Evaluation of Pt-based alloy/graphene nanohybrid electrocatalysts for triiodide reduction in photovoltaics

Dao, Van-Duong,Larina, Liudmila L.,Tran, Quoc Chinh,Bui, Van-Tien,Nguyen, Van-Toan,Pham, Thanh-Dong,Mohamed, Ibrahim M.A.,Barakat, Nasser A.M.,Huy, Bui The,Choi, Ho-Suk Elsevier 2017 Carbon Vol.116 No.-

<P>This work focuses on systematic studies of dissolution engineering for Pt0.9M0.1/graphene(M = Au, Co, Cu, Fe, Mo, Ni, Pd, Ru, and Sn) counter electrodes (CEs). The developed nanohybrid materials exhibit higher catalytic activity and electrical conductivity compared with those of Pt/graphene CEs. The results also indicate the improved stability of the developed CEs in iodide electrolyte. Furthermore, the trend in the variation of the reactivity of the PtM alloys agrees well with the concept of density functional theory (one-electron description). An enhancement in the catalytic activity of the developed nanohybrids results from the electronic effect that originates from an upward shift of the platinum d-band to the Fermi energy level upon alloying. Thus, the Pt(0.9)M(0.1)graphene nanohybrids are cost-effective alternative CE materials to the expensive Pt. The obtained results provide a foundation for enhancing the catalytic activities of CEs for dye-sensitized solar cells (DSCs). The implementation of the Pt0.9M0.1/graphene nanohybrids offers significant potential for increasing the efficiency of DSCs. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Graphene-based RuO₂ nanohybrid as a highly efficient catalyst for triiodide reduction in dye-sensitized solar cells

Dao, Van-Duong,Larina, Liudmila L.,Lee, Joong-Kee,Jung, Kwang-Deog,Huy, Bui The,Choi, Ho-Suk Elsevier 2015 Carbon Vol.81 No.-

<P><B>Abstract</B></P> <P>This study is the first to report the synthesis of graphene-based RuO<SUB>2</SUB> nanohybrid materials and their application as a counter electrode (CE) in dye-sensitized solar cells (DSCs). Ru nanoparticles (RuNPs) with an average size of 9nm were uniformly immobilized on the surface of reduced graphene oxide (RGO) with the simultaneous co-reduction of Ru precursor ions and graphene oxide (GO) to Ru atoms and RGO, respectively, through dry plasma reduction (DPR) under atmospheric pressure and at near room temperature without using any toxic chemicals. Since RuNPs are more susceptible to oxidation, Ru atoms located on the surface of RuNPs are further oxidized to RuO<SUB>2</SUB> in atmosphere. The resulting RuO<SUB>2</SUB>-RGO nanohybrid with a very small amount of Ru exhibits low charge transfer resistance, low diffusion impedance and good long-term stability. The application of RuO<SUB>2</SUB>-RGO nanohybrid as an alternative CE for DSCs leads to high energy conversion efficiency of 8.32±0.15%, which is comparable to the value of 8.16±0.13% of DSCs based on a Pt-NP CE prepared by DPR. This study also discusses the influence of hydrogen species existing in either precursor ions or graphenes on the formation of uniform and well-dispersed NPs on the substrates.</P>

Plasma Reduction of Nanostructured TiO₂ Electrode to Improve Photovoltaic Efficiency of Dye-Sensitized Solar Cells

Dao, Van-Duong,Larina, Liudmila L.,Choi, Ho-Suk The Electrochemical Society 2014 Journal of the Electrochemical Society Vol.161 No.14

<P>This study first reports the surface modification of nanostructured TiO<SUB>2</SUB> film on an FTO glass substrate using plasma reduction; we also report the application of this film to a working electrode for enhancement of the efficiency of dye-sensitized solar cells. The change in the electronic structure of the TiO<SUB>2</SUB> films was confirmed by XPS measurements. IMPS and IMVS studies showed that the plasma reduction induced increases of the electron diffusion coefficient and the electron recombination lifetime. The longer electron diffusion length prevents the charge recombination with oxidized redox, which is controlled by trap-limited electron diffusion in the TiO<SUB>2</SUB>. These results can be explained by the increase of number of the Ti<SUP>3+</SUP> valence states (electron traps) and their occupancy, induced by plasma reduction. The obtained data are consistent with the remarkable increase in the values of FF and J<SUB>sc</SUB>. Plasma reduction facilitated charge transport in sensitized TiO<SUB>2</SUB> due to the increase in the charge collection efficiency. The higher <I>V<SUB>oc</SUB></I> value was ascribed to the upward moving of the quasi-Fermi level due to the increase in the density of the Ti<SUP>3+</SUP> valence states and their occupancy. Thus, we achieved an enhancement in efficiency of 11.6% for 6 hours of dye adsorption.</P>

