Enhancing the output performance of hybrid nanogenerators based on Al-doped BaTiO₃ composite films: a self-powered utility system for portable electronics

Dudem, Bhaskar,Bharat, L. Krishna,Patnam, Harishkumarreddy,Mule, Anki Reddy,Yu, Jae Su The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.33

<P>Enhancing the output performance of nanogenerators using composite films consisting of a piezoelectric material embedded into polymers has gained much attention over the last few years. Such composite films can provide a high surface charge density and dielectric permittivity, which can further efficiently enhance the performance of nanogenerators. We, for the first time, employed aluminum (Al)-doped barium titanate (BaTiO3; ABTO) particles to enhance the performance of nanogenerators. These ABTO particles were synthesized <I>via</I> a solid-state technique, and the effect of Al dopant concentration on their crystallinity and ferroelectric properties was systematically investigated. However, the BTO particles with 2% Al dopant concentration exhibited a high remnant polarization and piezoelectric coefficient, and they were further employed to efficiently enhance the output performance of the hybrid piezo/triboelectric nanogenerators. For this, these ABTO particles were first mixed with polydimethylsiloxane (PDMS) to prepare a composite film. Next, the ABTO/PDMS composite film was employed as a piezoelectric material and triboelectric material of the hybrid nanogenerator (HNG) and exhibited a high output performance owing to their synergetic effects. In addition, the influence of the surface roughness of the composite film on the performance of the HNG was also investigated and optimized. Consequently, the HNG device with the rough surface ABTO/PDMS composite film exhibited maximal open-circuit voltage, short-circuit current, and power density values of ∼945 V, ∼59.8 μA, and ∼42.4 W m<SUP>−2</SUP>, respectively. For practical device application, the stable and high electrical power generated from the HNG device was employed to light several light-emitting diodes and power portable electronic devices.</P>

Highly-flexible piezoelectric nanogenerators with silver nanowires and barium titanate embedded composite films for mechanical energy harvesting

Dudem, Bhaskar,Kim, Dong Hyun,Bharat, L. Krishna,Yu, Jae Su Elsevier 2018 APPLIED ENERGY Vol.230 No.-

<P><B>Abstract</B></P> <P>Piezoelectric nanogenerators (PNGs) is one of the promising technologies to convert mechanical energies into electricity for driving various mobile/portable electronic devices. Generally, the electrical output performance of PNGs is enhanced by electrical poling or annealing treatment, which involves high voltage and temperature techniques. Herein, we successfully demonstrated a flexible PNG designed by the barium titanate embedded polyvinylidene difluoride (i.e., BaTiO<SUB>3</SUB>/PVDF) composite film and attained a significant output performance with avoiding electrical poling process. These barium titanate micro stone-like architectures (BTO-MSs) were synthesized by a facile, eco-friendly, and cost-effective solid-state reaction. In addition, the output performance of PNG is further improved by dispersing the silver nanowires (Ag-NWs) as a conducting supplement filler along with the BTO-MSs into the PVDF matrix. Resultantly, the PNG with Ag-NWs/BTO/PVDF composite film exhibited a high open-circuit voltage (V<SUB>OC</SUB>) of ∼ 14 V and short-circuit current (I<SUB>SC</SUB>) of ∼ 0.96 μA compared to the PNG with only BTO/PVDF (V<SUB>OC</SUB>/I<SUB>SC</SUB> ∼ 11 V/0.78 μA) upon the application of a low pushing force of 3 N, cyclic pushing-releasing frequency of 5 Hz. Additionally, the effect of external load resistance, pushing force, and frequency on the electrical output performance of PNGs was investigated, including its mechanical stability and durability. Finally, an optimized PNG was employed to efficiently harvest/detect the mechanical energy from automotive vehicle motion and human body movements.</P> <P><B>Highlights</B></P> <P> <UL> <LI> BTO was synthesized by a facile, eco-friendly, and cost-effective solid-state reaction. </LI> <LI> Performance of PNG is improved by Ag-NWs and BTO embadded composites. </LI> <LI> Particularly, the risky and high-field poling process was avoided. </LI> <LI> The PNG is employed to effectively harvest the energy from automotive vehicle motions. </LI> <LI> The flexibility of PNG was also examined and used to detect human hand movement. </LI> </UL> </P>

Wearable and durable triboelectric nanogenerators via polyaniline coated cotton textiles as a movement sensor and self-powered system

Dudem, Bhaskar,Mule, Anki Reddy,Patnam, Harishkumar Reddy,Yu, Jae Su Elsevier 2019 Nano energy Vol.55 No.-

