantages, such as high output voltage and low output current. However, a significant drawback of AC-TENGs is their high output impedance, which imposes considerable limitations on their practical applications, particularly in energy harvesting and storage. Additionally, AC-TENGs require rectification circuits to convert their AC output into DC, which adds complexity and energy loss to the system. To overcome this challenges, direct current (DC) triboelectric nanogenerators(DC-TENGs) have been developed, which provide a more direct and stable energy output. The working mechanism of DC-TENGs is fundamentally different from that of AC-TENGs, as it leverages the tribovoltaic effect, a newly discovered charge generation process that occurs at the interface of two materials with differing Fermi levels.
The core mechanism of DC-TENG is based on the tribovoltaic effect, which occurs when a semiconductor-to-semiconductor (S-S) or metal-to-semiconductor (M-S) contact is subjected to frictional motion. The key principle relies on the difference in Fermi levels between the two triboelectric materials. During the friction process, the energy transfer between the materials induces electron-hole pair generation, and the built-in electric field at the interface facilitates charge separation, thereby producing a continuous DC output. This process differs significantly from conventional TENGs, which rely solely on electrostatic induction. Instead, the tribovoltaic effect directly generates a flow of charge carriers, making it a promising approach for improving energy conversion efficiency in triboelectric nanogenerators.
This study aims to explore the electrical output characteristics of DC-TENGs by employing two types of triboelectric sliding configurations: Metal-Semiconductor (M-S) Contact and Semiconductor-Semiconductor (S-S) Contact, and for the semiconductor materials, the following components are selected : N-type and P-type silicon substrates, Zinc oxide thin films, Copper-doped zinc oxide and Magnesium-doped zinc oxide thin films. Since each of these materials has a distinct work function and Fermi level, their triboelectric interactions are expected to exhibit different electrical behaviors. To comprehensively analyze the tribovoltaic effect, this research focuses on the output voltage and current characteristic of DC-TENGs under different triboelectric material pairings.
There are several key factors that influence the efficiency and effectiveness of DC-TENGs. First is Work function Fermi level differences, the difference in work function between two materials determines the strength of the built-in electric field, which affects the charge separation efficiency, a larger Fermi level mismatch generally results in a higher output voltage. Second is Charge carrier generation and transport, materials with higher electron mobility allow faster charge transport, leading to improved current output, semiconductor doping can alter carrier concentration, impacting charge separation efficiency. Third one is Interface and Surface states, the presence of interface states and surface roughness can impact charge transfer, a smooth interface enhances carrier separation, while a rough interface increases charge trapping, affecting efficiency. The last is Contact force and sliding speed, higher contact pressure increases the effective contact area, enhancing charge transfer, faster sliding speed induce more frequent charge generation cycles, boosting power output.
The key research objectives include investigating how friction-induced charge transfer caries based on material properties, examining the impact of different triboelectric material combinations on the magnitude of electrical output and understanding how semiconductor doping influences charge generation and separation in triboelectric interfaces. The findings from this study will contribute to a deeper theoretical understanding of DC-TENGs and their dependence on material properties. Moreover, practical advancements in energy harvesting technologies can be achieved, enabling improved energy storage integration through stable DC output, development of self-powered electronic systems, reducing reliance on conventional batteries, enhanced performance of wearable and flexible electronics, providing a sustainable energy solution.
By optimizing, the tribovoltaic effect represents a significant breakthrough in triboelectric nanogenerator technology, enabling direct DC power generation with improved efficiency. By selecting optimal semiconductor materials and understanding the fundamental mechanisms of charge transfer, researchers can further enhance DC-TENG performance for real-world applications. Future research can focus on developing advanced material engineering strategies to optimize charge transport and carrier mobility, exploring novel semiconductor heterojunctions to increase Fermi level differences and improve power output, integrating DC-TENGs with energy storage systems such as super capacitors and batteries to create more robust energy solutions. With continuous advancements in material science and device engineering, DC-TENGs have the potential to revolutionize self-powered electronics, contributing to a sustainable and energy efficient future.

[1] F. Ghahramanifard, A. Rouhollahi, and O. Fazlolahzadeh, "Electrodeposition of Cu-doped p-type ZnO nanorods; effect of Cu doping on structural, optical and photoelectrocatalytic property of ZnO nanostructure," Superlattices and Microstructures, vol. 114, pp. 1-14, 2018.
