Plasmonic Effects of Silver Nanoparticles Embedded in the Counter

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Interfaces: Adsorption, Reactions, Films, Forces, Measurement Techniques, Charge Transfer, Electrochemistry, Electrocatalysis, Energy Production and Storage

Plasmonic Effects of Silver Nanoparticles Embedded in the Counter Electrode on Enhanced Performance of Dye-Sensitized Solar Cells Dhanavel Ganeshan, Fengyan Xie, Qingqing Sun, Yafeng Li, and Mingdeng Wei Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b03086 • Publication Date (Web): 25 Apr 2018 Downloaded from http://pubs.acs.org on April 26, 2018

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Plasmonic Effects of Silver Nanoparticles Embedded in the Counter Electrode on Enhanced Performance of Dye-Sensitized Solar Cells Dhanavel Ganeshan, a, b Fengyan Xie, a,b Qingqing Sun, a, b Yafeng Li, a, b and Mingdeng Wei a, b * a

State Key Laboratory of Photocatalysis on Energy and Environment, Fuzhou University, Fuzhou, Fujian 350002, China

b

Institute of Advanced Energy Materials, Fuzhou University, Fuzhou, Fujian 350002, China.

KEYWORDS: plasmonic effects, dye-sensitized solar cell, silver nanoparticles, light harvesting, counter electrode ABSTRACT:

The plasmonic effects of silver (Ag) nanoparticles (NPs) with various

morphologies (sphere, rod, and prism) embedded into the platinum (Pt) counter electrodes (CEs) of dye-sensitized solar cells (DSCs) were systematically investigated. It was showed that the power conversion efficiencies (PCEs) of the incorporated devices are notably improved from 7.60%, for the reference device without Ag NPs, to 8.10%, 8.68%, and 8.55% with Ag nanospheres, nanorods, and nanoprisms devices, respectively. Moreover, the photocurrent and fill factor enhancement is attributed to the better optical and electrical properties of the integrated devices. Among all the NP morphologies studied, Ag nanorods offer the best improvement to the device efficiency as they have longitudinal localized surface plasmon resonance (L-LSPR) and strong scattering effects correlate with in the morphology.

INTRODUCTION 1 ACS Paragon Plus Environment

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Recently, the interest in dye-sensitized solar cells (DSCs) has significantly grown because of their easy manufacture, low cost, and use of low purity components. Since the first report was introduced into DSCs in 1991,1 the research field is developing at a fast pace; however, the power conversion efficiency (PCE) of DSCs is still poor than that of silicon-based solar cells due to the insufficient light within the films.2 To improve the device efficiency of DSCs, a lot of research attempts have been devoted to enhancing the light absorption and improving the charge collection efficiency of photogenerated carriers.3 Generally, the operation of device strongly depends on the different combinations of photoanodes, sensitizers, electrolytes, and counter electrodes (CEs).4-5 Among them, the photoanodes thus have many types of transition metal oxides such as TiO2, ZnO, Nb2O5, and SnO2, the dyes covering ruthenium or zinc based organic molecules, organic-inorganic hybrids of perovskite, and inorganic quantum dots, the novel electrolytes solutions containing an tri-iodide/iodide (I3-/I-) redox couple have been widely investigated, and several research groups have been reported earlier to significantly enhance the DSC efficiency.6-8 However, by employing the well order structures as a photoanodes, new sensitizers dye as a light absorber, good redox couple as a electrolyte solutions, and different structures as a counter electrodes, but the device efficiency of DSCs can only be enhanced marginally.9 One of the most efficient ways to enhance the device efficiency in DSCs through the incorporation of metallic nanoparticles (NPs). The plasmonic effects using noble metal NPs (primarily silver (Ag) and gold (Au)) was recognized as a very promising pathway to improve the light absorption in solar cells.10 Metallic NPs of various morphologies/geometries have been recently investigated for the improvement of DSC efficiency, mainly through the scattering effects at their localized surface plasmon resonance (LSPR) wavelength windows depending on their shape, size, and geometry of the NPs. However, plasmonic NPs introduced in DSCs thus creating some small problems such as back

