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Now showing items 1 - 16 of 95

  • High-performance printable electrolytes for dye-sensitized solar cells

    Liu, I-Ping   Hung, Wei-Ning   Teng, Hsisheng   Venkatesan, Shanmugam   Lin, Jian-Ci   Lee, Yuh-Lang  

    High-performance quasi-solid-state electrolytes with printable characteristics are developed herein for dye-sensitized solar cells (DSSCs). The printable electrolytes are prepared based on a 3-methoxypropionitrile liquid electrolyte containing I-/I-3(-) redox couples. Poly(ethylene oxide) (PEO) and poly(vinylidene fluoride) (PVDF) are utilized as agents to regulate the viscosity and properties of the electrolyte pastes; furthermore, TiO2 nanoparticles are used as a filler to enhance the performance of the electrolytes. The results show that PEO is a required material to prepare the electrolyte pastes for operation by a printing process. However, if only PEO is utilized, the conversion efficiency of the corresponding cell (7.65%) is much lower than that of the liquid one (8.34%). By introducing PVDF as a co-regulating agent, the resultant cell can achieve an efficiency of 8.32% similar to that of the liquid cell, mainly attributed to the decrease of charge transfer resistance at the electrolyte/Pt counter electrode interface. In addition, if 4 wt% TiO2 nanoparticles are introduced as fillers into the printable electrolyte, the cell efficiency can be further increased to 8.91%. By applying this printable electrolyte to a sub-module cell, a conversion efficiency of 6.45% is achieved. The DSSCs prepared by the printing process are stable under a long-term stability test at 60 degrees C.
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  • Diode-like gel polymer electrolytes for full-cell lithium ion batteries

    Lin, Yong-Yi   Chen, Yen-Ming   Hou, Sheng-Shu   Jan, Jeng-Shiung   Lee, Yuh-Lang   Teng, Hsisheng  

    This study designs a positive-intrinsic-negative (PIN)-diode-like gel polymer electrolyte (GPE) for a full-cell graphite vertical bar electrolyte vertical bar LiFePO4 lithium ion battery to facilitate interfacial ion transfer at both the anode and cathode. The diode-like GPE comprises an intrinsic poly(acrylonitrile-co-methylacrylate)-hosted electrolyte layer, as well as positive and negative layers that are synthesized by doping the intrinsic layer with TiO2 and SiO2 nanoparticles, which respectively exhibits positive and negative zeta potentials. The positive layer that adsorbs PF6- anions is in contact with the LiFePO4 cathode of the battery to facilitate the transfer of Li+ cations across the interface. The negative layer, which is in contact with the graphite anode, adsorbs Li+ cations to suppress accumulation and prevent the intercalation of solvated Li+ into the graphitic framework. The intrinsic layer acts as a neutralization zone to lower the current-rectification effect of the p-n junction. This PIN-configuration design for electrolytes enhances the ultimate capacity of the full-cell battery, exhibits high rate capacity retention, and increases the life-span (87% capacity retained after 500 charge-discharge cycles).
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  • Adsorption Behavior of TBPS in the Process of Cu Electrodeposition on an Au Film

