One-step hydrothermal synthesis of Ag decorated TiO2 nanoparticles for dye-sensitized solar cell application

Accepted Manuscript One-Step Hydrothermal Synthesis of Ag Decorated TiO2 Nanoparticles for DyeSensitized Solar Cell Application

Yong Xiang Dong, Bo Jin, See Hoon Lee, Xuan Liang Wang, En Mei Jin, Sang Mun Jeong PII:

S0960-1481(18)31506-4

DOI:

10.1016/j.renene.2018.12.062

Reference:

RENE 10937

To appear in:

Renewable Energy

Received Date:

02 October 2018

Accepted Date:

16 December 2018

Please cite this article as: Yong Xiang Dong, Bo Jin, See Hoon Lee, Xuan Liang Wang, En Mei Jin, Sang Mun Jeong, One-Step Hydrothermal Synthesis of Ag Decorated TiO2 Nanoparticles for DyeSensitized Solar Cell Application, Renewable Energy (2018), doi: 10.1016/j.renene.2018.12.062

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ACCEPTED MANUSCRIPT 1

One-Step Hydrothermal Synthesis of Ag Decorated TiO2 Nanoparticles for

2

Dye-Sensitized Solar Cell Application

3 4

Yong Xiang Donga, Bo Jinb, See Hoon Leec, Xuan Liang Wanga, En Mei Jina,*,

5

Sang Mun Jeonga,*

6

aDepartment

Seowon-gu, Cheongju, Chungbuk 28644, Republic of Korea

7 8 9 10 11

of Chemical Engineering, Chungbuk National University, 1 Chungdae-ro,

b

Key Laboratory of Automobile Materials, Ministry of Education, College of Materials Science and Engineering, Jilin University, Changchun 130022, China

cDepartment

of Mineral Resources & Energy Engineering, Chonbuk National University,

Deokjin-dong, Duckjin-gu, Jeonju, Jeonbuk 66414, Republic of Korea

12 13 14

*Corresponding

15

En Mei Jin: [email protected]; Sang Mun Jeong: [email protected]

author:

16 17 18

1

ACCEPTED MANUSCRIPT 19

Abstract

20

Over the past few years, many efforts have been made to develop efficient visible light-

21

activated photovoltaic materials. In this study, the Ag-TiO2 nanoparticles were synthesized

22

by using the hydrothermal method. Ag-TiO2 nanoparticles showed significantly higher

23

visible light absorption and better photovoltaic activity than anatase TiO2. TiO2 nanoparticles

24

were decorated with different concentrations of Ag to improve their photovoltaic properties.

25

All the as-prepared TiO2 and Ag-TiO2 nanoparticles showed a pure anatase crystalline

26

structure. In addition, the Ag-doped nanoparticles showed broader absorption edges (which

27

shifted to higher wavelengths) than the undoped nanoparticles. The solar conversion

28

efficiency (η) of 0.1M Ag-decorated (Ag0.1-TiO2) nanoparticle-based dye-sensitized solar cell

29

(DSSC) was 6.44%, which is ~22% higher than that of the TiO2 nanoparticle-based DSSC (η

30

of 5.05%).

31 32

Keywords: Hydrothermal synthesis, Ag-TiO2, visible light absorption, photovoltaic activity,

33

dye-sensitized solar cell

34 35 36

2

ACCEPTED MANUSCRIPT 37

1. Introduction

38

Dye-sensitized solar cells (DSSCs) as renewable energy source were first reported by Grätzel

39

and O’Regan in 1991 [1]. DSSCs have been extensively investigated because they offer

40

attractive advantages including low cost, easy to make and scale-up, clean renewable energy

41

with less toxic, able to obtain a various colors and light weight [2-5]. Nanostructured titanium

42

dioxide (TiO2) has been studied extensively towing to its unique physical and chemical

43

properties, and potential applications in a wide range of fields including catalysis,

44

photocatalysis, gas sensors, photoluminescence, fuel cells, and solar cells [6‒9]. The unique

45

physical and chemical properties of TiO2 depend on various factors such as its crystalline

46

phase, particle size, and particle shape. For example, TiO2 particles with different crystalline

47

structures exhibit different band gaps (2.98 eV for rutile TiO2, 3.05 eV for anatase TiO2, 3.26

48

eV for brookite TiO2). The band gap of TiO2 determines its photocatalytic activity [8‒11].

