柔性电子：P(VDF-TrFE)/BaTiO3复合微柱阵列用于自供能柔性传感器

通过纳米压缩工艺制作piezoelectrically enhanced verticallyaligned P(VDF-TrFE)/BaTiO3 nanocomposite micropillar arrays

制作工艺：

$P(VDF-TrFE)/BaTiO_3$ 的制造：纳米复合材料薄膜：
$P (V D F - T r F E)$ 粉末【昆山海信电子有限公司】和 $BaTiO_3$ 纳米颗粒【Nanostructured & Amorphous Materials, Inc】的摩尔比为70/30。 $BaTiO_3$ 纳米颗粒的平均直径为200nm。
首先间 $BaTiO_3$ 纳米颗粒与DMF混合，超声搅拌2h，【ultrasonic stirred for 2 h to separate aggregated NPs】。
$P (V D F - T r F E)$ 粉末与 $BaTiO_3$ 加入到DMF中，【P(VDF-TrFE) powders were then added to produce solutions with a predefined 0–50 wt % of BaTiO3 NPs with respect to P(VDF-TrFE)】在60度的温度下搅拌2h获得均匀溶液。
通过旋涂的方式将溶液沉积到底部电极上，在140度下退火2h
之后测试获得最好的掺杂比例

表征

使用示波器测试压电输出

使用100 M $Ω\Omega$ 的探针记录压电电压，使用低噪声电流前置放大器(斯坦福)记录电流，在极化过程中使用的电压由amplifier/controller(TREK 610H.V.)提供，

SEM图像，
XRD图像
拉曼光谱

纳米材料的截面和3D轮廓：LSCM(Olympus OLS4000)

$BaTiO_3$ 的作用使用极化磁滞回路(polarization hysteresis loops, P-E loops)描述

TF Analyzer 2000 ferroelectric test system在样本的底和顶电极时间从-100到100 MV/m的三角脉冲实现。

introduction

首先介绍清洁能源出现的必要性:
[Considering the tremendous growth of the portable electronics and possible depletion of fossil energy resources in the future, the development of sustainable and green energy is extremely urgent[1-4]]

接下来介绍纳米级能量收集势头很猛：[Smart nanogenerators have been aggressively investigated for harvesting energy sources including solar energy, thermal energy, and mechanical energy in our living surrounding for realizing self -powered electronic systems, which is a greatly desired concept for developing wireless sensor networks, wearable biomedical devices, and next-generation personal electronics.[5-8]]

之后将机械能最丰富【可以依靠机械振动收集】：
[Mechanical energy with various types such as sound waves, mechanical impacts flowing air, and human motions are most abundant energy in our living surrounding ]

收集此类的能量依靠压电效应：
[In this framework, flexible piezoelectric
nanogenerators (PENGs), rely on piezoelectric potential generated in piezoelectric materials as a response to applied strain, have attracted extensive attentions.]

讲述其优势：
[Their relatively small size factor, simple structure, and long-term stability make them favorable for use in powering micro/nanosystems, various small power consumer devices, remote and mobile sensors, and even wearable wireless electronics[9-12]]

另一个优势，不仅供能，还能够作为自供电的压力传感器件：高灵敏度，快速响应
[In particular, the output from the flexible piezoelectric nanogenerators not just limited in energy-harvesting purpose, the
ability of piezoelectric materials to generate different levels of electricity in response to various mechanical stimuli with high sensitivity and fast response time enabled the realization of self-powered piezoelectric e-skins with tactile sensing capabilities.[13-17]]

之后介绍一些实例：
[n fact, it has recently been demonstrated
as a sensor signal for detecting the mechanical deformation, such as monitoring tire pressure,[18] transportation,[19] ambient wind-velocity detection,[20] and skin deformation.[21]]

之后介绍常用的压电材料：
无机压电材料
有好的压电特性但是脆性太高
[Among the wide variety of piezoelectric materials available, inorganic piezoelectric materials, such as
barium titanate (BaTiO3),[22]
lead zirconate titanate (PZT),[23]
lead magnesium niobate-lead titanate (PMN-PT),[24]
sodium niobate (NaNbO3),[25]
zinc stannate (ZnSnO3)[26]
exhibit high level of inherent piezoelectric characteristics, but their intrinsic rigid nature restricts their application in flexible e-skins]