    Chen, Liang-Huei   Liu, Yung-Fang   Krug, Klaus   Lee, Yuh-Lang  

    The adsorption behavior of an Cu electroplating additive, 3,3 thiobis-(1-propanesulfonic acid sodium salt) (TBPS) in a process of Cu deposition onto a single crystalline Au(111) surface is studied by an in-situ Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS). The SEIRAS spectra of the TBPS adlayer on a Cu film is investigated first and compared to that on an Au film. These results are utilized to evaluate the characteristics of TBPS adlayer on the electrode surface during the Cu deposition and stripping processes. The results show that the SEIRAS spectra of TBPS adsorbed on the Cu film resembles closely to that on the Au film, and the most pronounced peaks are symmetric S-O (ss-SO) and asymmetric S-O (as-SO) stretching modes. However, the as-SO band is sharper with a higher intensity on the Cu film. Since the ss-SO and as-SO peaks correspond to the molecular with upright and lie-down orientations, respectively, it implies that the TBPS molecules have higher ratio of lie-down orientation on the Cu film. In the Cu electrodeposition process, the cyclic voltammetry (CV) result shows that the presence of the TBPS in the HClO4 solution can decrease the inhibition effect of HClO4 to the Cu deposition. For the spectra measured at various potential during cathodic and anodic sweeping, an obvious change of the spectra occurs at ca. 0.6 V, the initiation of Cu underpotential deposition (Cu-UPD). For potentials higher and lower than 0.6 V, the spectra are similar, respectively, to those measured for the Au and Cu films. This result indicates that the TBPS molecules originally adsorbing on the Au film transfer to the surface of deposited Cu layer. This inference is also confirmed by the variation in wavenumber and peak intensity of ss-SO and as-SO peaks during the potential sweeping.
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  • High performance carbon black counter electrodes for dye-sensitized solar cells

    Wu, Chia-Shing   Chang, Ting-Wei   Teng, Hsisheng   Lee, Yuh-Lang  

    Carbon black (CB) thin films are prepared using a doctor blade process and utilized as counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). Poly(vinylidene fluoride) (PVDF) is used as a binder to regulate the viscosity of the CB paste to facilitate the doctor blade process. The PVDF is then removed via thermal treatment at 350 or 450 degrees C. The effects of CB composition (8-15 wt%) and the heat-treatment temperature on the electrochemical properties of the CB electrodes are studied, as well as on the performance of the corresponding DSSCs. The results show that, after the heat treatment, all CB films demonstrate a mesoporous structure. Film thickness increases with increased CB concentration. CB films heat-treated at 350 degrees C exhibit low electrochemical activity, high charge transfer resistance, and poor performance when utilized in DSSCs. These results are attributed to the presence of residual PVDF. By elevating the treating temperature to 450 degrees C, PVDF is completely removed and the electrochemical properties of the resultant CB films resemble closely those of platinum (Pt) film. The DSSCs using these CB CEs achieve conversion efficiencies (8.27-8.35%) comparable to cells using Pt (8.29%). (C) 2016 Elsevier Ltd. All rights reserved.
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  • Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting

    Chen, Chia-Yuan   Jian, Zih-Hong   Huang, Shih-Han   Lee, Kun-Mu   Kao, Ming-Hsuan   Shen, Chang-Hong   Shieh, Jia-Min   Wang, Chin -Li   Chang, Chiung-Wen   Lin, Bo-Zhi   Lin, Ching-Yao   Chang, Ting-Kuang   Chi, Yun   Chi, Cheng-Yu   Wang, Wei-Ting   Tai, Yian   Lu, Ming-De   Tung, Yung-Liang   Chou, Po-Ting   Wu, Wen-Ti   Chow, Tahsin J.   Chen, Peter   Luo, Xiang-Hao   Lee, Yuh-Lang   Wu, Chih-Chung   Chen, Chih-Ming   Yeh, Chen-Yu   Fan, Miao-Syuan   Peng, Jia-De   Ho, Kuo-Chuan   Liu, Yu-Nan   Lee, Hsiao-Yi   Chen, Chien-Yu   Lin, Hao-Wu   Yen, Chia-Te   Huang, Yu-Ching   Tsao, Cheng-Si   Ting, Yu-Chien   Wei, Tzu-Chien   Wu, Chun-Guey  

    Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current voltage (I-V) characteristics as an indicator to qualify the I-V sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications.
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  • In Situ STM Study of Cu Electrodeposition on TBPS-Modified Au(111) Electrodes

    Liu, Yung-Fang   Krug, Klaus   Lin, Pin-Chun   Chiu, Yong-Da   Dow, Wei-Ping   Yau, Shueh-Lin   Lee, Yuh-Lang  