<P><B>Abstract</B></P> <P>Recently, wearable and flexible triboelectric nanogenerators (TENGs) have attracted tremendous research interest owing to their ability to harvest the energy from working environments and been further utilized to power various portable electronics. In this regard, for the first time, we report a polyaniline (PANI)-based flexible and wearable TENG in low-processing cost with superior electrical performance and durability. The cotton textile with good flexibility and intertwined micro-fibrous network is utilized as a scaffold to deposit PANI by a facile, cost-effective and low-temperature in-situ polymerization method. Moreover, the fibrous textured cotton textile can also offer high surface roughness, which enhances the output performance of TENG. Herein, this PANI coated worn-out cotton textile (PANI@WCT) is employed as a positive triboelectric material and electrode to design a TENG. The PANI@WCT produced at the deposition time of 20 h is realized as an optimal sample to attain high output performance. The electrical stability and mechanical durability of PANI@WCT-based TENG (PW-TENG) are also examined under long-term cyclic compression operations and various mechanical deformation cycles. Furthermore, the PANI@WCT has a potency in constructing vertical contact-separation dual-electrode mode TENG as well as it also serves as a single-electrode mode. So, the electrical output performance of single-electrode mode PW-TENG is also analyzed while it makes a contact with various materials available in our daily life. Finally, to demonstrate the practical applications of PW-TENG, the generated power is used to drive various portable electronics for wearable electronic applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We reported a polyaniline-based flexible and wearable TENG in low-processing cost with superior performance. </LI> <LI> It exhibited a stable electrical performance even after long-term compression and mechanical deformation operations. </LI> <LI> PANI@WCT has a potency in constructing the dual-electrode mode as well as a single-electrode mode TENG. </LI> <LI> Finally, the PW-TENG was employed to drive various portable electronics for wearable electronic applications. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Improved light harvesting efficiency of semitransparent organic solar cells enabled by broadband/omnidirectional subwavelength antireflective architectures

Dudem, Bhaskar,Jung, Jae Woong,Yu, Jae Su The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.30

<P>We report organic solar cells (OSCs) with subwavelength architectured polydimethylsiloxane (SWA-PDMS) as an antireflective (AR) layer on a glass substrate for not only enhancing the efficiency but also increasing the transparency of the devices. These subwavelength architectures (SWAs) on PDMS layers are fabricated using a soft imprint lithography technique <I>via</I> an anodic aluminum oxide mold. The effect of optical characteristics of SWA-PDMS with respect to the period and diameter of SWAs, along with the theoretical analysis using rigorous coupled-wave analysis simulation, is investigated. Consequently, the SWA-PDMS/glass with a period and diameter of 125 nm and 80 nm, respectively, is obtained as the optimal sample, exhibiting the highest average transmittance (<I>T</I>avg) of ∼95.2%, which is much higher compared to that of bare glass (<I>T</I>avg ∼92.08%). By employing the optimal SWA-PDMS on the glass surface of opaque and semitransparent OSCs as an AR layer, their power conversion efficiency is improved from 8.67 to 10.59% and 7.07 to 8.52%, respectively. Additionally, the average visible transmittance (AVT) of the semitransparent OSC is increased from 23.0 to 26.2% with significantly improved color coordinates as the AR layer is employed. Also, the OSCs with SWA-PDMS having a relatively high hydrophobic nature exhibit a stable performance in the ambient environment.</P>

Enhanced Performance of Microarchitectured PTFE-Based Triboelectric Nanogenerator via Simple Thermal Imprinting Lithography for Self-Powered Electronics

Dudem, Bhaskar,Kim, Dong Hyun,Mule, Anki Reddy,Yu, Jae Su American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.28

<P>Triboelectric nanogenerator (TENG) technology is an emerging field to harvest various kinds of mechanical energies available in our living environment. Nowadays, for industrial and large-scale area applications, developing the TENG with low device processing cost and high electrical output is a major issue to be resolved. Herein, we designed a TENG with low cost by employing the microgrooved architectured (MGA)-poly(tetrafluoroethylene) (PTFE; Teflon) and aluminum as triboelectric materials with opposite tendencies. Moreover, the MGA-PTFE was fabricated by a single-step, facile, and cost-effective thermal imprinting lithography technique via micropyramidal textured silicon as a master mold, fabricated by a wet-chemical etching method. Therefore, designing the TENG device by following these techniques can definitely reduce its manufacturing cost. Additionally, the electrical output of TENG was enhanced by adjusting the imprinting parameters of MGA-PTFE. Consequently, the MGA-PTFE was optimized at an imprinting pressure and temperature of 5 MPa and 280 °C, respectively. Thus, the TENG with an optimal MGA-PTFE polymer exhibited the highest electrical output. A robustness test of TENG was also performed, and its output power was used to drive light-emitting diodes and portable electronic devices. Finally, the real application of TENG was also examined by employing it as a smart floor and object-falling detector.</P> [FIG OMISSION]</BR>