49

Various techniques such as the sol-gel, microwave-driven polyol, and hydrothermal methods

50

have been used to synthesize TiO2 nanoparticles [10‒14]. In the hydrothermal method,

51

crystallization occurs in an aqueous solution at relatively low temperatures, less time and

52

high pressures. The hydrothermal reaction also allows a facile synthesis of high-purity

53

crystals.

54

The solar conversion efficiency of DSSCs depends on their open circuit voltage (Voc),

55

photocurrent density (Jsc), and fill factor (FF). The Voc of DSSCs is estimated by the

56

difference between the quasi-Fermi levels of the photoelectrode materials and the redox

57

potential of the electrolyte. The Jsc and FF depend on the adsorption of dye molecules and

58

charge transport. Therefore, in order to improve the photovoltaic properties of TiO2 for DSSC

59

applications, it is imperative to improve its surface area, dye molecular adsorption activity,

60

light harvesting affect, and charge transport. The doping method has been widely used to

3

ACCEPTED MANUSCRIPT 61

synthesize photoelectrode materials for DSSC to improve the charge transfer capability and

62

increase the Voc [15, 16].

63

Gupta et al. [16] doped TiO2 prepared by a modified sol-gel method with 1% Ag and used it

64

as a DSSC photoelectrode. They found that the electron lifetime of the Ag-doped

65

photoelectrode was smaller than that of the undoped photoelectrode (Ag-doped TiO2 = 1.33

66

ms, undoped TiO2 = 2.05 ms). Wu et al. [17] fabricated a Ag-TiO2 composite photoelectrode

67

using a simple approach. They immersed a P25 photoelectrode into a solution containing Ag

68

nanoparticles. This Ag-doping increased the solar conversion efficiency of the photoelectrode

69

from 2.75 to 5.66%. Chang et al. [18] reported that Ag-doped TiO2 shows a porous structure

70

with large surface area and good dye adsorption. This photoelectrode shows a solar

71

conversion efficiency of 6.06 % with controlled film thickness. In addition, the Ag-doped

72

TiO2 nanofiber-added anatase-TiO2 nanoparticle-based (Ag-a-TiNP) photoelectrode showed

73

a smaller electron lifetime than the anatase-TiO2 nanoparticle (a-TiNP) photoelectrode. The

74

Ag-a-TiNP photoelectrode developed in our previous study showed reduced electron

75

recombination, which increased its solar conversion efficiency by about 30% (to 6.13%) [19]

76

In this study, Ag-TiO2 nanoparticles were synthesized by the hydrothermal route. The

77

hydrothermal method is one of the most common and effective synthesis methods for

78

preparation of the nanomaterials with a variety of shapes. The prepared Ag-TiO2

79

nanoparticles exhibited significantly higher visible light absorption and better photovoltaic

80

activity than anatase TiO2 nanoparticles. The TiO2 nanoparticles were decorated with

81

different concentrations of Ag to improve their photovoltaic properties. The as-prepared TiO2

82

and Ag-TiO2 particles showed a pure anatase crystalline structure. The Ag-TiO2 particles

83

showed broader absorption edges (which shifted to higher wavelengths) than the non-doped

84

TiO2 particles.

85

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ACCEPTED MANUSCRIPT 86 87

2. Methods and materials

88

TiO2

89

isopropoxide(TTIP, 99.9%, Aldrich). Typically, TTIP was dissolved in distilled water under

90

stirring for a few minutes and then, NH3 (28-30%, SAMCHUN) was added into the solution.