    The impact of 3,3'-thiobis(1-propanesulfonic acid, sodium salt) (TBPS) on Cu/Au(111) electrodeposition has been investigated by electrochemical methods and scanning tunneling microscopy (STM). Cyclic voltammetry and galvanostatic experiments indicate that Cu growth on Au(111) - which is known to be strongly kinetically hindered in additive-free, aqueous perchloric acid solutions - proceeds significantly faster in the presence of TBPS. The TBPS molecules either "float" on top of the growing film or become incorporated into the deposit. Complementary in situ STM studies show that Cu underpotential deposition (UPD) proceeds via two distinct mechanisms. One-dimensional growth of Cu stripes was observed between 0.05 and 0.35 V-RHE for TBPS-modified Au(111) electrodes. Each stripe is composed of two or three parallel rows of Cu atoms oriented along the main crystallographic directions of the Au(111) substrate. An increase of the TBPS concentration near the solid/liquid interface restricts the Cu stripe growth to a narrow potential regime between 0.3 and 0.35 V-RHE and two-dimensional Cu island growth becomes the favored growth mechanism. The latter fully dominates in TBPS-containing electrolyte. Cu growth in the overpotential deposition (OPD) regime results in a smooth Cu film with low surface roughness, in contrast to defect-mediated 3D island growth in additive-free electrolytes. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.057202jes] All rights reserved.
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  • Thermal and angular dependence of next-generation photovoltaics under indoor lighting

    Chen, Chia-Yuan   Kuo, Ting-Yang   Huang, Chien-Wu   Jian, Zih-Hong   Hsiao, Po-Tsung   Wang, Chin-Li   Lin, Jian-Ci   Chen, Chien-Yu   Chen, Chao-Hsuan   Tung, Yung-Liang   Tsai, Ming-Chi   Huang, Kuan-Min   Chen, Chih-Ming   Hsu, Cheng-Wei   Chen, Yen-Chiao   Pei, Zingway   Tingare, Yogesh S.   Chou, Hsien-Hsin   Yeh, Chen-Yu   Lin, Ching-Yao   Lee, Yuh-Lang   Lin, Hao-Wu   Meng, Hsin-Fei   Chou, Pi-Tai   Wu, Chun-Guey  

    Next-generation photovoltaic technologies such as dye-sensitized solar cells, organic thin-film photovoltaics and perovskite solar cells are promising to efficiently harvest ambient light energy. However, more and deeper understanding of their photovoltaic characteristics is essential to create new applications under room light illumination. In this study, for the first time, the difference in temperature coefficients and angular dependence of photovoltaic parameters for the large-area devices are investigated systematically under the compact fluorescent lamp and light-emitting diode light. These emerging photovoltaic devices, compared with the single crystalline silicon solar cells, not only have higher open-circuit voltage (up to approximate 1 V) and better power conversion efficiency (in the range of 9.2% similar to 22.6%) but also exhibit less temperature dependent voltage and output power (< -0.6% degrees C-1), as well as broader angular response (over 75 degrees). The state-of-the-art dye-sensitized and organic thin-film devices also show advantageously positive temperature coefficients of current, and the latter even has positive thermal dependence of fill factor. These features suggest the next-generation photovoltaic devices are more favorable than the conventional crystalline silicon solar cells for real-life indoor applications.
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  • Photocatalytic Reforming of Sugar and Glucose into H2 over Functionalized Graphene Dots

    Nguyen, Van-Can   Ke, Nei-Jin   Le, Duy Nam   Nguyen, Ba-Son   Xiao, Yuan-Kai   Lee, Yuh-Lang   Teng, Hsisheng  

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  • Photoactive p-type PbS as a counter electrode for quantum dot-sensitized solar cells

