Interfacial Engineering Importance of Bilayered ZnO Cathode Buffer on the Photovoltaic Performance of Inverted Organic Solar Cells.

Ambade, Rohan B,Ambade, Swapnil B,Mane, Rajaram S,Lee, Soo-Hyoung American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.15

<P>The role of cathode buffer layer (CBL) is crucial in determining the power conversion efficiency (PCE) of inverted organic solar cells (IOSCs). The hallmarks of a promising CBL include high transparency, ideal energy levels, and tendency to offer good interfacial contact with the organic bulk-heterojunction (BHJ) layers. Zinc oxide (ZnO), with its ability to form numerous morphologies in juxtaposition to its excellent electron affinity, solution processability, and good transparency is an ideal CBL material for IOSCs. Technically, when CBL is sandwiched between the BHJ active layer and the indium-tin-oxide (ITO) cathode, it performs two functions, namely, electron collection from the photoactive layer that is effectively carried out by morphologies like nanoparticles or nanoridges obtained by ZnO sol-gel (ZnO SG) method through an accumulation of individual nanoparticles and, second, transport of collected electrons toward the cathode, which is more effectively manifested by one-dimensional (1D) nanostructures like ZnO nanorods (ZnO NRs). This work presents the use of bilayered ZnO CBL in IOSCs of poly(3-hexylthiophene) (P3HT)/[6, 6]-phenyl-C60-butyric acid methyl ester (PCBM) to overcome the limitations offered by a conventionally used single layer CBL. We found that the PCE of IOSCs with an appropriate bilayer CBL comprising of ZnO NRs/ZnO SG is 18.21% higher than those containing ZnO SG/ZnO NRs. We believe that, in bilayer ZnO NRs/ZnO SG, ZnO SG collects electrons effectively from photoactive layer while ZnO NRs transport them further to ITO resulting significant increase in the photocurrent to achieve highest PCE of 3.70%. The enhancement in performance was obtained through improved interfacial engineering, enhanced electrical properties, and reduced surface/bulk defects in bilayer ZnO NRs/ZnO SG. This study demonstrates that the novel bilayer ZnO CBL approach of electron collection/transport would overcome crucial interfacial recombination issues and contribute in enhancing PCE of IOSCs.</P>

Polythiophene infiltrated TiO₂ nanotubes as high-performance supercapacitor electrodes

Ambade, Rohan B.,Ambade, Swapnil B.,Shrestha, Nabeen K.,Nah, Yoon-Chae,Han, Sung-Hwan,Lee, Wonjoo,Lee, Soo-Hyoung The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.23

<P>We report exceptional electrochemical specific capacitance (640 F g<SUP>−1</SUP>) for polythiophene (PTh) infiltrated into TiO<SUB>2</SUB> nanotubes (TNTs) by a controlled electropolymerization route. The resulting PTh–TNTs also exhibit excellent electrochemical behavior with long-term stability. This reproducible and superior performance of PTh–TNT electrodes makes them attractive candidates for energy storage.</P> <P>Graphic Abstract</P><P>An exceptional electrochemical capacitance of 640 F g<SUP>−1</SUP> with high conductivity and long term stability was obtained for electropolymerized polythiophene infiltrated into the matrix of highly ordered TiO<SUB>2</SUB> nanotubes. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc00065f'> </P>

Development of highly transparent seedless ZnO nanorods engineered for inverted polymer solar cells.

Ambade, Swapnil B,Ambade, Rohan B,Lee, Wonjoo,Mane, Rajaram S,Yoon, Sung Cheol,Lee, Soo-Hyoung RSC Pub 2014 Nanoscale Vol.6 No.20

<P>This work reports on inverted polymer solar cells (IPSCs) based on highly transparent (>95%), hydrophobic, seedless ZnO nanorods (NRs) as cathode buffers with extremely enhanced electrical characteristics. The transparent NR suspension with stability for more than a year is achieved by adding a small amount of 2-(2-methoxyethoxy) acetic acid (MEA). The ability of the stable nanorod suspension to easily spin-coat is certainly an advance to the fabrication of films over large areas and to replace the conventional seeding method to grow one-dimensional nanostructures for use in optoelectronic devices. We observe a strong correlation between the photovoltaic performance and the transparency of ZnO NRs. IPSCs using poly-3-hexylthiophene (P3HT) and [6,6]-phenyl C60 butyric acid methyl ester (PCBM) mixtures in the active layer and transparent (MEA-capped) ZnO NRs as cathode buffers exhibit a power conversion efficiency of 3.24% under simulated AM 1.5G, 100 mW cm(-2) illumination.</P>

Triple-tyrosine kinase inhibition attenuates pulmonary arterial hypertension and neointimal formation

Ambade, Anjira S.,Jung, Birgit,Lee, Dongwon,Doods, Henri,Wu, Dongmei Elsevier 2019 Translational research Vol.203 No.-

