Kyung Chul Sun

Integrating high electrical conductivity and photocatalytic activity in cotton fabric by cationizing for enriched coating of negatively charged graphene oxide.

Electroconductive textiles have attended tremendous focus recently and researchers are making efforts to increase conductivity of e-textiles, in order to increase the use of such flexible and low cost textile materials. In this study, surface conductivity and photo catalytic activity of standard cotton fabric (SCF) was enhanced by modifying its surface charge, from negative to positive, using Bovine Serum Albumin (BSA) as a cationic agent, to convert it into cationised cotton fabric (CCF). Then, both types of fabrics were dip coated with a simple dip and dry technique for the adsorption of negatively charged graphene oxide (GO) sheets onto its surface. This resulted in 67.74% higher loading amount of GO on the CCF making self-assembly. Finally, this coating was chemically converted by vapor reduction using hydrazine hydrate to reduced graphene oxide (rGO) for restoration of a high electrical conductivity at the fabric surface. Our results revealed that with such high loading of GO, the surface resistance of CCF was only 40Ω/sq as compared to 510Ω/sq of the SCF and a 66% higher photo catalytic activity was also achieved through cationization for improved GO coating. Graphene coated SCF and CCF were characterized using FE-SEM, FTIR, Raman, UV-vis, WAXD, EDX and XPS spectroscopy to ascertain successful reduction of GO to rGO. The effect of BSA treatment on adsorption of cotton fabric was studied using drop shape analyzer to measure contact angle and for thermal and mechanical resistance, the fabric was tested for TGA and tensile strength, respectively. rGO coated fabric also showed slightly improved thermal stability yet a minor loss of strength was observed. The high flexibility, photocatalytic activity and excellent conductivity of this fabric suggests that it can be used as an electrode material for various applications.

Hydrothermal synthesis of TiO2 nanotubes and their application as an over-layer for dye-sensitized solar cells

Different nanostructures of TiO2 play an important role in the kinetics of dye sensitized solar cells (DSSC) and affect the overall light harvesting efficiency of the cells. This article describes that the one dimensional nanostructure of TiO2 (nanotubes) can increase the light scattering effect, light harvesting effect and electron transport in the DSSC to improve its performance. Pure anatase TiO2 nanotubes were synthesized by a hydrothermal method using commercial material (P25) due to which the manufacturing cost of the DSSC was enormously reduced. To enhance the power conversion efficiency of the DSSC, a new type of double layered photoanode was prepared and optimized by using TiO2 nanoparticles as the main layer and TiO2 nanotubes (TNT) as the over-layer. These prepared cells were analysed by optical, photovoltaic and electrochemical measurement systems. The cells having the TNT over-layer showed longer electron life time, higher BET surface area and pore volume and 40% improved light harvesting efficiency. This new and optimized structure will be concrete fundamental background towards the development of the applications of next generation dye-sensitized solar cells.

Fabrication of textile fabric counter electrodes using activated charcoal doped multi walled carbon nanotube hybrids for dye sensitized solar cells

Textile fabric electrodes have attained increasing demand as they offer the benefits of light weight, flexibility, and low cost. In this work, we fabricated an activated charcoal doped multi walled carbon nanotube (AC doped MWCNT) hybrid and printed on polyester woven fabric. This carbon fabric composite was used as a counter electrode (CE) in dye sensitized solar cells (DSSCs), so as to replace expensive platinized FTO (fluorinated tin oxide) glass. A variety of mesoporous carbon structures were synthesized by using different types of charcoal together with MWCNTs. Morphological characterization revealed that the highly porous defect rich carbon structure consists of synchronized features of 3D carbon decorated with the MWCNT network. The excessive oxygen surface groups can reduce a large amount of polymer gel electrolyte and locate manifold catalytic sites for the reduction of tri-iodide (I3−). Electrochemical investigations confirmed that this carbon fabric composite has high electrocatalytic activity (ECA) and exhibited a very low charge transfer resistance (RCT) of 1.38 Ω. The resulting N719 DSSCs consisting of this unique carbon coated textile fabric CE filled with the polymeric electrolyte show a power conversion efficiency (PCE) of 7.29%, outperforming the platinized FTO glass CE. Such facile assembly of this novel textile fabric CE is quite promising for the mass production of next generation textile structured solar cells.

