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Dual Functional Polymer Interlayer for Facilitating Ion Transport and Reducing Charge Recombination in Dye-Sensitized Solar Cells Ying-Chiao Wang, Shao-Sian Li, Cheng-Yen Wen, Liang-Yih Chen, Kuo-Chuan Ho, and Chun-Wei Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b11658 • Publication Date (Web): 18 Nov 2016 Downloaded from http://pubs.acs.org on November 19, 2016

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ACS Applied Materials & Interfaces

Dual Functional Polymer Interlayer for Facilitating Ion Transport and Reducing Charge Recombination in Dye-Sensitized Solar Cells Ying-Chiao Wang, Shao-Sian Li, Cheng-Yen Wen, Liang-Yih Chen,*,¶ Kuo-Chuan Ho‡ and Chun-Wei Chen*,



Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan.

¶

Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10617, Taiwan.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan

RECEIVED DATE

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ABSTRACT. Dye-sensitized solar cells (DSSCs) present low-cost alternatives to conventional wafer-based inorganic solar cells and have remarkable power conversion efficiency. To further enhance performance, we propose a new DSSC architecture with a novel dual-functional polymer interlayer that prevents charge recombination and facilitates ionic conduction, as well as maintaining dye loading and regeneration. Poly (vinylidene fluoride-trifluoroethylene) (p(VDF-TrFE)) was coated on the outside of a dye-sensitized TiO2 photoanode by a simple solution process that did not sacrifice the amount of adsorbed dye molecules in the DSSC device. Light intensity modulated photocurrent and photovoltage spectroscopy revealed that the proposed p(VDF-TrFE)coated anode yielded longer electron lifetime and improved the injection of photogenerated electrons into TiO2, thereby reducing the electron transport time. Comparative cyclic voltammetry and UV-visible absorption spectroscopy based on a ferrocene–ferrocenium external standard material demonstrated that p(VDF-TrFE) enhanced the power conversion efficiency from 7.67% to 9.11%. This dual functional p(VDF-TrFE) interlayer is a promising candidate for improving the performance of DSSCs and can also be employed in other electrochemical devices.

KEYWORDS. p(VDF-TrFE) copolymer, recombination, solution process, dyesensitized solar cell, ionic conductivity


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INTRODUCTION Dye-sensitized solar cells (DSSCs) have attracted great interest owing to their promise for fabricating low-cost and remarkable power conversion efficiency of photovoltaic devices as an alternative to conventional wafer-based inorganic solar cells.1-4 The most commonly photoanode of a DSSC comprises a mesoporous wide bandgap semiconductor, typically titanium dioxide (TiO2), adsorbed with a monolayer of the ruthenium (Ru) complex sensitizers.5 Upon excitation of Ru-based dyes, the electrons in the excited states of dye molecules are injected into the conduction band of the TiO2 photoanode and transport through TiO2 photoanode toward the collection transparent conductive oxide (TCO) substrates. On the other hand, the oxidized dye (S+) is regenerated by the redox electrolyte species (I-) or recaptures the electrons from the conduction band of TiO2 photoanode. To complete the whole process, electrons may transport toward the counter electrode (CE) and transfer into the electrolyte for reducing triiodide (I3-) ions.1, 6, 7 However, the recombination process usually take place simultaneously at several interfaces when electrons are transporting toward the photoanode, such as FTO/TiO2, FTO/electrolytes, dye/electrolytes and TiO2/electrolytes.8 In past few years, several strategies have been proposed to reduce the occurrence of recombination processes to further improve the power conversion efficiencies of DSSCs.9-12 Because recombination at the interface at TiO2/electrolytes is found to be the predominant process among the above mentioned multiple recombination routes,5, 6, 8, 13, 14 many researchers coated an ultrathin metal oxide layer outside the surfaces of TiO2 photoanode by using dip-coating metal alkoxy precursors or atomic layer deposition (ALD).15-18 The ultrathin metal oxide layer could be regarded as blocking layer to reduce the occurrence of recombination process at the interfaces of TiO2 photoanode/electrolytes. However, the device structure using the passivation of the TiO2 photoanode with a metal oxide layer could inevitably affect the adsorption of dye molecules on the surface of the passivation layer and deteriorate the electron injection rate.15 To overcome this problem, one possible strategy is to deposit a blocking layer onto the dye-adsorbed TiO2 photoanode without sacrificing the amount of adsorbed dye molecules. Nevertheless, the critical issue for the insertion of an interlayer layer on a dye-adsorbed TiO2 photoanode is the possible reduction of the dye regeneration rate at the interface of TiO2 photoanode/dyes/electrolytes 3 ACS Paragon Plus Environment