之后又介绍了铁电高分子聚合物材料：
[By the other side, polyvinylidene fluoride (PVDF) and its copolymer polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) show mechanical better flexibility, processing simplicity, and excellent biocompatibility, are ideal candidate sensing materials for large area tactile sensors and energy harvesting from human activities[27-29]]

这种材料铁电性能很差：
[However, due to the lower piezoelectricity of PVDF and its copolymers, most PENGs based on these ferroelectric polymers have shown much lower power outputs than those of inorganic PENGs, which is insufficient to operate the self-powered electronics continuously]

最后一句客套话，一直在努力：
[There has since been an ongoing concerted effort in developing high performance piezoelectric device in order to enhance their mechanical flexibility, power-generating performance, and sensitivity as flexible sensors]

说一下解决方案，和之前的相关的论文工作：
[To address these issues, some strategies have been promoted. The hybridization of composites of high piezoelectric inorganic fillers and high flexibility polymer matrix has been widely adopted to impart flexibility and robustness with good performance. In this respect, there have been several reports of nanocomposite nanogenerators based on PVDF,[30,31] polydimethylsiloxane (PDMS),[32,33] polyurethane[34] as the flexible matrix and piezoelectric micro/nanostructures, such as BaTiO3 nanoparticles (NPs),[30] NaNbO3 nanowires,[35] Na0.47K0.47Li0.06NbO3 (NKLN) microcubes,[36] and porous cellulose nanofibril (CNFs)[37] as piezoelectric fillers]

说BaTiO3的好处：无铅，压电系数高
[Among them, BaTiO3 as a lead-free material with high piezoelectric coefficient has been widely used to realize nanocomposite nanogenerator]

几种PENGs器件的比较在Table S1中。

点了一下优点：
[These developed piezoelectric nanocomposites have successfully demonstrated good piezoelectric properties and mechanical robustness toward flexible and wearable applications.[38–48]]

除了压电复合材料，在压电材料中形成微/纳米结构也可提高压电性能。
[Besides piezoelectric nanocomposite, the formation of micro/nanostructures in piezoelectric materials is another expansion to improve the piezoelectric performance.[ 48–50]

对于微小力的高响应性：
[Since the first ZnO nanowire-based nanogenerator was demonstrated in 2006, there has been ardent research using various piezoelectric micro/nanostructures for self-powered systems due to their size effect, higher mechanical flexibility, better strain confinement and higher sensitivity
to small forces.[51–54]]

微结构的缺点：复杂的制作流程
[Although various forms of piezoelectric
micro/nanostructures have shown enhanced performance compared with bulk materials, but they normally require
complicated synthesis and assembly procedures like transfer, cast-etching, high-temperature annealing, difficulty in device integration, and sophisticated equipment to position, thereby limiting their mechanical flexibility as well as their potential applications.[13]]

客套话：实现两方面都好的

[Therefore, the development of durable, high sensitive and efficient piezoelectric energy harvesting devices with a reliable and low-cost fabrication approach is necessary to realize various self-powered sensing device applications]

之后介绍本论文的工作：
使用什么材料制造了什么样的器件：
[In this paper, a high performance flexible piezoelectric nanogenerator is demonstrated, based on a piezoelectrically enhanced nanocomposite micropillar array of BaTiO3 nanoparticles embedded into a highly crystalline P(VDF-TrFE) polymer for efficient energy harvesting and highly sensitive self-powered sensing.]

制造过程简单：
[The piezoelectrically enhanced P(VDFTrFE)/ BaTiO3 micropillars were fabricated via a facile, reliable, and scalable nanoimprinting process to further improve their performance for designing the PENGs and flexible pressure sensors.]

优点：垂直排列的结构导致的：
[The vertically well-aligned structure of
the P(VDF-TrFE)/BaTiO3 nanocomposite micropillar array results in a macroscopic piezopotential that can produce a peak output voltage of 13.2 V and an average current density of 0.33 μA cm− 2, therefore the piezoelectric voltage was enhanced to 7.3 times that of the pristine P(VDF-TrFE) flat film under the same vertical compressive force]

主要做了哪些工作：
P-E 磁滞曲线测试；
能点亮LCD和LED而不需要存储单元
电压存储到商用电容器中，驱动电子产品
高灵敏度传感器
作为可穿戴设备，检测一些生命体征的信号