    Lin, Cheng-Yu   Teng, Chiao-Yi   Li, Tzung-Luen   Lee, Yuh-Lang   Teng, Hsisheng  

    A photoactive PbS film synthesized by successive cycles of coating with ionic solutions and reaction can function as a performance-promoting counter electrode for quantum dot-sensitized solar cells (QDSSCs). The PbS film has a wide absorption spectrum that extends to the near infra-red region, making it capable of absorbing the long-wavelength light that penetrates the photoanode of a QDSSC. Under simulated one-sun illumination, this PbS film exhibits a p-type photovoltaic response in a polysulfide electrolyte, showing a quasi-Fermi level shift of +0.25 V. For QDSSCs consisting of a TiO2/CuInS2/CdS/ZnS photoanode and a polysulfide electrolyte, the PbS film outperforms Pt and CuS films as a counter electrode even though CuS has a much higher electrocatalytic activity in the polysulfide electrolyte than PbS. The photoactive characteristics of the PbS electrode increase the photocurrent of the resulting QDSSC. The p-type conductivity of the PbS forms a partial tandem junction between the PbS and the anode, increasing the photovoltage and the fill factor. Under one-sun illumination, a QDSSC assembled with the photoactive p-type PbS counter electrode achieves a maximum power conversion efficiency of 4.7%, which is more than 15% greater than that of a cell assembled with the highly electrocatalytically active CuS.
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  • Efficient polysulfide electrolyte for CdS quantum dot-sensitized solar cells

    Lee, Yuh-Lang   Chang, Chi-Hsiu  

    A polysulfide electrolyte considering simultaneously the penetration of the electrolyte in a mesoscopic TiO2 film and the ion dissociation in the solution is developed for application in a CdS-sensitized solar cell (CdS-DSSC). A methanol/water (7:3 by volume) solution was found to be a good solvent for fitting the requirement mentioned above. The optimal composition of the electrolyte, based on the performance of the CdS-DSSCs, was found to contain 0.5 M Na2S, 2 M S, and 0.2 M KCl. By using a photoelectrode prepared after 4 cycles of chemical bath deposition, FTO/TiO2/CdS-4, the efficiency of the CdS-DSSC obtained for this polysulfide electrolyte is 1.15% under the illumination of 100% sun (AM1.5, 100 mW cm(-2)). This efficiency is less than that obtained using I-/I-3(-) redox couple (1.84%), mainly caused from the smaller values of fill factor and open circuit potential. However, the US sensitizer is stable and, furthermore, a much higher short circuit current and IPCE (80%) are obtained by using the polysulfide electrolyte. (C) 2008 Elsevier B.V. All rights reserved.
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  • Photocatalytic reforming of sugar and glucose into H-2 over functionalized graphene dots

    Van-Can Nguyen   Ke, Nei-Jin   Nam, Le Duy   Ba-Son Nguyen   Xiao, Yuan-Kai   Lee, Yuh-Lang   Teng, Hsisheng  

    Photocatalytic reforming of biomass into H-2 combined with its counterpart, photosynthesis, constitutes a sustainable carbon cycle that produces a clean solar fuel. This study reports the use of environmentally benign graphene-based photocatalysts to effectively reform sugar and glucose. We produce a catalyst consisting of sulfur and nitrogen codoped graphene oxide dots (SNGODs) by sequentially annealing graphite-derived graphene oxide with sulfur and ammonia, exfoliating the annealed product into dots, and autoclaving the dots in an ammonia solution. The codoping introduces quaternary nitrogen into the graphene basal plane to patch the vacancy defects and autoclaving creates a conjugation between nitrogen nonbonding states and the graphitic- orbital by introducing peripheral amide and amino groups. These functionalization steps enlarge the electron resonance domain, narrowing the bandgap and inducing charge delocalization and separation. Here, SNGODs deposited with a Pt cocatalyst effectively catalyzed H-2 production from aqueous solutions of sugar and glucose under visible light irradiation for more than 80 h. The apparent quantum yields of reforming of sugar and glucose reach 11% and 7.4%, respectively, under 420 nm monochromatic irradiation. This pioneer study demonstrates the superiority of using carbon-based photocatalysts for biomass reforming and provides a structure-tuning strategy for enhancing the catalytic activity.
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  • Charge Transfer in the Heterointerfaces of CdS/CdSe Cosensitized TiO2 Photoelectrode

    Lin, Kung-Hsuan   Chuang, Cho-Ying   Lee, Yu-Yang   Li, Fung-Chieh   Chang, Yu-Ming   Liu, I-Ping   Chou, Shih-Chuan   Lee, Yuh-Lang  