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due to high ion transfer resistance between electron donor I- and oxidized dye (S+). Therefore, it will be technologically favorable to pursue a novel interlayer layer which has dual functions of not only preventing charge recombination but also maintaining dye loading/regeneration for further enhancing the performance of DSSCs. In previous studies, Hsu et al. and M. Grätzel et al. ever used polyvinylidene difluoride (PVDF)-based polymer electrolyte in electrochromic (EC) devices and DSSCs, such as poly(vinylidene

fluoridehexafluoropropylene)

(p(VDF-HFP))

and

poly

(vinylidene

fluoridetrifluoroethylene) (p(VDF-TrFE)), due to its ionic conduction characteristics.19, 20 The average values of the polymer electrolyte were found to be 6.26x10-6 S/cm.21 In this work, p(VDF-TrFE) was employed as interlayer to cover on the outside of dye-sensitized TiO2 photoanode and to study the influence on the performance of DSSCs. EXPERIMENTAL SECTION Preparation of p(VDF-TrFE) modified photoanodes. Poly (vinylidene fluoride-trifluoroethylene), p(VDF-TrFE), from Solvay, molecular weight is 350,000 g/mol), containing the molar ratio of 70 % vinylidene fluoride and 30 % trifluoroethylene, was dissolved in dimethyl sulfoxid (DMSO) with a concentration of 500 µg/mL by magnetic stirring at 50 oC until a homogeneous solution was obtained. Next, p(VDF-TrFE) solution was spin-coated onto the N719 dye- sensitized TiO2 photoanode at 6000 rpm for 1 minute to fabricate p(VDF-TrFE) modified dye-sensitized TiO2 photoanodes. Dye-sensitized solar cell fabrication. The handmade TiO2 paste prepared as previous reports was coated on the FTO glass by using a doctor-blade method as structural layer. The coated FTO glass was annealed at 450 oC for 30 min. After coating and annealing, light scattering layer consisting of TiO2 nanoparticles with 300 nm was coated on top of structural layer, and the anneal process was performed in the same way. The working area of 0.16 cm2 was soaked overnight in dye solution, containing 0.3 mM cis-Bis(isothio-cyanato)-bis(2,2'-bipyridyl-4,4'-dicarboxylato)

ruthenium(II)bis-tetrabutylammonium

dye (so called N719) in acetonitrile/tert-butanol (v/v = 1:1). In addition, Pt was sputtered on the ITO glass as the counter electrode. The dye-sensitized solar cell was assembled with the working electrode (with or

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w/o p(VDF-TrFE coated TiO2 photoanode) and the counter electrode.