2 ACS Paragon Plus Environment

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reaction of charge collection efficiency and recombination of charge carriers due to the direct contact between the dye and electrolyte. As a result, various methods have been adopted in DSCs by preventing the back reaction and recombination.11-15 Nonetheless, numerous exciting results have been reported previously the significant improvement of DSCs by embedding the metallic NPs into the photoanodes16-18 and CEs19 of the devices. However, to best of our knowledge, there has been no study on the report of the incorporating of Ag nanorods and nanoprisms into the platinum (Pt) CE.

Figure 1 Device architecture of DSCs with various morphologies of Ag NPs embedded in a counter electrode. In this paper, we compare the scattering and plasmonic effect of NP morphology on device efficiency of DSCs was investigated through incorporation of Ag NPs with various morphologies (sphere, rod, and prism) in the Pt CE. The device structure of plasmonic DSCs is illustrated in Figure 1. To study all the NP morphologies, the rod-shaped Ag NPs is obtained with the highest PCE. This outcome was expected due to the longitudinal-LSPR, strong scattering effects and better optical properties of Ag nanorods as compared to the nanospheres and nanoprisms were verified by a light absorption measurement. The Ag NPs preferred in this study are roughly 40 to 90 nm in dimension, which is optimized size and shape of the NPs applied. We have


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systematically demonstrated the optical and electrical properties, as well as the device performances by employing Ag NPs with various morphologies into the DSCs. EXPERIMENTAL SECTION Materials Fluorine-doped

tin

oxide

coated

on

glass

(FTO,

14

Ω

/sq)

and

(N719,

di-

tetrabutylammoniumcis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4-dicarboxylato)-ruthenium(II)) dye were purchased from Solaronix. TiO2 (P25) was purchased commercially from Degussa AG, Aladdin. Lithium iodide (LiI), iodine (I2), 1,2-dimethyl-3-n-propylimidazolium iodide (DMPImI), ethylene cellulose, titanium tetrachloride (TiCl4), and acetonitrile were all purchased from Sigma-Aldrich Inc (China), respectively, and used as received. Sodium borohydride (NaBH4,

>98%),

silver

nitrate

(AgNO3,

>99%),

trisodium

citrate

(TSC,

>99%),

cetyltrimethylammonium bromide (CTAB, >98%), polyvinylpyrrolidone (PVP, >98%), sodium hydroxide (NaOH, >98%), and ascorbic acid were all purchased commercially and used without any purification. Preparation and Characterization of Metallic Nanoparticles Ag nanospheres were synthesized by a seed-mediated growth method. A synthetic procedure is as follows my previous work:20 a freshly prepared aqueous solutions containing NaBH4 and TSC were mixed and heated to 70 ºC under vigorous stirring for 15 min to make sure a homogenous solution. At the end of 15 min, the required volume of AgNO3 solution was added to the mixture and subsequently, the temperature was further increased to 80 ºC. As the temperature reached 80 ºC, the pH of the solution was adjusted to 10.5 using a 0.1 M NaOH while heating was continued for 1 hr, until a change of color was evident and cooled to room temperature (RT). Finally the Ag nanosphere solution was centrifuged at 12 000 rpm for 15 min to remove the unreacted