Broadband and wide-angle antireflective characteristics of nanoporous anodic alumina films for silicon-based optoelectronic applications

Dudem, B.,Leem, J. W.,Choi, M.,Yu, J. S. Springer Science + Business Media 2015 Applied physics. B, Lasers and optics Vol.118 No.3

Hybrid Energy Cell with Hierarchical Nano/Micro-Architectured Polymer Film to Harvest Mechanical, Solar, and Wind Energies Individually/Simultaneously

Dudem, Bhaskar,Ko, Yeong Hwan,Leem, Jung Woo,Lim, Joo Ho,Yu, Jae Su American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.44

<P>We report the creation of hybrid energy cells based on hierarchical nano/micro-architectured polydimethylsiloxane (HNMA-PDMS) films With multifunctionality to simultaneously harvest mechanical, solar, and wind energies. These films consist of nano/micro dual-scale architectures (i.e., nanonipples on inverted micropyramidal arrays) on the PDMS surface. The HNMA-PDMS is replicable by facile and cost-effective soft imprint lithography using a nanoporous anodic alumina oxide film formed on the micropyramidal-structured silicon substrate. The HNMA-PDMS film plays multifunctional roles as a triboelectric layer in nanogenerators and an antireflection layer for dye-sensitized solar cells (DSSCs); as well as a self-cleaning surface. This film is employed in triboelectric nanogenerator (TENG) devices, fabricated by laminating it on indium tin oxide-coated polyethylene terephthalate (ITO/PET) as a bottom electrode. The-large, effective contact area that emerged from the densely packed hierarchical nano/micro-architectures of the PDMS film leads to the enhancement of TENG device performance. Moreover, the HNMA-PDMS/ITO/PET, with a high transmittance of >90%, also results in highly transparent TENG devices. By, placing the HNMA-PDMS/ITO/PET, where the ITO/PET is coated with zinc oxide nano-wires, as the top glass substrate of DSSCs; the device is able to add the functionality Of TENG devices, thus creating a hybrid energy cell. The hybrid energy cell can successfully convert mechanical, solar, and wind energies into electricity, simultaneously or independently. To specify the device performance, the effects of external pushing frequency and load resistance on the output of TENG devices are also analyzed, including the photovoltaic performance of the hybrid energy cells.</P>

Triboelectric nanogenerators with gold-thin-film-coated conductive textile as floating electrode for scavenging wind energy

Dudem, B.,Kim, D. H.,Yu, J. S. Springer Science + Business Media 2018 Nano research Vol.11 No.1

<P>We report triboelectric nanogenerators (TENGs) composed of a flexible and cost-effective gold-coated conductive textile (CT) to convert wind energy into electricity. The Au-coated CT is employed because of its high surface roughness resulting from Au nanodots distributed on microsized fibers. Thus, the Au-coated CT with nano/microarchitecture plays an important role in enhancing the effective contact area as well as the output performance of the TENG. Moreover, the surface roughness of the Au-coated CT is controlled by adjusting the Au thermal deposition time or tailoring the diameter of the Au nanodots. At an applied wind speed of 10 m.s(-1), a wind-based TENG (W-TENG) with dimensions of 75 mm x 12 mm x 25 mm produces an open-circuit voltage (V-OC) of similar to 39 V and a short-circuit current (I-SC) of similar to 3 mu A by using the airflow-induced vibrations of an optimized Au-coated CT between two flat polydimethylsiloxane (PDMS) layers. To further specify the device performance, the electric output of the W-TENG is analyzed by varying several parameters such as the distance between the PDMS layer and Au-coated CT, applied wind speed, external load resistance, and surface roughness of the PDMS layers. Introducing an inverse micropyramid architecture on the PDMS layers further improves the output performance of the W-TENG, which exhibits the highest V-OC (similar to 49 V) and I-SC (similar to 5 mu A) values at an applied wind speed of 6.8 m.s(-1). Additionally, the reliability of the W-TENG is also tested by measuring its output current during long-term cyclic operation. Furthermore, the rectified output signals observed by the W-TENG device are used as a direct power source to light 45 green commercial light-emitting diodes connected in series and also to charge capacitors (100 and 4.7 mu F). Finally, the output performance of the W-TENG device in an actual windy situation is also investigated.</P>

CH3NH3PbI3planar perovskite solar cells with antireflection and self-cleaning function layers

Dudem, Bhaskar,Heo, Jin Hyuck,Leem, Jung Woo,Yu, Jae Su,Im, Sang Hyuk The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.20