91

Ag was then doped in a one-step sequence by adding different concentrations (0.05M - 0.2M)

92

of AgNO3 solution. After continuous stirring, the mixture solution was heated in an autoclave

93

at 200oC for 5 h. The obtained precipitate of TiO2 was washed by ethanol and it was vacuum-

94

dried. The as-synthesized TiO2 and Ag-TiO2 was treated by nitric acid to enhance dispersion

95

of particles as reported in our previous report [14]. For the fabrication of photoelectrode for

96

DSSC, TiO2 or Ag-TiO2 powders, acetylacetone (99%, Aldrich), hydroxypropyl cellulose

97

(99%, Aldrich) and distilled water were mixed to prepare a paste. The prepared paste was

98

coated on a fluorine-doped tin oxide substrate (FTO, 8 Ω/cm2, Pilkington), which was

99

subsequently sintered at 450 oC for 0.5 h. Then, the film (active cell area: 0.25 cm2) was

100

immersed in 0.5 mM ethanol solution of N719 dye (cis-bis(isothioxyanato)bis(2,2’-bipyridyl-

101

4,4’-dicarboxylato)-ruthenium(II)bis-tetrabutylammonium) for 5h. The DSSC was assembled

102

by as-prepared TiO2 or Ag-TiO2 photoelectrode and Pt counter electrode as sandwich-type.

103

The electrolyte, 0.5M LiI, 0.05 M I2, 0.5 M 4-tert-butylpyridine, 0.6 M DMPII in 3-

104

methoxypropionitrile was introduced into the cell.

105

The crystal structures and morphologies of the synthesized materials were characterized by

106

X-ray diffraction analysis (XRD, Rigaku, Japan) and field emission transmission electron

107

microscope (FE-TEM, 200KV, JEM 2100F, JEOL). Surface area and pore characterization

108

system (ASAP2020, Micromeritics) were employed to measure the physical properties of

109

nanoparticles. X-ray photoelectron spectroscope (XPS, ESCALAB 210, VG Science) and

110

ultraviolet-visible (UV-Vis) spectrum (S-4100, Scinco) were used to determine the chemical

and

Ag-TiO2

nanoparticles

were

synthesized

by

hydrolysis

of

titanium

5

ACCEPTED MANUSCRIPT 111

states and light absorption ability. Photovoltaic properties of the DSSCs were measured by

112

recoding the current density-voltage characteristics under illumination with a Polaronix K201

113

(McScience, Korea) equipped with a K401 CW150 lamp power supply and an AM 1.5G filter

114

(100 mW/cm2).

115 116 117

3. Results and discussions

118

XRD using Cu Kα radiation was employed to identify the crystalline phases of the

119

synthesized nanoparticles. The XRD data were obtained with a step size of 0.009° in a 2-theta

120

range between 20 - 80°. Fig. 1 shows the the XRD patterns of the TiO2 and Ag-TiO2

121

nanoparticles. All the diffraction peaks of the TiO2 and Ag-TiO2 nanoparticles could be

122

indexed to the crystal structure of the anatase TiO2 phase (space group I41/amd, card no. 21-

123

1276 in the JCPDS database). The sharp and intense peaks at 25.3, 37.9, 48.1, and 53.5°

124

correspond to the (101), (004), (200), and (211) diffraction planes, respectively [20, 21]. The

125

intensity of the (101) peak for the Ag-TiO2 nanoparticles was lower than that for the non-

126

doped TiO2 nanoparticles. It should be noted that at low Ag contents, doping did not affect

127

the anatase crystalline phase; however, it affected the crystallinity of the product. When Ag+

128

or Ag2+ ions are incorporated into the periodic crystal lattice of TiO2 a strain is induced into

129

the system, resulting in the alteration of the lattice periodicity and a decrease in the crystal

130

symmetry.

131

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Ag0.15@TiO2

Intensity (a.u.)