[The polarization versus electric field (P–E) hysteresis loops test and COMSOL simulation were employed to study the mechanism of output enhancement.
The energy generated from the device can light a liquid crystal display (LCD) screen and arrays of light-emitting diode (LED) bulbs instantaneously without any storage unit.
Besides, the outputs generated are successfully stored in a commercial capacitor and use to drive consumer electronic devices (such as a digital watch, and a music player) to work continuously, implying their significance in the field of consumer electronic devices.
Furthermore, we show that the high-performance flexible PENG can be used as highly sensitive self-powered sensor work in a noncontact mode for detecting air pressure/flow.
It also can be used for wearable sensors for detecting some vital signals including breathing, heartbeating, which shows its possible applications in wearable electronics and medical sciences]

结果和讨论

将配好的最优配比的溶液旋涂到底部柔性电极上

蒸发溶剂后，将PDMS微孔模型在160摄氏度下压在薄膜上，这个温度高于薄膜的融化温度，会最终形成微柱形状。(Figure 1c)

PDMS模具制作过程在Figure S1中，

Figure 1d：在140摄氏度下退火4h，后移除PDMS，制成微柱结构。

之后将PDMS绝缘层旋涂到微柱顶部，5000rpm， 90s。用处：在极化过程中的电稳定性和压电器件的机械耐久度

快速旋涂的目的：填充间隙，但是顶部不完全覆盖，与顶部电极形成直接的电接触。

在不平坦的表面，传统方法很难组装稳定柔软的顶部电极。
使用CNTs。

the MWCNT solution was coating on the top of the surface by the Meyer rod coating method。
具体的流程在Figure S2和S3。

最后，在50MV/m（Figure 1e）的极化过程后，制成柔性压电器件。

器件由三层组成：

Au覆盖的Kapton作为底电极
$P(VDF-TrFE)/BaTiO_3$ 微柱结构作为感知层
MWCNT作为顶电极

1g展示柔性
1h横截面sEM图
1i 上表面SEM图，表面覆盖完整

a. SEM
a的inset. raman 光谱：四方晶相
b. XRD 更深层次的理解

BaTiO3 NPs与P(VDF-TrFE)的质量比值，
Figure S4不同质量比的电输出对比

当BaTiO3的质量为20 wt%时最大电输出3.2V，为没有BaTiO3的4倍
Figure S5横截面SEM图像，BaTiO3的质量比超过20%导致聚集，会在薄膜中形成裂缝。

c. 微柱图像，平均直径22um，高55um
d. 更高放大倍数的微柱侧视图，均匀分布在薄膜中。

d的inset展示XRD图像，19.9度的峰值是P(VDF-TrFE)的beta的典型相。22.2°, 31.5°是BaTiO3 NPs的典型相。

ef展示在PDMS副高前后的图像，

f中的inset展示了LSCM拍摄的3D图像。

Figure S6，由于BaTiO3 NPs 和P(VDF-TrFE)的反射率不同，可以发现BaTiO3 NPs均匀的分布在P(VDF-TrFE)纳米微柱上

表征PENG-NG器件的压电性能，Figure S7测试设备。

3(a, b): 1Hz 50N的力重复压缩样本，展示电压，电流特性。1平方厘米，最大电压和电流为13.2v和0.33uA。

进行极性转换测试实验来判断电压全部来自期间的压电特性。【58】Figure S8

Figure 3c，对比图像，微柱结构，薄膜，和原始的P(VDF-TrFE)薄膜，压缩下的最大电压分别为13.2， 6.4， 1.8V。

性能的增强是由于压电性能的增强和微柱阵列在压缩下的机械柔性增强【The superior performance of the sample based on P(VDF-TrFE)/BaTiO3 micropillars can be attributed to the enhanced piezoelectricity of the nanocomposite materials and the improved mechanical flexibility of the micropillar array under compression.】

为验证这一点，测量器件的P-E磁滞曲线。Figure 3d。最大极化增加【59】

介电常数可以反映介质材料在高压下的极化能力
Figure 3d的inset：
P(VDF-TrFE)/BaTiO3 的介电常数远大于P(VDF-TrFE)的介电常数。

压电耦合系数d33：反应了压电材料经机械形变转化为电信号的能力。P(VDF-TrFE)和P(VDF-TrFE)/BaTiO3 的d33分别为14.5和35.4 pC/N。