A distance of 25 μm was

maintained between the two electrodes by using an ionomer resin (Surlyn®, SX1170-25) as the spacer. Then the electrolyte was injected into the space separated by the Surlyn® via a capillary effect. The electrolyte contained 0.6 M 1,2-dimethyl-3-propylimidazolium iodide (DMPII), 0.1 M LiI, 0.05 M I2, and 0.5 M 4-tert-butylpyridine (4-tBP, 96%) in 3-methoxypropionitrile (MPN, 99%). Characterizations and measurements. The transmission electron microscopy (TEM) investigation was performed in a 200 kV FEI Tecnai F20 microscope, equipped with the Gatan Tridiem electron energy loss spectrometer. The energy-filtered TEM (EFTEM) images were formed with electrons that have a specific energy loss, with respect to the absorption edge of the atomic inner shell, for chemical mapping. The TEM specimens were prepared using the FEI Helios 600i focused-ion beam system. The catalytic ability of the photoanodes measured using steady-state voltammograms, cyclic voltammetry (CV), which were recorded by a potentiostat/galvanostat (PGSTAT 30, Autolab, Eco-Chemie, Netherlands). The carrier transfer/transport properties were analyzed by electrochemical workstation with a light emitting diode (White (Neutral)) for the studies of intensity-modulated photocurrent (IMPS) and intensitymodulated photovoltage spectroscopy (IMVS). The current density (J) and voltage (V) of the cell was measured under AM 1.5 G simulation sunlight, which as produced by a 150 W Class A Solar Simulator (Newport Inc.) with an illumination intensity of 100 mW/cm2. The incident photon-to-electron conversion efficiency (IPCE) was measured by using a Xe lamp in combination with a monochromator (Oriel Inc.). UV/Vis transmission spectra were obtained by using Cary 500 UV/Vis/NIR spectrophotometer. RESULTS AND DISCUSSION In this work, we would like to propose a new device architecture where the polymer interlayer of poly (vinylidene fluoride-trifluoroethylene) (p(VDF-TrFE)) was coated on the outside of the dyesensitized TiO2 photoanode by a simple solution process as shown in Figure 1. The unique advantage of this device structure is that the deposition of an interlayer layer onto the dye-sensitized TiO2 photoanode does not sacrifice the amount of adsorbed dye molecules in the DSSC device, unlike the conventional



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technique with a largely reduced amount of adsorbed dye molecules on the surface of the blocking layer.22 p(VDF-TrFE) copolymer, which has its advantages of chemical inertness, low fabrication temperature, photostability and permanent ferroelectric properties, has been widely studied for applications as piezoelectric and pyroelectric devices.23-26 The ferroelectric properties originated from the large difference in the electronegativity between fluorine, carbon and hydrogen and the molecular dipoles attached perpendicular to the chain axes as shown in Figure. S1, where the dipole moment in the β-phase of p(VDF-TrFE) points from the fluorine side to the hydrogen side along the applied electric field spontaneously.27-29 In addition, p(VDF-TrFE) has been used as solid polymer electrolyte (SPE) in solidstate batteries27-30 and other electrochemical devices23 due to its high ionic conductivity. p(VDF-TrFE) has been used as a SPE in the lithium ion (Li-ion) battery and showed its ionic conductivity at room temperature to achieve 2.6 mS/cm in organic electrolyte.30

Figure 1. A simple solution-process was used to fabricate the conformal p(VDF-TrFE) interlayer onto dye-sensitized TiO2 photoanodes to efficiently reduce recombination without affecting carrier transfer for dye-sensitized solar cells. Figure 2(a) shows the zero-loss energy-filtered transmission electron microscopy (EFTEM) image of a p(VDF-TrFE) polymer interlayer coated on the dye-sensitized TiO2 photoanode with a thickness of approximately 18 nm. The elemental mapping images of carbon K edge and titanium L2,3 edge in Figures 2(b) and 2(c) provide the individual distributions of carbon and titanium in the dye-sensitized TiO2 photoanode respectively, indicating that a p(VDF-TrFE) thin film could be uniformly coated on the 6 ACS Paragon Plus Environment