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reductants. The precipitate was then re-dispersed into the ethanol and stored at 4 ºC for further use. Ag nanorods were prepared by a seed-mediated growth method. Typically, two steps were included. First, Ag seeds were synthesized based on previously reported.21 A 20 mL solution with a concentration of 0.25 mM AgNO3 and 0.25 mM trisodium citrate in water was prepared under vigorous stirring, 0.6 mL of 10 mM NaBH4 was added all at once, which resulted in the formation of a greenish yellow solution. Stirring was stopped after 30 s. This seed solution was used 2 h after preparation. Second, Ag nanorods were synthesized in a growth solution. CTAB solution (10 mL, 80 mM) was added 0.25 mL of 10 mM AgNO3 solution at 25 °C. To this solution, 0.50 mL of 100 mM ascorbic acid was added. Ascorbic acid as a mild reducing agent changes the growth solution from dark green to colorless. After change the colorless the addition of 0.06ml of the seed solution to the growth solution at RT. Next, 0.10 mL of 1 M NaOH was added to growth solution. NaOH should be added last to obtain the preferred nanorods in decent yield. After addition of NaOH, the solution was gently shaken just enough to mix the NaOH with the growth solution. The color of the solution slowly changed within 1 - 10 min. Finally the solution was centrifuged at a 2000 rpm for rods to remove the excess ligands and CTAB. The Ag precipitate was then re-dispersed into the ethanol for further use. Ag nanoprisms were synthesized by photochemical method and modifying a procedure previously described.22 Ag seeds were prepared by adding 80 μL of freshly prepared and ice-cold 50 mM NaBH4 to an aqueous solution composed of 8 mL of 0.094 mM AgNO3 and 0.28 mM TSC under vigorous stirring for 10 min and then 30 μL of 0.05 M PVP aqueous solution was added in the mixed solution. This solution was stirring vigorously for 30 min and then incubated in a dark at 4°C where it was left undisturbed for 12 h. Then, the bright-yellow solution with Ag seeds was irradiated by a LED for 10 h after adding the 50 μL of 0.5 M NaOH. The solution


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changed to bluish color, indicating that the formation of Ag nanoprisms. The Ag precipitate were purified by washing with aqueous media and centrifuged at a speed of 10 000 rpm for 10 min. Then, the products was put into a vacuum chamber with a under pressure of 10− 3 Pa until the NPs became dry and, finally, the dry Ag nanoprisms were dispersed in ethanol for further use. The Ag NPs with various morphologies were characterized by a transmission electron microscopy (TEM, FEI Tecnai G2 F-20 S-TWIN with a voltage of 200 kV). UV-vis absorption and transmission spectra were obtained at room temperature with the Lambda-950 (PerkinElmer). Atomic force microscopy (AFM) images were performed in air by using a Veeco Multimode NS3A-02 NanoScope III atomic force microscope. Device Fabrication and Measurements The FTO glass plate with a sheet resistance of (14 Ω/sq, Nippon sheet glass) was used for the device fabrication. The FTO glass plates were first cleaned in a detergent, DI water, acetone, and ethanol solution by using an ultrasonic bath for 30 min each, and subsequently dried at 70°C overnight in an oven. Photoanodes were prepared by the screen printing method on the FTO glass using the TiO2 powder (Degussa, P25) with ethyl cellulose (10 wt %) and a solution compose of ethanol and α-terpineol (5 wt %), followed by a calcination at 525 °C for 2 h. After this step, the photoanode films were treated by dipped into a 50 mM TiCl4 aqueous solution at 70 °C for 30 min, rinsed with water and ethanol, and dried with nitrogen. They were then sintered in air at 450 °C for 30 min. Finally, all photoanode films were immersed into a 0.5 mM N719 dye in isopropyl alcohol and acetonitrile (v/v, 1:1) solution for 24 h. For preparation of counter electrodes, Ag NPs with various morphologies solution was sonicated for 5 min before they were mixed with H2PtCl6 (5 mM in isopropanol) solution at a volume of 6:1 by stirring at RT for 5 min. Then, the Pt with and without Ag NPs as a counter electrodes were prepared by coating with a drop of incorporated solution on the cleaned FTO glass followed by heating in air at 400 °C for