    One of the key issues affecting the performance of solar cells is the behavior of carrier transfer. In this work, the time-resolved photoluminescence (TRPL) technique was utilized to investigate the electron transfer at the CdS/CdSe, TiO2/CdS, and TiO2/CdSe heterointerfaces. By varying the excitation wavelengths, photoluminescence lifetimes of CdSe and CdS in TiO2/CdSe, TiO2/CdS, TiO2/CdS/CdSe, and TiO2/CdSe/CdS photoelectrodes were measured. The results show that, for the single sensitizer electrodes (TiO2/CdS, TiO2/CdSe), the average PL lifetime of CdS (0.69 ns) is shorter than CdSe (0.99 ns), suggesting that CdS has higher electron transfer rate toward TiO2 compared with CdSe. For the TiO2/CdSe/CdS electrode, the PL lifetime of CdSe exhibits an excitation-wavelength-dependent behavior. A shorter excitation wavelength leads to a longer PL lifetime of CdSe. This additional long lifetime is ascribed to the rapid carrier transfer from the photoexcited carriers in CdS layer into the CdSe layer. On the contrary, the PL lifetime Of CdSe is independent of the excitation wavelength in the TiO2/CdS/CdSe electrode, indicating that the excited electrons in the CdS layer did not inject into the CdSe layer. This observation confirms that the charge transfer from the cosensitizers toward the TiO2 is much more efficient in the TiO2/CdS/CdSe electrode rather than in the TiO2/CdSe/CdS electrode.
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  • Mixed Polyelectrolyte?Surfactant Langmuir Monolayers at the Air/Water Interface

    Lee, Yuh-Lang   Dudek, Anna   Ke, Tai-Nian   Hsiao, Fang-Wei   Chang, Chien-Hsiang  

    Polystyrenesulfonate acid (PSS) and alkyltrimethylammonium bromide (C(n)TAB, n = 8, 14, or 18) were dissolved in a chloroform/methanol solution and cospread on an air/water interface. The surfactant-polyelectrolyte interaction leads to the formation of hydrophobic complexes which are able to spread well at the air/water interface. The effects of surfactant chain length and surfactant/polymer ratio on the characteristics of the mixed monolayers were studied in terms of surface pressure-area (pi-A) isotherm, area relaxation, and hysteresis behavior as well as the surface morphology and composition of the corresponding Langmuir-Blodgett films. The mixed monolayers prepared by cospreading method are also compared with the complex monolayers prepared by preprecipitation of the surfactant-polyelectrolyte complexes from an aqueous solution. The experimental results show that the chain length of an incorporated surfactant is the main factor determining the properties of a complex monolayer. By using a longer chain surfactant to complex with polyelectrolyte, a more condensed monolayer with higher collapse pressure and stability can be obtained. For the effect of surfactant/polymer ratio (S/P), it is found that an increase of S/P ratio not only produces more complexes capable of staying at the air/water interface but also affects the incorporation of uncomplexed surfactant into the mixed monolayer. The X-ray photoelectron spectroscopy (XPS) analysis shows that the amount of uncomplexed surfactant is higher at low SIP value (0.2) and is insignificant when the S/P value increases to about 1.0 or 2.0, where a maximum amount of complexes were formed at the interface. A further increase of S/P ratio may cause additional incorporation of uncomplexed surfactant and/or micellization of surfactant around PSS cores, depending on the surfactant chain length. A model illustrating the incorporation and spreading of the surfactant-polyelectrolyte complexes at the air/water interface was proposed.
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  • Self-organization of two-dimensional poly(3-hexylthiophene) crystals on Au(111) surfaces