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surface of the TiO2 photoanode as shown in Figure 2(d). For comparison, the EFTEM image of the pristine TiO2 nanoparticles without the coating of a p(VDF-TrFE) layer was also obtained, where a small amount of carbon residues is only found at the surface of the TiO2 nanoparticles (Figure S2 in supporting information). Figure 2(e) shows the absorption spectra of the adsorbed dyes on the TiO2 photoanodes with and without a coated p(VDF-TrFE) polymer interlayer. The inset of Figure 2(e) exhibits a well-defined excitonic absorption peak of p(VDF-TrFE) with a band gap value of 3.76 eV. The amounts of adsorbed dye molecules on the TiO2 photoanodes with and without a coated p(VDF-TrFE) polymer interlayer are nearly identical, indicating that the deposition of an interlayer layer onto the dye-sensitized TiO2 photoanode does not sacrifice the amount of adsorbed dye molecules in the DSSC device, in contrast to the conventional device structure where the amount of adsorbed dye molecules on the surface of the blocking layer may be largely reduced.22

Figure 2. Energy-filtered transmission electron microscopy (EFTEM) images: (a) zero-loss, (b) C K-edge, (c) Ti L2,3-edge and (d) composited image. (e) UV-vis absorption spectra of the TiO2/dye and TiO2/dye/p(VDF-TrFE) photoanodes. The inset is the UV-vis absorption spectrum of p(VDF-TrFE) film.



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To further understand the role of p(VDF-TrFE) on the performance of DSSCs, the energy levels of high occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were firstly characterized by cyclic voltammetry (CV) and UV-visible absorption spectroscopy. Herein, the CV measurement was performed to obtain the LUMO energy level of p(VDF-TrFE) as shown in Figure 3(a). Comparing to the potential of an external standard material (ferrocene/ferrocenium couple, Fc/Fc+), and then calculating the formal LUMO level of p(VDF-TrFE) (-3.57 eV) with the empirical relation.31  red  E LUMO  e  E onset  vs.Ag/AgCl   E onset  Fc/Fc vs. Ag/AgCl     4.8 eV   

(1)

Figure 3. (a) Cyclic voltammetry (CV) analysis for p(VDF-TrFE) and (b) the corresponding energy levels of the dye-sensitized solar cell. The corresponding HOMO energy level of p(VDF-TrFE) was obtained by subtracting the band gap (Eg), resulting from the excitonic absorption peak as shown in the inset of Figure 2(e). The corresponding energy levels of the p(VDF-TrFE) coated dye-sensitized TiO2 photoanode and electrolyte are summarized in Figure 3(b). It is found that the LUMO of p(VDF-TrFE) is higher than the conduction band of the TiO2 photoanode, which may effectively prevent the carrier recombination between photogenerated electrons in dye molecules and redox couples. The current density-voltage (J-V) characteristics of DSSCs without and with the insertion of various thickness p(VDF-TrFE) interlayer coated on dye-sensitized TiO2 photoanode under standard AM 1.5 simulated illumination of 100 mW/cm2 are shown in Figure 4(a) and the parameters of the photovoltaic performances of the DSSC devices are summarized in Table 1. For the