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20 min. To avoid the short-circuiting from DSC, the polyethylene spacer with a thickness of 38 μm were inserted between the anode and cathode. A drop of liquid electrolyte solution (electrolyte comprised of 0.6 M 1, 2-dimethyl-3-n-propylimidazolium iodide, 0.1 M LiI, 0.05 M I2, and 0.5 M 4-tertbutylpyridine in acetonitrile) was sandwiched between the working electrode and the counter electrode. The area of the dye-coated TiO2 film was 0.25 cm2. The film thicknesses were evaluated by a Surfcom 130A (Tokyo Seimitsu). The photovoltaic performance of the DSCs was performed with a source meter (Keithley 2400). An AM 1.5 solar simulator (PEC-L11, Peccell, Japan) was used as the light source (100 mW cm-2). The IPCE spectra were recorded by a PEC-S20 (Peccell, Japan). The EIS experiments were measured from the electrochemical work station (IM6, Zahner) and the frequency range from 100 mHz to 1 MHz with an AC signal of 10 mV and a bias DC voltage of -700 mV in the dark. The curves were fitted and analyzed by the Zman software. RESULTS AND DISCUSSION Characterization of Ag NPs with various morphologies In this work, Ag NPs with various morphologies (sphere, rod, and prism) were blended in the counter electrode of DSCs, and the plasmonic effect of various NP morphologies on device efficiency was demonstrated. Ag NPs with various shapes were prepared by seed mediated growth and photochemical method in water solutions (experiment section for more details). The optical properties of the Ag NPs with various morphologies have been described by TEM analysis and UV-Vis spectroscopy. Figure 2 illustrate that the TEM images of Ag NPs with various morphologies (sphere, rod, and prism), respectively. Figure 2a present the TEM result of Ag nanosphere with average diameters around 40 ± 5 nm, Figure 2b shows the TEM analysis of Ag nanorods with the diameter around 20 nm and length is around 90 nm ± 10 nm, and Figure 2c shows the TEM image of triangular Ag nanoprisms with average size is around (~ 60 nm ± 5 nm


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edge length). However, the shape and size of various NP morphologies are well controlled and clearly seen by the TEM measurement.

Figure 2 TEM images of Ag (a) nanospheres, (b) nanorods, and (c) nanoprisms in aqueous medium. The UV−vis absorption spectra of Ag NPs with various morphologies solutions dispersed in water are shown in Figure 3. The absorption peaks for these NPs are placed at 440 and 498 nm for Ag nanospheres and nanoprisms, respectively. Appearance of two absorption peaks, at transverse mode (425 nm) and longitudinal mode (705 nm) is evident of the formation of Ag nanorods.

Figure 3 UV–Vis absorption spectra of Ag nanospheres, Ag nanorods, and Ag nanoprisms suspended in water.


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It is clearly noticed from the Figure 3 that all characteristic peaks for Ag NPs with various morphologies are bathochromically shifted from the corresponding location. Therefore, the addition of these Ag NPs into the counter electrode of DSCs can dramatically improve the light absorption of the incorporated devices by scattering and plasmonic effects. Optical properties of the counter electrode The Ag NPs with various morphologies are embedded in the Pt counter electrode with little aggregation are shown in Figure 4.

Figure 4 Optical transmission spectra of only Pt /Pt films with various shaped Ag NPs. Figure 4 presents the optical transmission spectra of only Pt, Pt with Ag nanospheres, Pt with Ag nanorods, and Pt with Ag nanoprisms. All four substrates show the better transmission with average of over 80% transmittance, indicating that films can maintain the high light transmittance transmittance after coating Pt or Pt with various shaped Ag NPs. The scattering/absorption spectra of only Pt and Pt films with various shaped Ag NPs were also investigated (Figure S2). It is clearly showed that the Ag NPs with varied shaped are mixed very well into the Pt film with no no severe aggregation was observed. Therefore, we could anticipate that the various NP


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morphologies are mostly the similar shape and size into the counter electrode without any changes the morphology.