[2] P. Shewale and Y. Yu, "Structural, surface morphological and UV photodetection properties of pulsed laser deposited Mg-doped ZnO nanorods: effect of growth time," Journal of Alloys and Compounds, vol. 654, pp. 79-86, 2016.
[3] P. Jongnavakit, P. Amornpitoksuk, S. Suwanboon, and N. Ndiege, "Preparation and photocatalytic activity of Cu-doped ZnO thin films prepared by the sol–gel method," Applied Surface Science, vol. 258, no. 20, pp. 8192-8198, 2012.
[4] K. Huang et al., "Preparation and characterization of Mg-doped ZnO thin films by sol–gel method," Applied Surface Science, vol. 258, no. 8, pp. 3710-3713, 2012.
[5] Z. Zhang et al., "Tribovoltaic effect on metal–semiconductor interface for direct‐current low‐impedance triboelectric nanogenerators," Advanced Energy Materials, vol. 10, no. 9, p. 1903713, 2020.
[6] J. Meng et al., "Coupling of tribovoltaic effect and tribo-electrostatic effect at dynamic semiconductor heterojunction interfaces," Nano Energy, vol. 133, p. 110395, 2025.
[7] J. Wang et al., "Achieving ultrahigh triboelectric charge density for efficient energy harvesting," Nature communications, vol. 8, no. 1, p. 88, 2017.
[8] Ü. Özgür et al., "A comprehensive review of ZnO materials and devices," Journal of applied physics, vol. 98, no. 4, 2005.
[9] A. J. Kulandaisamy et al., "Room temperature ammonia sensing properties of ZnO thin films grown by spray pyrolysis: Effect of Mg doping," Journal of Alloys and Compounds, vol. 688, pp. 422-429, 2016.
[10] F.-R. Fan, Z.-Q. Tian, and Z. L. Wang, "Flexible triboelectric generator," Nano energy, vol. 1, no. 2, pp. 328-334, 2012.
[11] Z.-H. Lin, Y. Xie, Y. Yang, S. Wang, G. Zhu, and Z. L. Wang, "Enhanced triboelectric nanogenerators and triboelectric nanosensor using chemically modified TiO2 nanomaterials," ACS nano, vol. 7, no. 5, pp. 4554-4560, 2013.
[12] S. Kim et al., "Transparent flexible graphene triboelectric nanogenerators," Advanced materials, vol. 26, no. 23, pp. 3918-3925, 2014.
[13] Y. H. Ko, G. Nagaraju, S. H. Lee, and J. S. Yu, "PDMS-based triboelectric and transparent nanogenerators with ZnO nanorod arrays," ACS applied materials & interfaces, vol. 6, no. 9, pp. 6631-6637, 2014.
[14] X.-S. Zhang et al., "High-performance triboelectric nanogenerator with enhanced energy density based on single-step fluorocarbon plasma treatment," Nano Energy, vol. 4, pp. 123-131, 2014.
[15] X. He, H. Guo, X. Yue, J. Gao, Y. Xi, and C. Hu, "Improving energy conversion efficiency for triboelectric nanogenerator with capacitor structure by maximizing surface charge density," Nanoscale, vol. 7, no. 5, pp. 1896-1903, 2015.
[16] Y. Liu et al., "Enhancement of triboelectric charge density by chemical functionalization," Advanced Functional Materials, vol. 30, no. 50, p. 2004714, 2020.
[17] C. K. Jeong et al., "Topographically-designed triboelectric nanogenerator via block copolymer self-assembly," Nano letters, vol. 14, no. 12, pp. 7031-7038, 2014.
[18] S. Niu et al., "A theoretical study of grating structured triboelectric nanogenerators," Energy & Environmental Science, vol. 7, no. 7, pp. 2339-2349, 2014.
[19] W. Yang et al., "3D stack integrated triboelectric nanogenerator for harvesting vibration energy," Advanced Functional Materials, vol. 24, no. 26, pp. 4090-4096, 2014.
[20] Y. Xie et al., "Multi-layered disk triboelectric nanogenerator for harvesting hydropower," Nano Energy, vol. 6, pp. 129-136, 2014.
[21] J. Chun et al., "Boosted output performance of triboelectric nanogenerator via electric double layer effect," Nature communications, vol. 7, no. 1, p. 12985, 2016.