[All these results show the BaTiO3 nanoparticles significantly enhance the piezoelectric performance of the nanocomposite material]

Figure S9: P(VDF-TrFE)基底的傅立叶变换红外光谱(FTIR)光谱和XRD。可以看出P(VDF-TrFE)基底有高β相结晶度，根据【46,48】的研究，结晶相的P(VDF-TrFE)有证的压电特性，能高效的转换施加的压力，对压电性能也有贡献，增强电输出。【Figure S9 (Supporting Information) shows the fourier transform infrared spectroscopy (FTIR) spectrum and XRD results of P(VDF-TrFE) matrix, which indicated that the flexible P(VDF-TrFE) matrix has a high β phase crystallinity. According to the research of Lee et al.,[46,48] the crystallinephase P(VDF-TrFE) also exhibits positive piezoelectricity，which transfers the energy of the applied pressure efficiently and also contributes piezoelectricity to enhance the output.】

在压力下，压力均匀的分布在BT和P上，同时，BT的存在会增加P上的局部变形

Upon the application of stress, the piezoelectric potential is generated simultaneously inside the uniformly dispersed BT NPs and the crystalline P(VDF-TrFE), which will produce a
coupled giant piezoelectricity. Besides, the BaTiO3 NPs can also reinforce the local stress of the P(VDF-TrFE) matrix and induce larger local deformation of the polymer compared with the pure P(VDF-TrFE) film, which has been discussed by Zhang et a【30】

Figure S10：P(VDF-TrFE) micropillar array and nanocomposite P(VDF-TrFE)/BaTiO3 micropillar array的比较信息
分别为4.8V和13.2V，微柱结构也对于压电特性有贡献

为证明这一点，使用COMSOL软件包的有限元模拟法finite element method simulation来理论分析。Figure 3ef。

Figure S11：在相同压力下的位移。微柱有更大的位移94nm，而薄膜16nm。有更大的形变

低密度，高纵横比。
直径，高度和密度的影响在威力啊的工作中继续讨论。

Figure 4a-i：50N的压力下，不同负载电阻的输出电压，4a-ii：为功率密度，钟型结构与【65】中的讨论相符，3.9M $Ω\Omega$ 的负载电阻下，最大输出功率为12.7uW/ $cm^2$ 。
PENG-NG的感知性能在5-60N的压力线测试，Figure 4b展示了压力和输出电压之间的关系。
输出电压与压力近似成线性关系，斜率：nanocomposite micropillar array and the pristine P(VDF-TrFE) bulk film are 257.9
and 37.1 mV/N。
Figure 4c：压电纳米发电机具有良好的机械鲁棒性和稳定性，其输出电压在经过12000 s后只有轻微的波动。
inset展示了放大的释放和压缩时的峰值图

The stable performance can be attributed to the robust mechanical property of the nanocomposite structures under significant deformation and the full flexibility design of the entire structure

Figure 4d测试弯曲下的电输出特性
Figure 4e-i：在不同弯曲程度下的输出电压。

随着弯曲程度的增加，形变变大，内部电势增加，所以电压峰值增加【The peaks of the measured voltages were increased with the bending degree as the internal piezoelectric potential can be enhanced by the introduced strain.】

Figure 4e-ii：水平位移1-10mm下的电输出曲线
The results show outputs increased with a lower growing rate upon the nanogenerator was bending to a certain degree

Figure 4f：手指弯曲/释放下的电压，最大电压可达20-25V，足以点亮4位LCD屏幕，Movie S1。

It is well known that the generated output energy of nanogenerators is strongly dependent on the external mechanical stress, the size of the sensing area and some other factors, such as piezoelectric coefficient of synthetic materials and degree of electric poling.

好的客套话：制作工艺和有潜力用于未来的应用
Besides, the nanoimprinting
technique adopted here for fabricating the vertical- aligned nanocomposite pillar array is relatively reliable, low-cost, and quite efficient process in mass production 。The resultant PENGs with good flexibility and high piezoelectric output are promised to realize various practical self-powered sensing applications.

接下来展示了一些应用：
For potential utilization of the electricity generated from the nanogenerator, we showed some applications of the PENM-NG to power consumer electronics.