Figure 5 (a) Topography of AFM images for Pt without Ag NPs (Rq: 9.61 nm), (b) with Ag nanospheres (Rq: 11 nm), (c) with Ag nanorods (Rq: 14.9 nm), and (d) with Ag nanoprisms (Rq: 11.5 nm). Figure 5 displays the AFM images of the Pt film containing Ag NPs with different morphologies (sphere, rod, and prism), respectively. It is clearly observed on the film surfaces significant morphological changes after embedding the Ag NPs. In addition, the root mean squared (Rq) roughness of the only Pt film on FTO plate is calculated at 9.61 nm, although Pt film mixed with various shaped Ag NPs display that the (Rq) roughness is little bigger than that of only Pt film. Hence, as we predict that all the NP morphologies are implanted very well inside the Pt CE so that is the reason changed (Rq) roughness from 9.61 to 11, 14.9, and 11.5 nm, in


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that way. These results suggest that the rough surfaces might induce light trapping at the films and increase the efficiency of the plasmonic devices. This (Rq) roughness size range changed with addition of various shape Ag NPs, so the light absorption could be potentially enhance the incorporated devices by some reasons. First, Ag NP induced by LSPR effect could be increase the light absorption with near-field coupling of electromagnetic fields surrounding to the dye molecules, it is possible in our study as various shaped Ag NPs moderately penetrate (2 - 5 nm) from the counter electrode into the dye molecules. Second, Ag NPs could also induce by scattering effect; it is also boost the optical lengths inside the devices. More importantly, the incorporated device efficiency will dramatically increase by scattering and LSPR effect. In this study, after incorporation of various shaped Ag NPs into the counter electrode may induce the scattering forward and thus improve the absorption light of the N719 molecular dyes with light trapping strategy. Photovoltaic characteristics of DSSCs The photovoltaic characteristics are recorded for reference device with no adding the Ag NPs and incorporated devices with adding the various shaped Ag NPs, are shown in Figures 6 and summarized in Table 1. It is evidently showed from the characteristics that adding the Ag NPs with any morphology into the counter electrode of DSCs improved the PCE as compared to the reference device with no adding the Ag NPs. These judgments are in good agreement while there are few studies previously reported on increase the PCE for devices constructed with adding the metallic NPs into the photoanodes or counter electrodes.16, 18, 19


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Figure 6 (a) J-V curves and (b) normalized IPCE characteristics of DSCs fabricated on Pt counter electrode with and without various shaped Ag NPs. Table 1 Photovoltaic characteristics of DSCs with and without various shaped Ag NPs. Voc

Jsc

FF

PCE

(V)

(mA/cm2)

(%)

(%)

Control

0.746

14.95

68.06

7.60

Sphere

0.763

15.82

68.10

8.22

Rod

0.756

16.74

68.63

8.68

Prism

0.769

16.26

68.39

8.55

Devices

In table 1, we summarize the photovoltaic parameters with reference and plasmonic devices. After blending Ag nanospheres into a counter electrode, open-circuit photovoltage (Voc) increased from 0.746 to 0.763 V, short-circuit photocurrent density (Jsc) increased from 14.95 to 15.82 mA cm-2, fill factor (FF) increased from 68.06 to 68.10%. As a result, PCE improved from 7.60 to 8.22%. Once blending Ag nanoprisms into a counter electrode shows big improvement. Voc further increased to 0.769 V, Jsc enhanced to 16.26 mA cm-2, and FF improved to 68.39 %, leading to a PCE of 8.55%. Very interestingly, device with Ag nanorods showed much better performance, Jsc further increase to 16.74 mA cm-2 and FF improve to 68.63 %, resulting in a


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promising PCE of 8.68 %. It is clearly observed from (Table 1) the enhancements of Jsc and FF leading to the improvement of PCE for addition of Ag NPs with various morphologies. The better contribution is obtained with adding the rod shaped Ag NPs. Therefore, the devices assemble with nanorods give a maximum PCE among various shaped NP studied. Although, these contribution mainly due to the longitudinal shape, optimize size, plasmonic effects, and scattering properties of increased Jsc, thus to improve the device efficiencies of rod shaped NPs are discussed further in details. The Ag nanorods added device showed the highest PCE around 14% as compared to that of reference device assemble under the same optimized conditions. In addition, 8% and 12% enhancements in PCE of the devices with adding the Ag nanospehers and nanoprisms were obtained, respectively. Moreover, a huge improvement in Ag nanorods embedded device shows is not only because of their notable improvement of Jsc (12%) of the device, which is also enhancement in the Voc and FF of the device. Although, the best Voc data are observed from the device with Ag nanoprisms, low Jsc and FF of this device make a nanoprism contribution to the efficiency is much weaker than the device with nanorods. Because of the particles size, shape, plasmonic effects, and scattering efficiencies of various shaped Ag NPs results in decrease of series resistance of the incorporated devices, and mainly increase the light absorption as their have strong ohmic contact within the films and overall device efficiency was improved significantly in DSCs. Among them we studied the various shaped Ag NP incorporated into the counter electrode, Ag nanorods with their longitudinal and transverse shapes have the strongest enhancement in near electromagnetic field and strong scattering around the particles via LSPR effects, especially at the two tips of particle core are extend the light absorption. However, when incorporating various shaped Ag NPs into the counter electrode and the thickness of NPs coated films are increased notably as compared to the