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reference cell which consists of a pristine dye-sensitized TiO2 photoanode, the photovoltaic performance of the DSSC device exhibits an open circuit voltage (Voc) of 0.73 V, a short circuit current density (Jsc) of 15.23 mA/cm2 and an fill factor (FF) of 0.69, yielding a power conversion efficiency (PCE) of η=7.67 %. By contrast, the DSSC device consisting of p(VDF-TrFE) coated dye-sensitized TiO2 photoanode with a thickness of 12 nm exhibits a PCE of 9.11 %, with Voc, Jsc and FF of 0.75 V, 16.92 mA/cm2 and 0.72, respectively. When further increasing the thickness of p(VDF-TrFE) interlayer from 12 nm to 18 nm and 30 nm, the PCEs of DSSCs decrease from 9.11% to 6.71% and 5.60%, respectively. We also try to reduce the thickness of the p(VDF-TrFE) interlayer to less than 12 nm for improving the performance of DSSC; however, the corresponding PCE is lower than that of DSSC consisting of a pristine dye-sensitized TiO2 photoanode due to non-complete coverage of p(VDF-TrFE) coating (not shown here). Accordingly, the optimal device consisting of a p(VDF-TrFE) interlayer with 12 nm on dye-sensitized TiO2 photoanode exhibits a nearly 19 % enhancement of the PCE with increased Voc, Jsc and FF for the device compared to the device consisting of a pristine dye-sensitized TiO2 photoanode. The result indicated that the p(VDFTrFE) interlayer with an optimal thickness coated on a dye-sensitized TiO2 photoanode may play a significant role to enhance the PCE of the DSSC device. To demonstrate the reproducibility, the statistic of PCE value of DSSCs with 12 nm p(VDF-TrFE) was shown in Figure S3 and the average PCE is ca. 8.8% (32 DSSCs were analyzed for statistics). The result indicates that this process is reproducible when 12 nm p(VDF-TrFE) film is employed as interlayer on the photoanode. In addition, the corresponding incident photon-to-electron conversion efficiencies (IPCE) of DSSCs are shown in Figure 4(b). The IPCE for the device consisting of a 12 nm p(VDF-TrFE) interlayer coated on the dye-sensitized TiO2 photoanode reaches ~70%, higher than that of the pristine device.



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Figure 4. (a) Current density-voltage (J-V) characteristics measured under AM 1.5 illumination of 100 mW cm-2. (b) Incident photon-to-electron conversion efficiencies (IPCEs). Table 1. Performances of introducing p(VDF-TrFE) onto dye-sensitized TiO2 photoanodes under AM 1.5 illumination of 100 mWcm-2 Working electrode

Voc (V)

Jsc (mA/cm2)

FF (%)

 (%)

Pristine

0.73

15.23

0.69

7.67

p(VDF-TrFE)-12 nm

0.75

16.92

0.72

9.11

p(VDF-TrFE)-18 nm

0.73

13.14

0.70

6.71

p(VDF-TrFE)-30 nm

0.67

12.89

0.65

5.60

To further understand the role of p(VDF-TrFE) on the performance of DSSC, the activity of dye regeneration of dye-sensitized TiO2 photoanode after coating a p(VDF-TrFE) interlayer is analyzed by steady-state voltammogram. The current density (J)-bias (U) curves were measured in the dark and under AM 1.5 illumination of 100 mW/cm2. The devices consisted of a two-electrode structure, i.e., working electrode (WE)/electrolyte/Pt, where two electrodes were separated between an ionomer resin spacer (Surlyn®, SX1170-25). Here, pristine or p(VDF-TrFE) coated dye-sensitized TiO2 photoanode was regarded as working electrode and Pt was regarded as counter electrode. Figure 5(a) shows the dye regeneration activity of WEs with and without coating of a p(VDF-TrFE) interlayer measured in the dark where the anodic branches indicated oxidation of I- ions by the WEs. The current density of the WE consisting of a p(VDF-TrFE) interlayer could achieve 54 mA/cm2, which was higher than 32 mA/cm2 of the pristine dye-sensitized TiO2 photoanode. The result indicated that the dye regeneration activity could 10 ACS Paragon Plus Environment