<P>We report CH3NH3PbI3planar perovskite solar cells with multifunctional inverted micro-pyramidal structured (IMPS) polydimethylsiloxane (PDMS) antireflection (AR) layers for enhancing the device efficiency. These IMPS-PDMS films were fabricated<I>via</I>a facile and cost-effective soft lithography using micro-pyramidal structured silicon (Si) master molds formed by alkaline anisotropic wet-etching treatment of (100)-oriented monocrystalline Si substrates. The IMPS-PDMS laminated on the bare glass (<I>i.e.</I>, IMPS-PDMS/glass) exhibited a higher solar weighted transmittance (<I>T</I>SW) value of ∼95.2% (or the lowest solar weighted reflectance (<I>R</I>SW) of ∼4.7%) than those of the bare glass and flat-PDMS/glass,<I>i.e.</I>,<I>T</I>SW/<I>R</I>SW∼ 90.7/9.1 and 91.5/8.2%, respectively. Additionally, it showed a much higher average haze ratio (<I>H</I>A) value of ∼93.1% compared to the bare glass and flat-PDMS/glass (<I>i.e.</I>,<I>H</I>A∼ 1.6 and 2.8%, respectively). By employing the IMPS-PDMS onto the outer surface of CH3NH3PbI3planar perovskite solar cells as an AR layer, an improved short-circuit current density (<I>J</I>sc) value of 21.25 mA cm<SUP>−2</SUP>was obtained, as compared to the reference device and the device with flat-PDMS (<I>i.e.</I>,<I>J</I>sc= 20.57 and 20.87 mA cm<SUP>−2</SUP>, respectively), while showing the almost same<I>V</I>ocand FF values as those of the reference device. As a result, the power conversion efficiency was improved from 17.17 and 17.42% for the reference and flat-PDMS devices, respectively, to 17.74% for the IMPS-PDMS device. Also, the fluorooctyltrichlorosilane-treated IMPS-PDMS surface revealed a superhydrophobic behavior with a water contact angle of ∼150° which is useful for self-cleaning applications in outdoor environments.</P>

Nanopillar-array architectured PDMS-based triboelectric nanogenerator integrated with a windmill model for effective wind energy harvesting

Dudem, Bhaskar,Huynh, Nghia Dinh,Kim, Wook,Kim, Dong Hyun,Hwang, Hee Jae,Choi, Dukhyun,Yu, Jae Su Elsevier 2017 Nano energy Vol.42 No.-

<P><B>Abstract</B></P> <P>Triboelectric nanogenerator (TENG) is an up-and-coming technology that functions based on the triboelectrification and electrostatic induction to generate the electricity from various mechanical energy sources. However, the practical applications still demand a significant improvement of the TENG output performance, so the optimization of key factors such as triboelectric material selectivity, nanostructure-like morphology, and surface contact area is very crucial. Here, we reported a TENG based on nanopillar-array architectured polydimethylsiloxane (NpA-PDMS) layers with simple and cost-effective fabrication process, high output performance, and long-term stability. We mainly focused on improving the output performance of TENG by optimizing the structural dimensions of nanopillar architectures (NpAs) distributed on the surface of PDMS. The effect of output performance of TENG by varying the period and diameter of NpAs on the surface of PDMS was theoretically and experimentally investigated. For theoretical study, we considered the NpA-PDMS as a viscoelastic material. From this simulation, we calculated the contact stress for NpA-PDMS layers and compared the behaviors by considering the contact area and stress together (i.e., the product of contact area and stress, called as a contact force). Surprisingly, the calculated results were well matched with the experimental data. And, an optimal NpA-PDMS with the period and diameter of 125nm and 60nm, respectively, was formed. Thus, the TENG with the optimal NpA-PDMS exhibited the open-circuit voltage (<I>V</I> <SUB>OC</SUB>) and short-circuit current (<I>I</I> <SUB>SC</SUB>) values of ~ 568V and ~ 25.6μA, respectively, under 10N of pushing force and 5Hz of pushing frequency. Additionally, the enduringness test of the TENG device was also conducted to confirm its mechanical stability and durability. Finally, for a real application, the optimized TENG device was incorporated with a windmill system to effectively harvest the wind energy available in indoor and outdoor environments. This windmill system effectively harvested the wind energy, exhibiting the <I>V</I> <SUB>OC</SUB> and <I>I</I> <SUB>SC</SUB> values of ~ 200V and ~ 24µA, respectively, at the wind speed of 14–15m/s.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We propose TENGs based on NpA-PDMS layers. </LI> <LI> The output performance of TENG by varying the structural dimensions of NpAs-PDMS was investigated. </LI> <LI> The optimum dimension of surface structure was determined by effective contact force. </LI> <LI> The TENG was incorporated with the windmill system to effectively harvest wind energy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>