A facile synthesis of bimetallic AuPt nanoparticles as a new transparent counter electrode for quantum-dot-sensitized solar cells

Dao, Van-Duong,Choi, Youngwoo,Yong, Kijung,Larina, Liudmila L.,Shevaleevskiy, Oleg,Choi, Ho-Suk Elsevier 2015 Journal of Power Sources Vol.274 No.-

<P><B>Abstract</B></P> <P>This study first reports the synthesis of AuPt bimetallic nanoparticles (AuPt-BNPs) on an FTO glass substrate using dry plasma reduction (DPR) and its application as an alternative transparent counter electrode (CE) for quantum-dot-sensitized solar cells (QDSCs) operated under bi-side illumination. DPR is an economically feasible and ecologically sustainable method. The formation of ultrafine crystalline AuPt-BNPs on an FTO substrate is confirmed through TEM, HRTEM with HAADF-STEM and HAADF-STEM-EDS analyses. The mechanism for controlling the size, mono-dispersity, and areal number density of nanoparticles on the substrate surface is suggested. The CE fabricated with AuPt-BNPs exhibits a high electro-catalytic activity without losing the optical transmittance of the FTO substrate. The QDSC employing the AuPt-BNP electrode reaches efficiencies of 2.4% under front-side illumination and 2.2% under back-side illumination. Bi-side illumination yields an efficiency of 3.4%, which is comparable to an efficiency of 3.7% obtained for the QDSC with the state-of-the-art CE.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An ultrafine crystalline AuPt-BNP electrode was successfully fabricated using DPR. </LI> <LI> The formation mechanism of BNPs provides a way for tuning catalyst morphology. </LI> <LI> The BNPs show high catalytic activity without reducing the optical transmittance. </LI> <LI> Bi-side illumination yields 3.4% efficiency comparable to 3.7% of Au-sputtered CE. </LI> <LI> The proposed method can be a key technique for efficient and transparent QDSCs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Dry plasma synthesis of a MWNT–Pt nanohybrid as an efficient and low-cost counter electrode material for dye-sensitized solar cells

Dao, Van-Duong,Choi, Ho-Suk The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.79

<P>Dry plasma reduction (DPR) is an excellent approach for easily and uniformly immobilizing many platinum nanoparticles (Pt-NPs) with a size of 2–3 nm on both inner and outer surfaces of MWNTs under atmospheric pressure and at near room temperature. The MWNT–Pt nanohybrid exhibits quite low charge transfer resistance for dye-sensitized solar cells.</P> <P>Graphic Abstract</P><P>Dry plasma reduction (DPR) is an excellent approach for easily and uniformly immobilizing many platinum nanoparticles (Pt-NPs) with a size of 2–3 nm on both inner and outer surfaces of MWNTs under atmospheric pressure and at near room temperature. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc42151a'> </P>

Pt-coated cylindrical micropatterned honeycomb Petri dishes as an efficient TCO-free counter electrode in liquid junction photovoltaic devices

Dao, Van-Duong,Bui, Van-Tien,Choi, Ho-Suk Elsevier Sequoia 2018 Journal of Power Sources Vol. No.

<P><B>Abstract</B></P> <P>The Pt layer deposited on a cylindrical micro cavity patterned Petri dish, which is produced using a one-step solvent-immersion phase separation, is fabricated for the first time as an FTO-free counter electrode (CE) for dye-sensitized solar cells (DSCs). Due to the high specific active surface area of the Pt-deposited honeycomb substrate CE, the efficiency of the DSC using the developed CE substrate is enhanced by 14.5% compared with the device using a Pt-sputtered flat substrate. This design strategy has potential in fabricating highly efficient and low-cost CE materials with FTO-free substrates for DSCs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A very simple, low cost, scalable, and single-step method for FTO-free CE is developed. </LI> <LI> It is a Pt layer deposited on the cylindrical micro-patterned honeycomb Petri dish. </LI> <LI> An efficiency enhancement of 14.5% is achieved compared with Pt-sputtered flat CE. </LI> <LI> The CE also shows an improved stability in iodide electrolyte. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Balance between the charge transfer resistance and diffusion impedance in a CNT/Pt counter electrode for highly efficient liquid-junction photovoltaic devices