[22] J. Liu et al., "Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS2 multilayers," Nature nanotechnology, vol. 13, no. 2, pp. 112-116, 2018.
[23] M. Zheng, S. Lin, L. Xu, L. Zhu, and Z. L. Wang, "Scanning probing of the tribovoltaic effect at the sliding interface of two semiconductors," Advanced Materials, vol. 32, no. 21, p. 2000928, 2020.
[24] Z. Zhang, T. He, J. Zhao, G. Liu, Z. Wang, and C. Zhang, "Tribo-thermoelectric and tribovoltaic coupling effect at metal-semiconductor interface," Materials Today Physics, vol. 16, p. 100295, 2021.
[25] Z. L. Wang and A. C. Wang, "On the origin of contact-electrification," Materials Today, vol. 30, pp. 34-51, 2019.
[26] Y. Chen et al., "Friction-dominated carrier excitation and transport mechanism for GaN-based direct-current triboelectric nanogenerators," ACS Applied Materials & Interfaces, vol. 14, no. 20, pp. 24020-24027, 2022.
[27] Z. Wang et al., "Achieving an ultrahigh direct-current voltage of 130 V by semiconductor heterojunction power generation based on the tribovoltaic effect," Energy & Environmental Science, vol. 15, no. 6, pp. 2366-2373, 2022.
[28] Q. Zhang, R. Xu, and W. Cai, "Pumping electrons from chemical potential difference," Nano Energy, vol. 51, pp. 698-703, 2018.
[29] S. Lin, X. Chen, and Z. L. Wang, "The tribovoltaic effect and electron transfer at a liquid-semiconductor interface," Nano Energy, vol. 76, p. 105070, 2020.
[30] M. Zheng, S. Lin, Z. Tang, Y. Feng, and Z. L. Wang, "Photovoltaic effect and tribovoltaic effect at liquid-semiconductor interface," Nano Energy, vol. 83, p. 105810, 2021.
[31] K. Kristiansen, H. Zeng, P. Wang, and J. N. Israelachvili, "Microtribology of aqueous carbon nanotube dispersions," Advanced Functional Materials, vol. 21, no. 23, pp. 4555-4564, 2011.
[32] Z. Xu and P. Huang, "Study on the energy dissipation mechanism of atomic-scale friction with composite oscillator model," Wear, vol. 262, no. 7-8, pp. 972-977, 2007.
[33] K. Nakayama and H. Hashimoto, "Triboemission, tribochemical reaction, and friction and wear in ceramics under various n-butane gas pressures," Tribology international, vol. 29, no. 5, pp. 385-393, 1996.
[34] M. Srinivasan and S. Walcott, "Binding site models of friction due to the formation and rupture of bonds: state-function formalism, force-velocity relations, response to slip velocity transients, and slip stability," Physical Review E—Statistical, Nonlinear, and Soft Matter Physics, vol. 80, no. 4, p. 046124, 2009.
[35] A. Filippov, J. Klafter, and M. Urbakh, "Friction through dynamical formation and rupture of molecular bonds," Physical Review Letters, vol. 92, no. 13, p. 135503, 2004.
[36] K. Tian, N. N. Gosvami, D. L. Goldsby, Y. Liu, I. Szlufarska, and R. W. Carpick, "Load and time dependence of interfacial chemical bond-induced friction at the nanoscale," Physical Review Letters, vol. 118, no. 7, p. 076103, 2017.
[37] A. Li, Y. Liu, and I. Szlufarska, "Effects of interfacial bonding on friction and wear at silica/silica interfaces," Tribology letters, vol. 56, pp. 481-490, 2014.
[38] M. Zheng, S. Lin, L. Zhu, Z. Tang, and Z. L. Wang, "Effects of temperature on the tribovoltaic effect at liquid‐solid interfaces," Advanced Materials Interfaces, vol. 9, no. 3, p. 2101757, 2022.
[39] S. Lin and Z. L. Wang, "The tribovoltaic effect," Materials Today, vol. 62, pp. 111-128, 2023.
[40] J. Lowell and A. Rose-Innes, "Contact electrification," Advances in Physics, vol. 29, no. 6, pp. 947-1023, 1980.