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be further enhanced after p(VDF-TrFE) coating due to its excellent ionic conductivity.24, 26, 30, 32 For comparison, we also fabricated two WEs consisting of a blocking layer with a thickness of 5 nm based on two kinds of metal oxides, TiO2 and alumina (Al2O3) deposited on the dye-sensitized TiO2 photoanode by atomic layer deposition (ALD). Figure 5(b) shows the corresponding characteristic curves of dye regeneration activities of WEs consisting of a pristine dye-sensitized TiO2 photoanode, a p(VDF-TrFE) coated dye-sensitized TiO2 photoanode and two metal-oxide coated dye-sensitized TiO2 photoanodes as the devices were under light illumination. (AM 1.5, 100 mW/cm2) The device consisting of the p(VDFTrFE) interlayer with an optimal thickness of 12 nm was found to show an enhanced current density (124 mA/cm2) compared to 73 mA/cm2 of the cell consisting of a pristine dye-sensitized TiO2 photoanode. As the p(VDF-TrFE) interlayer was replaced by 5 nm TiO2 or Al2O3 thin films, the current densities were low, indicating the poor electrochemical activities for dye regeneration. Although TiO2 or Al2O3 can be regarded as an effective blocking layer to prevent charge recombination, the poor ionic conduction behavior may largely hinder the dye regeneration. By contrast, the deposition of a p(VDF-TrFE) interlayer on a dye-sensitized TiO2 photoanode, which exhibits the unique dual functions of reducing charge recombination and facilitating ionic conduction, may result in the significantly enhanced PCE of the DSSC.

Figure 5. (a) Steady-state voltammograms corresponding to pristine and p(VDF-TrFE) coated dyesensitized TiO2 photoanodes using the electrochemical devices of WE/electrolyte/Pt-CE in the dark. Scan rate: 50 mV s-1. (b) Steady-state voltammograms corresponding to various WEs based electrochemical devices (WE/electrolyte/Pt-CE) under AM 1.5 illumination of 100 mW cm-2. Scan rate: 50 mV s-1. 11 ACS Paragon Plus Environment


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Next, the electron transport and recombination behaviors of the cells consisting of pristine and p(VDF-TrFE) coated dye-sensitized TiO2 photoanodes were further investigated by light intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) under white LED with variable intensities from 20 to 40 mW/cm2. Figure 6 represents the dependence of electron transport time (d) and electron recombination lifetime (n) as a function of light intensity. Clearly recognized are the power law dependences of the d and n on light intensity, which are in accordance with the well-known trapping/detrapping model to describe electron transport/recombination in DSSCs.8, 33 The d is shorter at higher light intensity because more deep traps are filled and then more electrons transport through trapping/detrapping sites around shallower energy levels.34 From IMVS analysis, we can also obverse that DSSC with p(VDF-TrFE) coated dye-sensitized TiO2 photoanode can reduce the occurrence of recombination to obtain long electron lifetime. When p(VDF-TrFE) is employed as an interlayer to coat on the outside of dye-sensitized TiO2 photoanode, it can reduce effectively the occurrence of recombination to increase the concentration of carriers (electrons) inside the TiO2 photoanodes. More electrons can fill-in the deep trapping sites to reduce the occurrence of trapping/detrapping events during transportation. Therefore, we can obtain short electron transport time when a p(VDF-TrFE) interlayer was used. In addition, the holes generated under light illumination can also be effectively removed by I- ions because p(VDF-TrFE) also exhibits good ionic conduction behaviour. Because the deposition of an interlayer of p(VDF-TrFE) onto the dye-adsorbed TiO2 photoanode does not sacrifice the amount of adsorbed dye molecules in the DSSC device, the deposition of the p(VDF-TrFE) interlayer with an optimal thickness has the unique dual functions of not only preventing charge recombination but also and maintaining dye loading/regeneration for further enhancing the performance of DSSCs.


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Figure 6. Carrier transport time and electron recombination lifetime versus light intensity measured by IMPS and IMVS for the DSSC devices with pristine and various thickness of P(VDF-TrFE) film coated dye-sensitized TiO2 photoanodes. CONCLUSIONS In conclusion, a new device architecture where a polymer interlayer of p(VDF-TrFE) was coated on the outside of the dye-adsorbed TiO2 photoanode of a DSSC by a simple solution process has been proposed. The enhanced power conversion efficiencies from 7.67% to 9.11% with the insertion of a p(VDF-TrFE) interlayer can be achieved, where the insertion of the dual functional p(VDF-TrFE) polymer interlayer on the dye-adsorbed TiO2 photoanode can act the role to reduce charge recombination and facilitate ionic conduction in DSSCs. The dual functional polymer interlayer could be regarded as a promising candidate for improving the performance of DSSCs and also be employed in the other electrochemical devices in the future. ASSOCIATED CONTENT AUTHOR INFORMATION Corresponding author The author(s) to whom correspondence should be addressed. Chun-Wei Chen ([email protected]) and Liang-Yih Chen ([email protected]) ACKNOWLEDGMENT