Dao, Van-Duong,Choi, Ho-Suk Elsevier 2018 Organic electronics Vol.58 No.-

<P><B>Abstract</B></P> <P>This study investigates changes in the charge transfer resistance (R<SUB>ct</SUB>) and diffusion impedance (Z<SUB>w</SUB>) according to the thickness of a CNT/Pt layer coated onto an FTO glass counter electrode (CE) to improve the photovoltaic performance of dye-sensitized solar cells (DSCs). For this purpose, we carefully controlled the thickness of the CE by using different amounts of CNT/Pt in the paste. Note that both R<SUB>ct</SUB> and Z<SUB>w</SUB> decrease with an increase in the thickness of the CEs. Power conversion efficiencies of 7.77, 8.21, 7.58 and 7.36% are determined for DSCs with thicknesses of the CNT/Pt layer of 1, 3.2, 10 and 18 μm, respectively. The obtained results are in good agreement with the changes in the ratio of R<SUB>ct</SUB>/Z<SUB>w</SUB>. When the ratio of R<SUB>ct</SUB>/Z<SUB>w</SUB> becomes one and the R<SUB>ct</SUB> value is less than 1 Ωcm<SUP>2</SUP>, the device shows the best performance. Because this strategy is simple and effective, it can be useful for developing cost-effective CE materials for DSCs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The ratio of R<SUB>ct</SUB>/Z<SUB>w</SUB> is optimized for high photovoltaic performance of DSCs. </LI> <LI> The effect of CNT/Pt layer thickness on the photovoltaic performance of DSCs is investigated. </LI> <LI> The best performance is obtained when the ratio of R<SUB>ct</SUB>/Z<SUB>w</SUB> becomes 1 and the R<SUB>ct</SUB> value is less than 1 Ωcm<SUP>2</SUP>. </LI> <LI> This approach can be useful for developing cost-effective CE materials for DSCs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Suppression of Charge Recombination in Dye-Sensitized Solar Cells Using the Plasma Treatment of Fluorine-Doped Tin Oxide Substrates

Dao, Van-Duong,Larina, Liudmila L.,Choi, Ho-Suk The Electrochemical Society 2015 Journal of the Electrochemical Society Vol.162 No.12

<P>This study presents a novel strategy for increasing the efficiency of dye-sensitized solar cells (DSCs) through modifying the surface of the fluorine-doped tin oxide (FTO) substrates using an atmospheric pressure plasma treatment. This strategy allows the suppression of charge recombination at the interface between the FTO substrate and electrolyte due to the formation of a thin, compact TiO<SUB>2</SUB> blocking layer (BL) on the FTO surface without cracks and holes. Furthermore, the transmittance of the plasma-treated FTO/BL interface is higher than that of the pristine structure due to the compact morphology of the BL on the plasma-treated FTO. Thus, this strategy enables simultaneous improvement in light harvesting and photo-generated carrier collection. DSCs that use plasma-treated FTO substrates achieve higher efficiencies of 8.86% compared with the 8.04% of the reference device.</P>

Comparison between Water and N-Tetradecane as Insulation Materials through Modeling and Simulation of Heat Transfer in Packaging Box for Vaccine Shipping

Van-Duong Dao,Ik-Kyu Jin,Ho Hur,Ho-Suk Choi 한국청정기술학회 2016 청정기술 Vol.22 No.1

Pt Nanourchins as Efficient and Robust Counter Electrode Materials for Dye-Sensitized Solar Cells

Dao, Van-Duong,Choi, Ho-Suk American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.1

<P>This study reports on the synthesis of Pt nanourchins (PtNUs) on FTO glass surfaces and their application as an efficient and robust counter electrode (CE) in dye-sensitized solar cells (DSCs). PtNUs with sizes in the range of 100-300 nm are successfully synthesized on FTO surfaces via a simple room temperature chemical reduction of H2PtCl6 using formic acid. Note that the PtNUs have numerous Pt nanowires with 2 nm diameters and 12 nm lengths. The PtNU CE exhibits very low charge-transfer resistance for DSCs. The efficiency of DSCs fabricated with PtNU CEs is 9.39%, which is higher than that of devices assembled with Pt-sputtered CEs (8.51%).</P>