![]() And additional requirement such as long-lasting heating or poling may impede the large-area processing and uniform distribution of PVDF films. However, the electrospinning and solvent-casting usually induce some undesired structure deformation or microstructure defeats. According to the research report on the electrospinning process of the high β-phase PVDF membrane, the micro-patterned device as an energy harvester can generate an open circuit voltage density of 1.42 V m −2 ( Fadzallah et al., 2020). Besides, special treatment including electrospinning ( Li et al., 2008), solvent-casting ( Hu et al., 2015), mechanical stretching, and polarization under high electric fields ( Fukada and Sakurai., 1971 Cheng-Lu et al., 2014) of PVDF ( Sencadas et al., 2009 Sharma et al., 2013 Won et al., 2016) have been employed. Copolymers of PVDF, such as P(VDF-TrFE), have been synthesized to achieve an intrinsic β-phase crystal. In order to increase the β-phase and simultaneously reduce the crystallinity of the α-phase, many methods have been developed during the preparation of PVDF materials. By thermal treatment ( Prest and Luca., 1978) or poling under a high electric field (150kV/mm) ( Davis et al., 1978 Banik et al., 1980), the α-phase can be transformed to the γ-phase or β-phase. However, the α-phase is the most favorite form in thermodynamics with nonpolar crystalline phases. The β-phase has an all trans (TTTT) planar zigzag with the strongest polarity, while the γ-phase ( Hasegawa et al., 1972 Masahiko et al., 1977 Lovinger, 1983 Sajkiewicz et al., 1999) displays a T 3GT 3G chain conformation which is partially polar. The nonpolar α-phase has a TGTG chain conformation, resulting in the self-cancelation of dipoles ( Lovinger et al., 1983). As a semicrystalline polymer, PVDF presents a complex crystalline structure and crystalline phases (commonly α-, β-, and γ-) ( Dai et al., 2016). The piezoelectricity of PVDF originates from its crystalline structures. Thus, it is vital to improve the piezoelectric properties of PVDF to promote its value in the smart wearable device applications. As the most studied polymer for PENG, PVDF-TrFE has relative low remnant polarization and piezoelectric coefficient but irreplaceable flexibility and transparency ( Chan et al., 2003 Pi et al., 2014 Mcginn et al., 2020). With the rapid development of smart wearable devices, the energy conversion efficiency, flexibility, and transparency are the most important features of PENGs. Recently, the PENGs are used as power sources to drive the low-power wearable devices. The piezoelectricity allows it to convert the ambient mechanical stimulations to electricity, which has been widely used in energy harvesting applications such as the piezoelectric nanogenerators (PENGs). Since Kawai initially reported the poly(vinylidene fluoride) (PVDF) in 1969 ( Moyle, 1969), PVDF has attracted considerable attention ( Furukawa, 1989 Bune et al., 1998) owing to its unique piezoelectricity. Besides, the obtained PVDF-TrFE films present a good piezoelectric response to different extents of mechanical stimulations, which have great potential in energy harvesting applications. The processing influence of drying, annealing, and poling on the crystalline properties and piezoelectric performances were investigated. ![]() ![]() Compared with traditional poling methods, the in situ polarization is performed with low poling voltage and short poling time, and it can ensure the PVDF-TrFE film with enhanced piezoelectric performances and uniform distribution among a large area of 200 mm 2 × 200 mm 2. ![]() The d 33 coefficient = 28 pC/N of PVDF-TrFE piezoelectric films was achieved by the in situ polarization. 3Sichuan Flexible Display Materials Genome Engineering Center, Chengdu, China.2Advanced Energy Institute, University of Electronic Science and Technology of China, Chengdu, China.1School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu, China.Xiaoran Hu 1,2 Mengli You 1,2 Na Yi 1,2 Xiaokun Zhang 1,2* Yong Xiang 1,2,3
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