Ag0.10@TiO2 Ag0.05@TiO2

20

132 133

30

40

50

60

116 220 107 215 301

213 204

105 211

200

103 004 112

101

TiO2

70

80

2 - Theta (degree)

Figure 1. XRD patterns of TiO2 and Ag-TiO2 nanoparticles.

134 135

The particle size and morphologies of the TiO2 and Ag0.10-TiO2 nanoparticles were examined

136

by analyzing their FE-TEM images shown in Fig. 2. Both the nanoparticles were pseudo-

137

cube shaped. The average particle size for the TiO2 and Ag0.10-TiO2 nanoparticles was found

138

to be 18 and 14 nm, respectively. Figs. 2 (c) and 2 (d) show the magnified FE-TEM images

139

for the TiO2 and Ag0.10-TiO2 nanoparticles. The TiO2 nanoparticles showed an interplanar

140

spacing of d=0.35 nm corresponding to the (101) plane of anatase TiO2 [22, 23]. The Ag0.10-

141

TiO2 nanoparticles on the other hand, showed an interplanar spacing of d=0.23 nm

142

corresponding to the cubic phase of silver ((111) plane) [24, 25]. This suggests that Ag was

143

successfully incorporated into the TiO2 structure.

144

7

ACCEPTED MANUSCRIPT

(a)

(b) 8.81 nm

12.13 nm

(c)

(d) 0.2313 nm

0.3512 nm 0.3522 nm

145 146

Figure 2. HR-TEM images of (a) TiO2, (b) Ag0.10-TiO2, magnification images of (c) TiO2,

147

and (d) Ag0.10-TiO2 nanoparticles.

148 149

The specific surface area and pore size distribution of TiO2 and Ag-TiO2 nanoparticles were

150

obtained from analysis of the desorption branch of N2 gas isotherms. Fig. 3 shows the

151

nitrogen adsorption-desorption isotherms obtained by the Brunauer-Emmett-Teller (BET)

152

method (for specific surface area) and Barrett-Joyner-Halenda (BJH) pore size distribution

153

curves of the TiO2 and Ag-TiO2 nanoparticles. Both the TiO2 and Ag-TiO2 nanoparticles

154

showed type IV isotherms, which is a characteristic of mesoporous materials (2‒50 nm), with

155

an H2-type hysteresis loop [26]. The specific surface area of the TiO2, Ag0.05-TiO2, Ag0.10-

156

TiO2, Ag0.15-TiO2, and Ag0.20-TiO2 nanoparticles was calculated to be 64.44, 121.95, 139.78,

157

127.94, and 128.40 m2g-1, respectively. These values are significantly higher than the surface

158

area of commercial P25 (51 m2g-1) [27]. The Ag0.10-TiO2 nanoparticles showed the largest 8

ACCEPTED MANUSCRIPT 159

specific surface area. The large surface area of these nanoparticles improved their dye

160

absorption capacity, charge transfer, and solar conversion efficiency. The pore size

161

distribution of the nanoparticles could be calculated from the desorption branches of their N2

162

isotherms using the BJH method (Fig. 3 (b)). The BET results are summarized in Table 1.

163

The Ag-doped TiO2 nanoparticles showed larger pore volume than the TiO2 nanoparticles.

164

Since porous photoelectrodes facilitate the loading of dye molecules on their surface and

165

diffusion of the electrolyte, they significantly affect the photoelectric response of DSSCs [28].

140

150

120 100 80

TiO2

60

Ag0.05TiO2

40

Ag0.10TiO2

20

Ag0.15TiO2 Ag0.20TiO2

0

100

Pore volume (cm3/g*nm)

200

0.6

(a)

160

Surface Area (m2g-1)

Quantity adsorbed (cm3/g STP)

250

TiO2 Ag0.05@TiO2 Ag0.10@TiO2 Ag0.15@TiO2

50

Ag0.20@TiO2

0 0.0

0.2

0.4

0.6

0.8

1.0

(b)

0.5

TiO2 Ag0.05@TiO2 Ag0.10@TiO2

0.4

Ag0.15@TiO2 Ag0.20@TiO2

0.3

0.2

0.1

0.0

10

166

100

Pore diameter (nm)

Relative pressure (P/Po)

167

Figure 3. (a) Nitrogen adsorption-desorption and (b) pore size distribution of TiO2 and Ag

168

decorated TiO2 nanoparticles.

