Citation: Widakdo, J.; Lei, W.-C.; Anawati, A.; Thagare Manjunatha, S.; Austria, H.F.M.; Setiawan, O.; Huang, T.-H.; Chiao, Y.-H.; Hung,W.-S.; Ho, M.-H. Effects of Co-Solvent-Induced Self-Assembled Graphene-PVDF Composite Film on Piezoelectric Application. Polymers 2023, 15, 137. https://doi.org/10.3390/ polym15010137 Academic Editors: Sofia Rangou and Volkan Filiz Received: 22 November 2022 Revised: 21 December 2022 Accepted: 23 December 2022 Published: 28 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Effects of Co-Solvent-Induced Self-Assembled Graphene-PVDF Composite Film on Piezoelectric Application Januar Widakdo 1,3 , Wen-Ching Lei 2 , Anawati Anawati 3 , Subrahmanya Thagare Manjunatha 1 , Hannah Faye M. Austria 1 , Owen Setiawan 1 , Tsung-Han Huang 1 , Yu-Hsuan Chiao 4,5, * , Wei-Song Hung 1, * and Ming-Hua Ho 2, * 1 Advanced Membrane Materials Research Center, Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106335, Taiwan 2 Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10617, Taiwan 3 Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok 16424, Indonesia 4 Research Center for Membrane and Film Technology, Kobe University, Kobe 657-8501, Japan 5 Department of Chemical Science and Engineering, Kobe University, Kobe 657-8501, Japan * Correspondence: ychiao@people.kobe-u.ac.jp (Y.-H.C.); wshung@mail.ntust.edu.tw (W.-S.H.); mhho@mail.ntust.edu.tw (M.-H.H.) Abstract: A persistent purpose for self-powered and wearable electronic devices is the fabrication of graphene-PVDF piezoelectric nanogenerators with various co-solvents that could provide enhanced levels of durability and stability while generating a higher output. This study resulted in a piezoelec- tric nanogenerator based on a composite film composed of graphene, and poly (vinylidene fluoride) (PVDF) as a flexible polymer matrix that delivers high performance, flexibility, and cost-effectiveness. By adjusting the co-solvent in the solution, a graphene-PVDF piezoelectric nanogenerator can be created (acetone, THF, water, and EtOH). The solution becomes less viscous and is more diluted the more significant the concentration of co-solvents, such as acetone, THF, and EtOH. Additionally, when the density is low, the thickness will be thinner. The final film thickness for all is ~25 μm. Furthermore, the- crystal phase becomes more apparent when graphene is added and combined with the four co-solvents. Based on the XRD results, the peak changes to the right, which can be inferred to be more dominant with the β-phase. THF is the co-solvent with the highest piezoelectric output among other co-solvents. Most of the output voltages produced are 0.071 V and are more significant than the rest. Keywords: PVDF; graphene; piezoelectric; composite film application; sensor 1. Introduction An attractive possibility for producing electricity is to capture mechanical energy from the vibrations in the surroundings that would otherwise go to waste. Piezoelectric [1], triboelectric [2,3], and other technologies can be used for mechanical energy harvesting. Due to its high output, ease of fabrication, and straightforward design, mechanical energy harvesting via the piezoelectric approach is particularly intriguing [4,5]. In addition, piezoelectric nanogenerators (PENGs) are adaptable, extremely effective, and mechanically durable tools that may supply electrical energy to autonomous systems [6,7]. A piezoelectric polymer called poly (vinylidene fluoride) (PVDF) is a prime candidate for use in mechanical energy harvesting based on the piezoelectric effect [8,9]. Mechanical strength, chemical stability, and biocompatibility are three of PVDF’s many benefits, making it a prime choice for mechanical energy harvesting by creating a piezoelectric nanogenerator (PENG) to supply electricity to electronic devices. A polymer with a repeating unit of (CH 2 –CF 2 ) n is called PVDF [10,11]. It demonstrates muscular mechanical strength, excellent thermal stability, good chemical resistance, and Polymers 2023, 15, 137. https://doi.org/10.3390/polym15010137 https://www.mdpi.com/journal/polymers