Highly efficient and durable dye-sensitized solar cells based on a wet-laid PET membrane electrolyte

Polyethylene terephthalate (PET), a commonly used textile fiber, was used in the form of a wet-laid non-woven fabric as a matrix for electrolytes in dye-sensitized solar cells (DSSCs). Also functioning as a separator between the photoanode and cathode of a DSSC, this non-woven membrane was prepared by a well-known wet-laid manufacturing process followed by calendaring to reduce the thickness and increase the uniformity of the structure. This membrane can better absorb the electrolyte turning into a quasi-solid, providing excellent interfacial contact between both electrodes of the DSSC and preventing a short circuit. An optimized membrane provides a better and more desirable structure for ionic conductivity, resulting in the improvement of the photovoltaic performance after calendaring. The quasi-solid-state DSSC assembled with an optimized membrane exhibited 10.248% power conversion efficiency (PCE) at 100 mW cm−2. With the aim of increasing the absorbance, the membrane was also plasma-treated with argon and oxygen separately, which resulted in retention of the electrolyte, avoiding its evaporation, and a 15% longer lifetime of the DSSC compared to liquid electrolytes. The morphology of the membrane was studied by field emission scanning electron microscopy, and the photovoltaic properties and impedance spectroscopy of the cells were studied using polarization curves and electrochemical impedance spectroscopy, respectively. The results suggest that this novel membrane can be used in high-efficiency solar cells, increasing their lifetime without compromising the photovoltaic properties.

Fabrication of a flexible and conductive lyocell fabric decorated with graphene nanosheets as a stable electrode material

Textile electrodes are highly desirable for wearable electronics as they offer light-weight, flexibility, cost effectiveness and ease of fabrication. Here, we propose the use of lyocell fabric as a flexible textile electrode because of its inherently super hydrophilic characteristics and increased moisture uptake. A highly concentrated colloidal solution of graphene oxide nanosheets (GONs) was coated on to lyocell fabric and was then reduced in to graphene nanosheets (GNs) using facile chemical reduction method. The proposed textile electrode has a very high surface conductivity with a very low value of surface resistance of only 40Ωsq(-1), importantly without use of any binding or adhesive material in the processing step. Atomic force spectroscopy (AFM) and Transmission electron microscopy (TEM) were conducted to study the topographical properties and sheet exfoliation of prepared GONs. The surface morphology, structural characterization and thermal stability of the fabricated textile electrode were studied by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), X ray photon spectroscopy (XPS), Raman spectroscopy, Wide angle X ray diffraction spectroscopy (WAXD) and Thermogravimetric analysis (TGA) respectively. These results suggest that the GONs is effectively adhered on to the lyocell fabric and the conversion of GONs in to GNs by chemical reduction has no adverse effect on the crystalline structure of textile substrate. The prepared graphene coated conductive lyocell fabric was found stable in water and electrolyte solution and it maintained nearly same surface electrical conductivity at various bending angles. The electrical resistance results suggest that this lyocell based textile electrode (L-GNs) is a promising candidate for flexible and wearable electronics and energy harvesting devices.