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We are grateful for the financial support provided by Minster of Science and Technology (MOST), Taiwan (Project No. 104-2112-M-003) and NTU-Triangle project. National Science Council under Contract no. NSC 100-2119-M-002-020- and NSC 100-2628-M-002-013- MY3. REFERENCES 1.

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Engineering of TiO2 Nanocrystals: Improve the Efficiency and Stability of Dye-Sensitized Solar Cells. Adv. Mater. 2003, 15, 2101-2104. 10. Huang, S. Y.; Schlichthörl, G.; Nozik, A. J.; Grätzel, M.; Frank, A. J., Charge Recombination in Dye-Sensitized Nanocrystalline TiO2 Solar Cells. J. Phys. Chem. B 1997, 101 (14), 2576-2582. 11. Wang, P.; Zakeeruddin, S. M.; Comte, P.; Charvet, R.; Humphry-Baker, R.; Grätzel, M., Enhance the Performance of Dye-Sensitized Solar Cells by Co-grafting Amphiphilic Sensitizer and Hexadecylmalonic Acid on TiO2 Nanocrystals. J. Phys. Chem. B 2003, 107 (51), 14336-14341. 12. Zhang, Z.; Evans, N.; Zakeeruddin, S. M.; Humphry-Baker, R.; Grätzel, M., Effects of ωguanidinoalkyl Acids as Coadsorbents in Dye-Sensitized Solar Cells. J. Phys. Chem. C 2007, 111 (1), 398-403.


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13. Daeneke, T.; Mozer, A. J.; Kwon, T.-H.; Duffy, N. W.; Holmes, A. B.; Bach, U.; Spiccia, L., Dye Regeneration and Charge Recombination in Dye-Sensitized Solar Cells with Ferrocene Derivatives as Redox Mediators. Energy & Environmental Science 2012, 5 (5), 7090-7099. 14. Gregg, B. A.; Pichot, F.; Ferrere, S.; Fields, C. L., Interfacial Recombination Processes in DyeSensitized Solar Cells and Methods to Passivate the Interfaces. J. Phys. Chem. B 2001, 105 (7), 14221429. 15. Ito, S.; Liska, P.; Comte, P.; Charvet, R.; Pechy, P.; Bach, U.; Schmidt-Mende, L.; Zakeeruddin, S. M.; Kay, A.; Nazeeruddin, M. K.; Gratzel, M., Control of Dark Current in Photoelectrochemical (TiO2/I-I3-) and Dye-Sensitized Solar Cells. Chem. Commun. 2005, (34), 4351-4353. 16. Palomares, E.; Clifford, J. N.; Haque, S. A.; Lutz, T.; Durrant, J. R., Slow Charge Recombination in Dye-Sensitised Solar Cells (DSSC) Using Al2O3 Coated Nanoporous TiO2 Films. Chem. Commun. 2002, (14), 1464-1465. 17. Palomares, E.; Clifford, J. N.; Haque, S. A.; Lutz, T.; Durrant, J. R., Control of Charge Recombination Dynamics in Dye Sensitized Solar Cells by the Use of Conformally Deposited Metal Oxide Blocking Layers. J. Am. Chem. Soc. 2003, 125 (2), 475-482. 18. Lin, C.; Tsai, F.-Y.; Lee, M.-H.; Lee, C.-H.; Tien, T.-C.; Wang, L.-P.; Tsai, S.-Y., Enhanced Performance of Dye-Sensitized Solar Cells by an Al2O3 Charge-Recombination Barrier Formed by LowTemperature Atomic Layer Deposition. J. Mater. Chem. 2009, 19 (19), 2999-3003. 19. Chih-Yu Hsu, K.-M. L., Jen-Hsien Huang, K.R. Justin Thomas, Jiann T. Lin, Kuo-Chuan Ho, A Novel Photoelectrochromic Device with Dual Application Based on Poly(3,4-alkylenedioxythiophene) Thin Film and an Organic Dye. J. Power Sources 2008, 185, 1505-1508. 20. Peng Wang, S. M. Z., Jacques E. Moser, Mohammad K. Nazeeruddin,Takashi Sekiguchi AND Michael Gratzel, A Stable Quasi-Solid-State Dye-Sensitized Solar Cell with an Amphiphilic Ruthenium Sensitizer and Polymer Gel Electrolyte. Nat. Mater. 2003, 2, 402-407. 21. Nguyen, C. A.; Xiong, S.; Ma, J.; Lu, X.; Lee, P. S., Toward Electrochromic Device Using Solid Electrolyte with Polar Polymer Host. J. Phys. Chem. B 2009, 113 (23), 8006-8010. 22. Law, M.; Greene, L. E.; Radenovic, A.; Kuykendall, T.; Liphardt, J.; Yang, P., ZnO−Al2O3 and ZnO−TiO2 Core−Shell Nanowire Dye-Sensitized Solar Cells. J. Phys. Chem. B 2006, 110 (45), 2265222663. 23. Wilson A. Gazotti Jr.; Giuseppe Casalbore-Miceli; Alessandro Geri; Paoli, M.-A. d., Solid-State Electrochromic Device Based on Two Optically Complementary Conducting Polymers. Adv. Mater. 1998, 10, 60-64.