[41] S. Lin, C. Xu, L. Xu, and Z. L. Wang, "The overlapped electron‐cloud model for electron transfer in contact electrification," Advanced Functional Materials, vol. 30, no. 11, p. 1909724, 2020.
[42] L. Ren et al., "Pn junction based direct-current triboelectric nanogenerator by conjunction of tribovoltaic effect and photovoltaic effect," Nano Letters, vol. 21, no. 23, pp. 10099-10106, 2021.
[43] W. Qiao et al., "MXene lubricated tribovoltaic nanogenerator with high current output and long lifetime," Nano-Micro Letters, vol. 15, no. 1, p. 218, 2023.
[44] M. Suja, S. B. Bashar, M. M. Morshed, and J. Liu, "Realization of Cu-doped p-type ZnO thin films by molecular beam epitaxy," ACS Applied materials & interfaces, vol. 7, no. 16, pp. 8894-8899, 2015.
[45] M. B. Rahmani et al., "Transition from n-to p-type of spray pyrolysis deposited Cu doped ZnO thin films for NO2 sensing," Sensor Letters, vol. 7, no. 4, pp. 621-628, 2009.
[46] Z. N. Kayani, S. Iram, R. Rafi, S. Riaz, and S. Naseem, "Effect of Cu doping on the structural, magnetic and optical properties of ZnO thin films," Applied Physics A, vol. 124, pp. 1-10, 2018.
[47] B. K. Das, T. Das, K. Parashar, A. Thirumurugan, and S. Parashar, "Structural, bandgap tuning and electrical properties of Cu doped ZnO nanoparticles synthesized by mechanical alloying," Journal of Materials Science: Materials in Electronics, vol. 28, pp. 15127-15134, 2017.
[48] M. Ferhat, A. Zaoui, and R. Ahuja, "Magnetism and band gap narrowing in Cu-doped ZnO," Applied physics letters, vol. 94, no. 14, 2009.
[49] Z. Ma, F. Ren, X. Ming, Y. Long, and A. A. Volinsky, "Cu-doped ZnO electronic structure and optical properties studied by first-principles calculations and experiments," Materials, vol. 12, no. 1, p. 196, 2019.
[50] O. Slimi, D. Djouadi, L. Hammiche, A. Chelouche, and T. Touam, "Structural and optical properties of Cu doped ZnO aerogels synthesized in supercritical ethanol," Journal of Porous Materials, vol. 25, pp. 595-601, 2018.
[51] M. Fu, Y. Li, P. Lu, J. Liu, and F. Dong, "Sol–gel preparation and enhanced photocatalytic performance of Cu-doped ZnO nanoparticles," Applied Surface Science, vol. 258, no. 4, pp. 1587-1591, 2011.
[52] M. Rouchdi, E. Salmani, B. Fares, N. Hassanain, and A. Mzerd, "Synthesis and characteristics of Mg doped ZnO thin films: Experimental and ab-initio study," Results in physics, vol. 7, pp. 620-627, 2017.
[53] V. Etacheri, R. Roshan, and V. Kumar, "Mg-doped ZnO nanoparticles for efficient sunlight-driven photocatalysis," ACS applied materials & interfaces, vol. 4, no. 5, pp. 2717-2725, 2012.
[54] J. Singh et al., "Synthesis, band-gap tuning, structural and optical investigations of Mg doped ZnO nanowires," CrystEngComm, vol. 14, no. 18, pp. 5898-5904, 2012.
[55] R. Sagheer, M. Khalil, V. Abbas, Z. N. Kayani, U. Tariq, and F. Ashraf, "Effect of Mg doping on structural, morphological, optical and thermal properties of ZnO nanoparticles," Optik, vol. 200, p. 163428, 2020.
[56] P. Wang, N. Chen, Z. Yin, R. Dai, and Y. Bai, "p-type Zn1− xMgxO films with Sb doping by radio-frequency magnetron sputtering," Applied physics letters, vol. 89, no. 20, 2006.
[57] X. Wang et al., "The impacts of growth temperature on morphologies, compositions and optical properties of Mg-doped ZnO nanomaterials by chemical vapor deposition," Journal of Alloys and Compounds, vol. 622, pp. 440-445, 2015.
[58] M. N. H. Mia et al., "Influence of Mg content on tailoring optical bandgap of Mg-doped ZnO thin film prepared by sol-gel method," Results in physics, vol. 7, pp. 2683-2691, 2017.