    Liu, Yung-Fang   Krug, Klaus   Lee, Yuh-Lang  

    A novel approach to construct organized structures and tunable electronic properties of poly(3-hexylthiophene) (P3HT) monolayers on Au(111) surfaces was developed based on a self-assembly process in a liquid phase. On a bare Au(111) surface, P3HT adsorbs as a monolayer with a randomly oriented and curvy-wire morphology. When the gold surface was pre-modified by an iodine adlayer (I-Au(111)), the passivation effect of iodine decreases the substrate-adsorbate interaction. As a result, P3HT adsorbs as linear chains, stacking and folding into regular arrays of a polymer bundle. By controlling the electrode at more negative potentials, it is able to desorb the iodine adlayer from the substrate. The remaining P3HT adsorbs onto the Au(111) surface directly, retaining a linear and regular arrangement. However, a different electronic structure is imaged by scanning tunneling microscopy (STM). The scanning tunneling spectroscopy (STS) analysis reveals that this molecular image is associated with a 0.16 eV shift of the Fermi level toward HOMO position, indicating a stronger p-doping characteristic of the adlayer. The phenomenon is ascribed to an iodine-induced p-doping reaction which occurs during the desorption of iodine. This work demonstrates that electrode potential and pre-adsorbed halide adlayers can be effectively used to regulate the arrangement and electronic properties of adsorbed molecules on metallic substrates.
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  • Behavior of mixed multi-walled carbon nanotube/P3HT monolayer at the air/water interface

    Lo, Chia-Ling   Lee, Yuh-Lang   Hsu, Wen-Ping  

    The sidewall structure of multi-walled carbon nanotubes (MWNTs) was successfully functionalized with poly(3-hexylthiophene) (P3HT) by a non-covalent bond method. P3HT plays an important role in dispersing MWNTs, and assists them to have a stable existence at the air/water interface. The behavior of mixed MWNT/P3HT monolayer at the air/water interface was investigated after obtaining a homogeneously dispersed solution. The effect of MWNT concentration on the mixed MWNT/P3HT monolayer was investigated using the pressure-area (pi-A) isotherm, relaxation curve and transmission electron microscopy (TEM). The mixed MWNT/P3HT monolayer was transferred onto a solid substrate using the Langmuir-Blodgett (LB) technique with horizontal or vertical deposition. The multilayer film was delicately fabricated by repeated deposition of the ultra-thin film. Scanning electron microscopy (SEM) images revealed non-uniformity in morphology of the ultra-thin MWNT/P3HT films. The absorption intensity at 250 nm by UV/vis spectroscopy illustrates that a uniform formation of mixed MWNT/P3HT monolayer into multilayer film was successfully obtained by horizontal deposition. The current-voltage characteristic of the ultra-thin MWNT/P3HT film shows that the current increases linearly with the increasing voltage, which indicates that MWNT/P3HT film forms an ohmic contact with gold. And, the electric current was estimated to be mainly contributed by MWNTs. (C) 2010 Elsevier B.V. All rights reserved.
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  • Potential-Induced Adsorption Behavior of Carboxyl-Terminated Alkanethiol on Au(111) Surfaces

    Liu, Yung-Fang   Chen, Liang-Huei   Yoshimura, Masahiro   Yau, Shueh-Lin   Lee, Yuh-Lang  

    The adsorption and self-assembly behaviors of a carboxyl-group-terminated alkanethiol, 11-mercaptoundecanoic acid (MUA), on Au(111) electrodes in an electrochemical system are studied using in situ scanning tunneling microscopy. The effect of applied potential on the phase evolution of the MUA adlayer is investigated and compared with those reported for alkanethiols with various terminal groups. The results show that the MUA molecules initially adsorb in a lie-down orientation, organizing into ordered domains with a stripe structure. With further adsorption of MUA molecules, the alkyl chains lift off from the substrate, forming a more condensed phase with an arrangement of (root 3 x root 3). This phase evolution is similar to those reported for other alkanethiols. However, the adsorption process of MUA is much slower and a disordered transition phase (gamma phase) exists between the stripe and saturation phases. The gamma phase converts back to the stripe phase when the electrode potential is shifted from 0.2 to 0.4 V, following which the phase evolution cannot proceed further to the saturation phase. These results are contrary to those observed for other alkanethiols and are attributed to the interaction of the terminal COOH group with the substrate at positive potentials. Under the electrode potential, the molecules bind to the substrate via both head and end groups, triggering a lie-down orientation and decreasing the mobility of adsorbed molecules. As a result, the adlayer remains in the stripe phase and further phase evolution is inhibited.
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