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pure Pt CE, we assume that the anisotropic tips to extending the plasmonic effects into the dye molecules. This broaden leads to an improved the light absorption in N719 dye incorporated devices, and thus enhancement in the DSCs efficiency. Therefore, we expected that the nanorods have a larger size as compared to the thickness of other incorporated CE and that show stronger LSPR effects on wider wavelength to improve the DSCs efficiency much better than the nanospheres and nanoprisms. Moreover, the LSPR properties of various shaped Ag NPs and thickness of Pt CE plays an important role on DSCs efficiency. When the Ag NPs shape or size is close to or bigger than the CE thickness the device efficiency is increased are observed from adding the various shaped Ag NPs into the Pt CE. However, adding the metallic NPs into the Pt CE results in decrease the resistance of DSCs device. As we know that the counter electrode of platinum, has a relatively high resistance and high conductivity. But our study, once we added the different shaped Ag NPs into the CE and then the volume of platinum in CE is decreased, so that is the reason the device resistance will be reduced. DSCs resistance is decreased by adding the various shaped Ag NPs (sphere, rod, and prism), respectively. Due to the decreased resistance for embedded devices results in a considerable enhancement in device efficiency as compared to the reference device with no Ag NPs. One more important reason that influences the device efficiency through light scattering properties, it depends on the size and shape of their particles. For that reason, among all the NPs shaped studied, nanorods have the longer size (~90 nm) are mainly this one have the strong scattering efficiency as compare to spheres (~40 nm) and prisms (~60 nm). In adding to this shape and size of the metallic NPs also influences the scattering efficiency. Recently, Lee and ElSayed was studied and reported by the metallic NP shapes, sizes and scattering efficiency.23 They clearly display that increased in the scattering efficiency through metallic NP shapes changed


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from spheres to different morphologies. In our study also noticed similar results, the scattering property improvement was observed from nanorods device, because they have uniform and longitudinal structure by extending two numbers of tips from NP core. Due to the transverse and longitudinal shapes thus nanorods perform relatively better scattering efficiency compared with nanospheres and nanoprisms under the light trapping method. Incident photon to current efficiency (IPCE) measurement In order to study the spectral response of plasmonic improved DSCs, Incident photon to current conversion efficiency (IPCE) measurement was investigated. Figure 6b shows the IPCE spectra of reference and Ag NPs with various morphologies added devices. The results of Ag nanorods added device showed the largest improvement in the IPCE spectra due to strong light absorption, improved the charge transport, and also enhance the scattering effects. IPCE spectra recorded after adding the various shaped Ag NPs, the incident wavelengths improve significantly from 400 to 710 nm for nanospheres, from 390 to 730 nm for nanorods, and 360 to 720 nm for nanoprisms. The highest IPCE at 550 nm for devices with spherical NPs, nanorods, and nanoprisms were observed. The corresponding IPCE spectra are compared with the reference and incorporated devices, it showed almost overall peaks improvement for nanospheres, nanorods and nanoprisms when selected area of the curves between 300 and 800 nm, especially around the 450 nm and 700 nm. The highest IPCE value is achieved by Ag nanorods, which is a good agreement by seen from Jsc. The notable increases in IPCE are believed and mainly due to the improved light trapping efficiency. As we mentioned before, the absorption peak of Ag nanorods has the maximum overlap as compare to the other shaped NPs (Figure 3), the scattering and plasmonic effects in N719 dye molecules could be strongly attributed, which contributes to the improved light absorption in the surrounding area of Ag nanorods, and thus increased overall Jsc.