<P>The present study examined the effects of simultaneous inhibition of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) receptor signaling with BIBF1000, a novel triple tyrosine kinase inhibitor on preventing and reversing the progression of severe pulmonary arterial hypertension (PAH) in an experimental model in rats. Left pneumonectomized male Wistar rats were injected with monocrotaline to induce PAH. Treatment with BIBF1000 from day 1 to day 21 after monocrotaline injection attenuated PAH development, as evidenced by lower values for pulmonary artery pressure (mPAP), right ventricular pressure (RVSP), pulmonary arterial neointimal formation, and the ratio of right ventricular weight to left ventricular and septum weight [RV/(LV+S)] on day 21 compared to control rats. Treatment with BIBF1000 from day 21 to day 42 after monocrotaline injection reversed established PAH as shown by normalized values for mPAP and RVSP, RV/(LV+S) ratio, pulmonary arterial occlusion scores, levels of heart and lung fibrosis, as well as improved survival. Treatment with BIBF1000 reduced inflammatory cell recruitment in bronchoalveolar lavage and lung tissues, reduced CD-68 positive macrophages and expression of proliferating cell nuclear antigen in the perivascular areas, and reduced TNF-α and growth factor productions, and inhibited the phosphorylation of AKT and GSK3β in lungs. In addition, BIBF1000 inhibited pulmonary artery smooth muscle cells migration and proliferation from rat pulmonary artery explant cultures. Simultaneous inhibition of VEGF, PDGF, and FGF receptor signaling by BIBF1000 prevents and reverses the progression of severe pulmonary arterial hypertension and vascular remodeling in this experimental model.</P>

Controlled growth of polythiophene nanofibers in TiO2 nanotube arrays for supercapacitor applications

Ambade, R.,Ambade, S.,Shrestha, N.,Salunkhe, R.,Lee, W.,Bagde, S.,Kim, J.,Stadler, F.,Yamauchi, Y.,Lee, S. H. Royal Society of Chemistry 2017 Journal of materials chemistry. A, Materials for e Vol.5 No.1

<P>One-dimensional (1D) nanostructured materials have attracted intense interest because they are superior for applications when compared to their bulk counterparts, owing to their unique and fascinating properties. We thus demonstrate the development of conducting 1D polythiophene (PTh) nanofibers in hollow TiO2 nanotube arrays (TNTs) by controlling nucleation and growth during the electropolymerization of the thiophene monomer. The progression of nanofiber (NF) formation in the hollow interiors of the TNTs follows a three-dimensional instantaneous nucleation and growth mode, in which the polymer grows at a rate that does not allow for the build-up of the polymer on new polymerization sites, but only on existing ones. The formation of highly conductive dienes of PTh is confirmed, with increased conjugation in PTh NFs grown in the confined matrix of TNTs. These 1D PTh-TNT NFs show potential as a promising supercapacitor electrode material, exhibiting a high specific capacitance of 1052 F g(-1), which clearly highlights their importance as potential next-generation charge storage entities.</P>

Kinetically controlled low-temperature solution-processed mesoporous rutile TiO₂ for high performance lithium-ion batteries

Ambade, Rohan B.,Koh, Ki Hwan,Ambade, Swapnil B.,Eom, Wonsik,Noh, Sung Hyun,Koo, Chong Min,Kim, Seong Hun,Han, Tae Hee Elsevier 2019 Journal of industrial and engineering chemistry Vol.80 No.-