使用全波桥将交流电压转换为直流电压，使用10uf的电容临时存储电荷。
Figure 5a：
To provide an uninterrupted power to an electric device, a full-wave bridge was used to convert the alternating voltage generated by a PENM-NG to direct voltage, and then used a capacitor of 10 μF for temporary charge storage

Figure 5b：显示了在不同压/释放的频率下充电过程

在50Hz的压缩振动下，18s内，电容电压可达3.7v

Figure 5c是Figure 5b的局部放大图，展示了电容的充放电的循环过程
Figure 5c is the magnified view of apportioning in Figure 5b confirming the expected stepwise charging behavior from cyclic compressing of PENM-NG

In order to confirm the reproducibility cyclic charging and possibility of long term use, cyclic charging and discharging were conducted. Figure S12

Figure 5d:
连接到电子表上，
电压在5s内到达1.4v，在连续的压缩下，电压能保持在1.4v上。

也可用于瞬时大功率任务，比如为音乐播放器充电 Figure 5e 和Movie S3

Figure 5f 和Movie S4，能够直接点亮5个蓝色LED灯而不要额外的储能单元。

These applications prove that the efficiency and utility of P(VDF-TrFE)/BaTiO3 nanocomposite micropillar array based PENGs we proposed here would be valuable in powering commercial electronics

由于P(VDF-TrFE)/BaTiO3垂直排列的微柱结构，甚至能用于非接触模式下检测压力，比如气压
Because of the enhanced piezoelectricity and high sensitivity of the vertically well-aligned P(VDF-TrFE)/BaTiO3 micropillar array, the PENM-NG device could even be used for detecting the pressure on the noncontact-mode, such as air pressure

Figure 6a：将PENG-NG放在注射器内部，通过压活塞实现周期的压力，获得AC电压输出(Figure 6a and Movie S5, Supporting
Information)

产生的电输出不对称，主要是由于压和释放时的压力和比率不同。
The generated electricity output was not quite symmetric because the pressure and rate were different for compressing and releasing of the piston

Figure 6b：测量了器件在5-30ml不同空气体积下压缩的电输出。

电压从0.15v增加到1.15v

Figure 6c: 给出了压电电压振幅与空气压缩体积之间的曲线

插图显示了电压输出随压力改变。
The above results indicated that the flexible piezoelectric nanogenerator can be applied for pressure sensors for monitoring small pressure varies

可以固定在胸上检测呼吸，Figure 6d

图6e显示了深呼吸、喘气、吃力呼吸和正常呼吸模式的典型测量呼吸信号
Figure 6e shows the typically measured respiration signals for deepbreathing, gasping, labored breathing, and normal breathing modes

The curves of output graphs closely follow the actual respiration cycle in both pitch and magnitude, which validates the effectiveness of sensor used for reflecting the actual respiration cycle and different respiration mode.

This study indicated that the highly sensitive vertical well-aligned piezoelectrically enhanced nanocomposite micropillar array based nanogenerator can be applied as a wearable sensor for health monitoring.

结论

In conclusion, a high-performance flexible piezoelectric nanogenerator made of piezoelectrically enhanced nanocomposite micropillar array of BaTiO3 nanoparticles embedded into a highly crystalline P(VDF-TrFE) polymer via a reliable and scalable nanoimprinting process is presented.
The output voltage from the P(VDF-TrFE)/BaTiO3 micropillar array was thoroughly characterized under vertical compressive force and period bending deformation. The piezoelectric voltage of the PENM-NG device increases linearly with the input pressure and shows about 7.3 times higher value than pristine P(VDF-TrFE) film. The strong power-generating performance can be attributed to the enhanced piezoelectricity of the nanocomposite materials and the improved mechanical flexibility of the micropillar array under compression, which has been discussed by P–E loops test and COMSOL simulation. Under repeated mechanical impact, stable electricity was stably generated from the nanogenerator and used to drive electronic devices (such as LCD screen, arrays of blue LEDs connected in series, digital watch, and music player) to work continuously. Finally, the piezoelectrically enhanced nanocomposite micropillar array was successfully demonstrated as highly sensitive self-powered sensor work in a noncontact mode for detecting air pressure/flow. It also can be used as wearable sensors for measuring human vital signals including breathing, heart beating. Because of the distinctive features of high sensitivity, good stability, and high power-generating property, the proposed PENM-NG will have a wide potential application in fields of the smart clothes, medical sciences, and next-generation electronics.