Browsing by Author "Karapala, Vamsi Krishna"

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Chlorinated Carbon-Bridged and Silicon-Bridged Carbazole-Based Nonfullerene Acceptors Manifest Synergistic Enhancement in Ternary Organic Solar Cell with Efficiency over 15%
(1970-01-01)
Chen, Tsung-Wei
;
Yu, Jun-Yan
;
Lin, You-Wei
;
Peng, Shih-Hao
;
Wu, Shang-Hsuan
Herein, two novel nonfullerene acceptors (NFAs), DTCC-4Cl and DTSiC-4Cl, are synthesized by end-capping dithienocyclopentacarbazole (DTCC) and dithieno-silolocarbazole (DTSiC) cores with chlorinated IC (2Cl-IC) units, respectively. With the better-known advantage of having the extraordinary sigma*-pi* conjugation of silole unit embedded in the DTSiC core, DTSiC-4Cl manifests upshifted lowest unoccupied molecular orbital (LUMO), blue-shifted absorption, and increased pi-pi interaction in comparison with DTCC-4Cl. Furthermore, to elucidate the effect of bridging atoms on the photovoltaic performance, T1 is selected as the polymer donor to be blended with DTCC-4Cl and DTSiC-4Cl. T1:DTCC-4Cl-based devices exhibit a fine power conversion efficiency (PCE) of 14.43% and T1:DTSiC-4Cl-based devices exhibit a comparable PCE of 14.46%. Interestingly, the T1:DTSiC-4Cl-based devices demonstrate an additive-free feature, which is worthy of further applications. From the perspective of constructing high-performance ternary devices, DTCC-4Cl is expected to possess excellent compatibility with DTSiC-4Cl owing to its structural similarity. As anticipated, the ternary T1:DTSiC-4Cl:DTCC-4Cl-based device outperforms the binary T1:DTCC-4Cl and T1:DTSiC-4Cl-based devices, affording a decent PCE of 15.04% with aV(OC)of 0.97 V, aJ(SC) of 20.80 mA cm(-2), and an FF of 74.55% without any additive.
Intelligent Environmental Sensing: Fabrication of Switchable, Reusable, and Highly Sensitive Gas Sensors with Spiropyran-Grafted Anodic Aluminum Oxide Templates
(2020-06-04)
Lee, Lin-Ruei
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Karapala, Vamsi Krishna
;
Lin, Yu-Liang
;
He, Hung-Chieh
;
Chen, Jiun-Tai
Monitoring undesired pH deviations in the surroundings is one of the most pervasive issues of environment and industry, and developing efficient, economical, portable, and reusable membranes for pH monitoring is urgently needed. Herein, we report novel smart nanomembranes (SNMs) that are made up of anodic aluminum oxide (AAO) templates grafted with spiropyran molecules. The ultraviolet and visible light responses of the SNMs under acid vapors are investigated. Under UV irradiation, the ring-closed spiropyran on the AAO templates transform to ring-opened merocyanine, which contains phenolate oxygen and can be further protonated by acids. Such a protonation process not only shows evident color changes but also endows SNMs with pH-responsive properties, which are further investigated by UV-vis diffuse reflectance spectroscopy. Furthermore, to demonstrate the pH-responsive properties of the SNM, common volatile acids such as hydrochloric acid, nitric acid, formic acid, and acetic acid are tested. The SNM shows conspicuous sensibility, reusability, and reversibility during the processes of irradiation, protonation, and deprotonation. Therefore, the newly developed SNM can be an excellent alternative to the existing pH sensors for the detection of pH variations in environment and industry.
Laser-Assisted Nanowetting: Selective Fabrication of Polymer/Gold Nanorod Arrays Using Anodic Aluminum Oxide Templates
(1970-01-01)
He, Hung-Chieh
;
Yan, Ai-Ling
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Karapala, Vamsi Krishna
;
Wang, Shun-Fa
;
Shen, Ming-Hui
1D polymer nanomaterials have attracted significant interest in recent years because of their unique properties and promising applications in various fields. It is, however, still a challenge to fabricate polymer nanoarrays with desired sizes and controlled morphologies. Here, an unprecedented approach, the laser-assisted nanowetting (LAN) method, to selectively fabricate polymer nanoarrays is presented. Polystyrene (PS) is blended with gold nanorods (AuNRs), which are used to absorb the energy from the laser. After the blend films are brought in contact with AAO templates, the AuNRs at regions shone by the laser beams absorb the energy and heat the surrounding polymer chains, resulting in the formation of PS/AuNRs arrays in selected areas. This work paves a new research direction for developing template-based polymer nanomaterials.