<P><B>Abstract</B></P> <P>Solution-processed nanostructured mesoporous rutile phase titanium dioxides (TiO<SUB>2</SUB>) are a fascinating class of materials for energy applications owing to their remarkable properties, including thermal stability. The unique lattice structure of rutile TiO<SUB>2</SUB> (R-TiO<SUB>2</SUB>) leads to multifaceted physicochemical properties, which influence its performances. We here report the preparation of mesoporous R-TiO<SUB>2</SUB> via a simple and scalable solution process at a low temperature (<50°C). Kinetically controlled synthesis of mesoporous R-TiO<SUB>2</SUB> with three-dimensional hierarchical sea-urchin-like morphology containing populous one-dimensional nanorods are prepared from the precipitates of our cocktail-like precursor solutions of TiCl<SUB>4</SUB> and CH<SUB>4</SUB>N<SUB>2</SUB>S. The mesoporous R-TiO<SUB>2</SUB> annealed at 300°C possessing a large surface area manifests excellent energy storage behavior, with a high capacity of 457mAhg<SUP>−1</SUP> for the first discharge cycle, at a current density of 0.2 C in the potential range of 1–3V, as well as a high reversible charge–discharge capacity, high rate performance, and excellent cycling stability for lithium-ion batteries. We anticipate our straightforward wet-chemical method to advance the development of mesoporous TiO<SUB>2</SUB> as a promising candidate for high-performance energy storage and other energy applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Kinetically controlled mesoporous rutile TiO<SUB>2</SUB> was synthesized by the facile wet-chemical method at a reaction temperature below 50°C. </LI> <LI> Synthesized rutile TiO<SUB>2</SUB> exhibited exceptional phase stability even after high-temperature annealing at 1000°C. </LI> <LI> The rutile TiO<SUB>2</SUB> after thermal annealing was successfully used as an anode material for Li-ion battery. </LI> <LI> The mesoporous rutile TiO<SUB>2</SUB> with high surface area exhibited a significantly high capacity, high rate performance, and excellent cycling stability for Li-ion battery. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A simple kinetically controlled low-temperature mesoporous rutile TiO<SUB>2</SUB> (R-TiO<SUB>2</SUB>) is successfully developed as high-performance anode material for a Li-ion battery (LIB). Effect of the morphology, properties and on the LIB performance of R-TiO<SUB>2</SUB> at different annealing temperatures is investigated. The mesoporous R-TiO<SUB>2</SUB>-300 with large surface area manifested excellent LIB energy storage behavior, with a high capacity of 457mAhg<SUP>−1</SUP> at a current density of 0.2 C, as well as a high reversible charge–discharge capacity, high rate performance, and excellent cycling stability for LIBs.</P> <P>[DISPLAY OMISSION]</P>

Performance enhancement in inverted solar cells by interfacial modification of ZnO nanoparticle buffer layer.

Ambade, Swapnil B,Ambade, Rohan B,Kim, Seojin,Park, Hanok,Yoo, Dong Jin,Leel, Soo-Hyoung American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.11

<P>Polymer solar cells (PSCs) have attracted increasing attention in recent years. The rapid progress and mounting interest suggest the feasibility of PSC commercialization. However, critical issues such as stability and the weak nature of their interfaces posses quite a challenge. In the context of improving stability, PSCs with inverted geometry consising of inorganic oxide layer acting as an n-buffer offer quite the panacea. Zinc oxide (ZnO) is one of the most preferred semiconducting wide band gap oxides as an efficient cathode layer that effectively extracts and transports photoelectrons from the acceptor to the conducting indium-doped tin oxide (ITO) due to its high conductivity and transparency. However, the existence of a back charge transfer from metal oxides to electron-donating conjugated polymer and poor contact with the bulk heterojunction (BHJ) active layer results in serious interfacial recombination and leads to relatively low photovoltaic performance. One approach to improving the performance and charge selectivity of these types of inverted devices consists of modifying the interface between the inorganic metal oxide (e.g., ZnO) and organic active layer using a sub-monolayer of interfacial materials (e.g., functional dyes). In this work, we demonstrate that the photovoltaic parameters of inverted solar cells comprising a thin overlayer of functional dyes over ZnO nanoparticle as an n-buffer layer are highly influenced by the anchoring groups they possess. While an inverted PSC containing an n-buffer of only ZnO exhibited an overall power conversion efficiency (PCE) of 2.87%, the devices with an interlayer of dyes containing functional cyano-carboxylic, cyano-cyano, and carboxylic groups exhibited PCE of 3.52%, 3.39%, and 3.21%, respectively, due to increased forward charge collection resulting from enhanced electronic coupling between the ZnO and BHJ active layers.</P>

Low-Temperature Solution-Processed Thiophene-Sulfur-Doped Planar ZnO Nanorods as Electron-Transporting Layers for Enhanced Performance of Organic Solar Cells

Ambade, Swapnil B.,Ambade, Rohan B.,Bagde, Sushil S.,Eom, Seung Hun,Mane, Rajaram S.,Shin, Won Suk,Lee, Soo-Hyoung American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.4

<P>1-D ZnO represents a fascinating class of nanostructures that are significant to optoelectronics. In this work, we investigated the use of an eco-friendly, metal free in situ doping through a pure thiophene-sulfur (5) on low temperature processed (<95 degrees C) and annealed (<170 degrees C), planar 1-D ZnO nanorods (ZnRs) spin-coated as a hole blocking and electron transporting layer (ETL) for inverted organic solar cells (iOSCs). The TEM, HRTEM, XPS, FT-IR, EDS and Raman studies clearly reveal that the thiophene-S (Thi-S) atom is incorporated on planar ZnRs. The investigations in electrical properties suggest the enhancement in conductivity after Thi-S doping on 1-D ZnRs. The iOSCs of poly.(3-hexylthiophene-2,5-diyl) and phenyl-C-61-butyric acid methyl ester (P3HT: PC60BM) photoactive layer containing thiophene-S doped planar ZnRs (Thi-S-PZnRs) as ETL exhibits power conversion efficiency (PCE) of 3.68% under simulated AM 1.5 G, 100 mW cm(-2) illumination. The similar to 47% enhancement in PCE compared with pristine planar ZnRs (PCE = 2.38%) ETL is attributed to a combination of desirable energy level alignment, morphological modification, increased conductivity and doping effect. The universality of Thi-S-PZnRs ETL is demonstrated by the highest PCE of 8.15% in contrast to 6.50% exhibited by the iOSCs of ZnRs ETL for the photoactive layer comprising of poly[4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b;4,5-b]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] : phenyl-C71-butyric acid methyl ester (PTB7-Th: PCB71M). This enhancement in PCE is observed to be driven mainly through improved photovoltaic parameters like fill factor (ff) as well as photocurrent density (J(sc)), which are assigned to increased conductivity, exciton dissociation, and effective charge extraction, while; better ohmic contact, reduced charge recombination, and low leakage current density resulted in increased Voc.</P>