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Electrochemical impedance spectroscopy (EIS) analysis To understand the scattering light and plasmonic effect of Ag NPs with various shaped into the counter electrode and performance of device was further optimized, the electrochemical impedance spectroscopy (EIS) of four different types of DSCs were analyzed by a probing method used to investigate the electrical properties in the devices. Figure 7a presents the EIS spectra of Nyquist plots for all tested cells showing two semicircles, and Figure 7b enlarges the small semicircles to been clearly seen. An equivalent circuit of DSCs also depicted in inset of Figure 7a composed of the CE/electrolyte interface and the TiO2/electrolyte interface. The corresponding EIS parameters after fitting were listed in Table 2. From Figure 7b and Table 2, we can find that the small semicircles (RCE) are significantly smaller for the plasmonic devices as compared to the reference device (2.15 < 3.47 < 5.49 < 5.65Ω), which indicates that considerable reduction in charge transfer resistance, resulting in increased Jsc of the plasmonic devices. Interestingly, we can found the slight reduction of R (TiO2/electrolyte) from Figure 7a and Table 2; this might be owed to some other uncertain causes affected by the stronger scattering effect and LSPR effects of Ag/Pt CE.

Figure 7 (a) Nyquist plots of DSCs with and without Ag NPs, and (b) enlarged view of high frequency region (RCE). Inset: The equivalent circuit used for data fitting.


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Table 2 EIS parameters of DSSCs with and without various shaped Ag NPs. Cell

Rs

CCE

RCE

−2

R

C

[Ω]

[Ω ]

[F cm ]

[Ω]

[ F cm−2 ]

Control

6.41

5.65

5.18×10-6

95.56

8.11×10-4

Sphere

8.32

5.49

7.14×10-6

93.69

7.72×10-4

Rod

12.44

2.15

2.95×10-5

80.28

9.93×10-4

Prism

10.18

3.47

6.79×10-6

86.19

8.90×10-4

In the above section are summarized based on our work results, the various morphologies of Ag NPs on the performance of DSCs are verified in terms of optical and electrical properties. Spherical shaped Ag NPs around 40 nm, are present the considerable plasmonic effect and excited by light trap of short-wavelength, which results in a leading improvement in Jsc. Rod shaped Ag NPs around 90 nm length and 20 nm diameter, are exhibit the most powerful plasmonic and scattering effects and also cooperate with more visible light of long-wavelength, which contributes to the highest improvement in Jsc. Triangular shaped Ag NPs around 60 nm edge length, are show the strongest plasmonic effect and light trap in mid-wavelengths, which generates a apparent improvement in Jsc. CONCLUSIONS We have systematically demonstrated the successful utilization of Ag NPs with various morphologies (sphere, rod, and prism) incorporating into the counter electrode for DSCs. Adding the Ag NPs with different shapes of structure resulted in improvement the performance of devices. The enhancement of PCE results from the Ag NP added devices are observed and mostly mostly enhance the Jsc and FF. The performance of devices improved is primarily due to the scattering and plasmonic effects of Ag NPs and their light trapping induce for longer time inside the incorporated film. Among the various morphologies of Ag NPs added in the counter electrode,


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electrode, the device with Ag nanorods confirm the biggest enhancement in PCE, which is due to the considerable improvement in light absorption in the region of ~350-730 nm. Based on our research, Ag nanorods showed superior scattering and LSPR effects as compared to that of nanospheres and nanoprisms, suggesting that Ag nanorods are the useful material for counter electrode in DSCs.


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ASSOCIATED CONTENT Supporting Information Additional data including UV-vis absorption spectra and TEM images of

Plasmonic Effects of Silver Nanoparticles Embedded in the Counter

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