Highly Functional TNTs with Superb Photocatalytic, Optical, and Electronic Performance Achieving Record PV Efficiency of 10.1% for 1D-Based DSSCs

Different nanostructures of TiO2 play an important role in the photocatalytic and photoelectronic applications. TiO2 nanotubes (TNTs) have received increasing attention for these applications due to their unique physicochemical properties. Focusing on highly functional TNTs (HF-TNTs) for photocatalytic and photoelectronic applications, this study describes the facile hydrothermal synthesis of HF-TNTs by using commercial and cheaper materials for cost-effective manufacturing. To prove the functionality and applicability, these TNTs are used as scattering structure in dye-sensitized solar cells (DSSCs). Photocatalytic, optical, Brunauer-Emmett-Teller (BET), electrochemical impedance spectrum, incident-photon-to-current efficiency, and intensity-modulated photocurrent spectroscopy/intensity-modulated photovoltage spectroscopy characterizations are proving the functionality of HF-TNTs for DSSCs. HF-TNTs show 50% higher photocatalytic degradation rate and also 68% higher dye loading ability than conventional TNTs (C-TNTs). The DSSCs having HF-TNT and its composite-based multifunctional overlayer show effective light absorption, outstanding light scattering, lower interfacial resistance, longer electron lifetime, rapid electron transfer, and improved diffusion length, and consequently, J SC , quantum efficiency, and record photoconversion efficiency of 10.1% using commercial N-719 dye is achieved, for 1D-based DSSCs. These new and highly functional TNTs will be a concrete fundamental background toward the development of more functional applications in fuel cells, dye-sensitized solar cells, Li-ion batteries, photocatalysis process, ion-exchange/adsorption process, and photoelectrochemical devices.

A PVdF-based electrolyte membrane for a carbon counter electrode in dye-sensitized solar cells

This research demonstrates the design and operation of a dye-sensitized solar cell (DSSC) with a multi-walled carbon nanotube counter electrode (CE) and a pore-filled membrane consisting of polyvinylidene fluoride-co-hexafluoropropylene (PVdF-co-HFP) as an electrolyte. In this cell, the internal resistance was substantially reduced and the efficiency was found to be as high as 6.04% under 1 sun. For this purpose, a sequence of experiments was carried out to demonstrate that the PVdF-co-HFP membrane possessed superior porosity to absorbed electrolytes and is more compatible with MWCNT CE as compared to the commonly used liquid electrolyte. For a comparison of results, different types of DSSC assemblies composed of MWCNT CEs were fabricated with liquid-, gel- and electrolyte-filled PVdF-co-HFP membranes. Morphological studies showed that the PVdF-co-HFP membrane is a regular and highly porous nano-web which provides optimized interfacial contact with defect-rich MWCNT CE. Detachment of the carbon particles from the CE causes short circuits and lower efficiency of the DSSCs. The proposed DSSC design not only lowers the interfacial charge transfer resistance (RCT = 2.98 Ω) but also reduces the risk of short circuits in the cell. This sustainable and highly efficient DSSC structure provides a new method for the simple fabrication of flexible solar cells and electronic devices.

An evidence for an organic N-doped multiwall carbon nanotube heterostructure and its superior electrocatalytic properties for promising dye-sensitized solar cells

A novel organic heteroatom doping technique is proposed for the synthesis of N-doped multiwall carbon nanotube (MWCNT) heterostructures. The approach involves the effective doping of MWCNTs with nitrogen via a cationised bovine serum albumin (cBSA) protein complex. The cationization of BSA releases an exceptional number of activated nitrogen species present in localized amino groups, which are further embedded into the MWCNT framework. The amino groups present in BSA act as nitrogen donors and surface stabilizing agents to generate a highly conductive and functionalized carbon heterostructure. The doped nitrogen was present in the form of pyridinic and pyrrolic states, as evidenced by XPS analysis. Organic N-doped MWCNTs with predominant pyridinic N atoms displayed superior charge transfer (RCT = 0.06 Ω) owing to their superior electrocatalytic activity. A DSSC fabricated with organic N-doped MWCNT heterostructures exhibited a high conversion efficiency of 9.55%, which was similar to that of a Pt cathode, with an efficiency of 9.89%. The superior electrochemical performance of organic N-doped MWCNT heterostructures is due to the high charge polarization arising from the difference in electronegativity between nitrogen and carbon as well as the structural strain caused by the cationic BSA protein complex. Our proposed system provides new routes for the synthesis of organic heteroatom-doped nanomaterials for promising energy storage devices.