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Table Of Contents



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Figure 1. A simple solution-process was used to fabricate the conformal p(VDF-TrFE) interlayer onto dyesensitized TiO2 photoanodes to efficiently reduce recombination without affecting carrier transfer for dyesensitized solar cells.

297x123mm (116 x 116 DPI)


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Figure 2. Energy-filtered transmission electron microscopy (EFTEM) images: (a) zero-loss, (b) C K-edge, (c) Ti L2,3-edge and (d) composited image. (e) UV-vis absorption spectra of the TiO2/dye and TiO2/dye/p(VDFTrFE) photoanodes. The inset is the UV-vis absorption spectrum of p(VDF-TrFE) film. 338x165mm (150 x 150 DPI)



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Figure 3. (a) Cyclic voltammetry (CV) analysis for p(VDF-TrFE) and (b) the corresponding energy levels of the dye-sensitized solar cell.

240x91mm (150 x 150 DPI)


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Figure 4. (a) Current density-voltage (J-V) characteristics measured under AM 1.5 illumination of 100 mW cm-2. (b) Incident photon-to-electron conversion efficiencies (IPCEs). 257x95mm (150 x 150 DPI)



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Figure 5. (a) Steady-state voltammograms corresponding to pristine and p(VDF-TrFE) coated dye-sensitized TiO2 photoanodes using the electrochemical devices of WE/electrolyte/Pt-CE in the dark. Scan rate: 50 mV s-1. (b) Steady-state voltammograms corresponding to various WEs based electrochemical devices (WE/electrolyte/Pt-CE) under AM 1.5 illumination of 100 mW cm-2. Scan rate: 50 mV s-1. 263x96mm (150 x 150 DPI)


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Figure 6. Carrier transport time and electron recombination lifetime versus light intensity measured by IMPS and IMVS for the DSSC devices with pristine and various thickness of P(VDF-TrFE) film coated dye-sensitized TiO2 photoanodes.

171x130mm (150 x 150 DPI)


Dual Functional Polymer Interlayer for Facilitating ... - ACS Publications

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