Flexible-wire shaped all-solid-state supercapacitors based on facile electropolymerization of polythiophene with ultra-high energy density

Ambade, Rohan B.,Ambade, Swapnil B.,Salunkhe, Rahul R.,Malgras, Victor,Jin, Sung-Ho,Yamauchi, Yusuke,Lee, Soo-Hyoung The Royal Society of Chemistry 2016 Journal of materials chemistry. A, Materials for e Vol.4 No.19

<P>The new generation of miniaturized energy storage devices offers high energy and power densities and is compatible with flexible, portable, or wearable textile electronics which are currently in great demand. Here, we demonstrate the successful development of flexible, wire shaped (f-WS) all-solid-state symmetric supercapacitors (SCs) based on a facile electropolymerization of polythiophene (e-PTh) on titania (Ti) wire. The f-WS all-solid-state symmetric SCs, exhibiting high electrochemical performance, are fabricated by slightly intertwining two similar e-PTh electrodes to form both the cathode and anode which are then individually coated with a thin layer of H2SO4-PVA gel, acting both as electrolyte and as separator. The optimized devices (∼1.5 cm long), based on e-PTh/Ti wire show a high capacitive performance (1357.31 mF g<SUP>−1</SUP>or 71.84 mF cm<SUP>−2</SUP>) and an extremely high energy density (23.11 μW h cm<SUP>−2</SUP>) at a power density of 90.44 μW cm<SUP>−2</SUP>using an operational potential window of 1.8 V, which is beneficial for applications requiring high energy and power. The robust f-WS all-solid-state symmetric SCs also exhibit excellent mechanical flexibility with minimal change in capacitance upon bending at 360°. Furthermore, the SCs were implemented in the textile of a wearable/portable electronic device using a conventional weaving method, thus demonstrating a high potential for next-generation wearable textile electronic applications.</P>

Co-functionalized organic/inorganic hybrid ZnO nanorods as electron transporting layers for inverted organic solar cells

Ambade, S.,Ambade, R.,Eom, S.,Baek, M. J.,Bagde, S.,Mane, R.,Lee, S. H. Royal Society of Chemistry 2016 Nanoscale Vol.8 No.9

<P>In an unprecedented attempt, we present an interesting approach of coupling solution processed ZnO planar nanorods (NRs) by an organic small molecule (SM) with a strong electron withdrawing cyano moiety and the carboxylic group as binding sites by a facile co-functionalization approach. Direct functionalization by SMs (SM-ZnO NRs) leads to higher aggregation owing to the weaker solubility of SMs in solutions of ZnO NRs dispersed in chlorobenzene (CB). A prior addition of organic 2-(2-methoxyethoxy) acetic acid (MEA) over ZnO NRs not only inhibits aggregation of SMs over ZnO NRs, but also provides enough sites for the SM to strongly couple with the ZnO NRs to yield transparent SM-MEA-ZnO NRs hybrids that exhibited excellent capability as electron transporting layers (ETLs) in inverted organic solar cells (iOSCs) of P3HT:PC60BM bulk-heterojunction (BHJ) photoactive layers. A strongly coupled SM-MEA-ZnO NR hybrid reduces the series resistance by enhancing the interfacial area and tunes the energy level alignment at the interface between the (indium-doped tin oxide, ITO) cathode and BHJ photoactive layers. A significant enhancement in power conversion efficiency (PCE) was achieved for iOSCs comprising ETLs of SM-MEA-ZnO NRs (3.64%) advancing from 0.9% for pristine ZnO NRs, while the iOSCs of aggregated SM-ZnO NRs ETL exhibited a much lower PCE of 2.6%, thus demonstrating the potential of the co-functionalization approach. The superiority of the co-functionalized SM-MEA-ZnO NRs ETL is also evident from the highest PCE of 7.38% obtained for the iOSCs comprising BHJ of PTB7-Th: PC60BM compared with extremely poor 0.05% for non-functionalized ZnO NRs.</P>