Light-Induced Nanowetting: Erasable and Rewritable Polymer Nanoarrays via Solid-to-Liquid Transitions
(2020-08-12)
Lin, Kuan-Ting
;
Chen, Yu-Jia
;
Huang, Meng-Ru
;
Karapala, Vamsi Krishna
;
Ho, Jhih-Hao
Template wetting methods have been widely applied in the preparation of one-dimensional (1D) polymer nanomaterials. The pattern control using the template wetting methods, however, still remains a great challenge, mainly due to the nonselectivity of the polymers toward the environmental triggering. In this work, we present a facile light-induced nanowetting (LIN) method to fabricate patterned nanoarrays using anodic aluminum oxide (AAO) templates. Photoresponsive azobenzene-containing polymers (azopolymers) that exhibit light-induced reversible solidto-liquid transitions are used. Upon exposure to ultraviolet lights, the azopolymer chains can wet the nanopores of the AAO templates in a liquid state via capillary force. The azopolymer chains are then solidified by illuminating them with visible lights, resulting in the formation of azopolymer nanoarrays. Notably, using designed photomasks, the patterns of the nanoarrays can be ingeniously controlled with the characteristic of erasable and rewritable nanostructures.
Preparation and thermal dissipation of hollow carbon fibers from electrospun polystyrene/poly(amic acid) carboxylate salt core-shell fibers
(2020-05-05)
Li, Jia-Wei
;
Hsu, Hsun-Hao
;
Chang, Chia-Jui
;
Chiu, Yu-Jing
;
Tseng, Hsiao-Fan
Polyimides (PIs) possess great mechanical properties, outstanding thermal stability, solvent inertness, and the ability to be converted into carbon by thermal carbonization. Although studies on carbon materials derived from PIs have been conducted, PI-derived one-dimensional (1D) carbon materials with high surface areas, especially carbon tubes or hollow carbon fibers, have been rarely investigated. In this work, we provide a simple and facile method to prepare hollow carbon fibers by carbonizing hollow PI fibers. Blend solutions of poly(amic acid) carboxylate salts (PAAS) and polystyrene (PS) are electrospun to form core-shell PS/PAAS fibers, in which the PS and PAAS domains are used as sacrificial and precursor materials, respectively. By imidizing the PAAS to PI and selectively removing PS, hollow PI fibers can be obtained. Finally, the hollow PI fibers are carbonized to form hollow carbon fibers. The fiber samples at different stages are examined by thermal gravimetric analysis (TGA), Raman spectrometry, Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The infrared images show that the thermal energy transfer rates of the hollow carbon fibers are higher than those of the hollow PI and PS/PI core-shell fibers, which can be attributed to the better thermal conductivity of carbon resulting from the covalent sp(2) bonding between carbon atoms and the high surface area of the hollow structure.
Reproducible and Bendable SERS Substrates with Tailored Wettability Using Block Copolymers and Anodic Aluminum Oxide Templates
(1970-01-01)
Lin, Yu-Liang
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Karapala, Vamsi Krishna
;
Shen, Ming-Hui
;
Chen, Yi-Fan
;
He, Hung-Chieh
Surface properties are essential for substrates exhibiting high sensitivity in surface-enhanced Raman scattering (SERS) applications. In this work, novel SERS hybrid substrates using polystyrene-block-poly(methyl methacrylate) and anodic aluminum oxide templates is presented. The hybrid substrates not only possess hierarchical porous nanostructures but also exhibit superhydrophilic surface properties with the water contact angle approximate to 0 degrees. Such surfaces play an important role in providing uniform enhanced intensities over large areas (relative standard deviation approximate to 10%); moreover, these substrates are found to be highly sensitive (limit of detection approximate to 10(-12) m for rhodamine 6G (R6G)). The results show that the hybrid SERS substrates can achieve the simultaneous detection of multicomponent mixtures of different target molecules, such as R6G, crystal violet, and methylene blue. Furthermore, the bending experiments show that about 70% of the SERS intensities are maintained after bending from approximate to 30 degrees to 150 degrees.