169 170

Table 1. BET results and photon energy of TiO2 and Ag-TiO2 nanoparticles. Samples

TiO2 Ag0.05-TiO2

Ag0.10-TiO2

Ag0.15-TiO2

Ag0.20-TiO2

Surface area

(m²/g)

64.44

121.95

139.78

127.94

128.40

Pore volume

(cm³/g)

0.25

0.29

0.31

0.30

0.31

Pore size

(nm)

9.85

8.06

7.59

8.09

8.28

Photon energy

(eV)

3.22

3.20

3.18

3.12

3.09

171 9

ACCEPTED MANUSCRIPT 172

UV-Vis absorption spectrum is a useful method to determine the light absorption ability of

173

the material and to calculate the photon energy. UV-Vis absorption spectra of the TiO2 and

174

Ag-TiO2 nanoparticles were measured by using a diffuse reflectance mode as shown in Fig.

175

4. All the samples showed strong absorption in the UV region attributing to their band-to-

176

band transitions. The absorption edges of Ag-TiO2 red-shifted slightly with respect to pure

177

TiO2, suggesting that Ag-doping slightly reduced the energy band gap of the nanoparticles. It

178

should be noted that pure TiO2 hardly absorbed light at wavelengths of 430 nm and more. On

179

the other hand, the Ag-TiO2 nanoparticles showed significantly improved capability in the

180

visible spectral region (400‒800 nm). The absorbance of the Ag-TiO2 nanoparticles increased

181

with an increase in the Ag doping content. This can be attributed to the surface plasmon

182

resonance of the nanoparticles i.e., the interference of electromagnetic field with the

183

conduction electrons of silver particles dispersed on the TiO2 matrix [29]. This result suggests

184

that the photovoltaic efficiency of TiO2 can be improved by increasing its light absorption in

185

the visible region by Ag doping.

186

Ag0.05@TiO2 Ag0.10@TiO2 Ag0.15@TiO2

absorbance

Ag0.20@TiO2 TiO2

300

187 188

400

500

600

700

800

Wavelength (nm)

Figure 4. UV-vis absorbance for TiO2 with different values of Ag doping.

189 10

ACCEPTED MANUSCRIPT 190

XPS was used to characterize the oxidation state and the elemental composition. The Ag3d,

191

Ti2p, O1s core level XPS spectra of TiO2 and Ag0.10-TiO2 nanoparticles were shown in Fig. 5.

192

The fully scanned spectra (Fig.5 (a)) showed that Ti, O, and C were present on the surface of

193

the TiO2 and Ag0.10-TiO2 nanoparticles. Chemical bonds corresponding to AgO (Ag2+), Ag2O

194

(Ag+), and Ag (Ag0) were observed at around 367.4, 367.8 eV and 368.2 eV, respectively

195

[30]. However, small Ag peaks were observed in the case of the Ag0.10-TiO2 nanoparticles, as

196

shown in Fig. 5 (b). This can be attributed to the low doping content of these nanoparticles.

197

Chen reported that Ag 3d bond peaks are observed clearly when more than 0.5 wt% of Ag is

198

doped into TiO2 [31]. The presence of elemental C can be ascribed to the contamination of

199

the nanoparticles during the sampling or testing. XPS peak fitting program (PeakFit, Version

200

4, Jandel) was used to analyze the XPS data. The high-resolution Ti 2p spectra of the

201

nanoparticles showed Ti2p3/2 and Ti2p1/2 peaks. The peaks located at 458.56 and 464.31eV

202

can be attributed to Ti4+, while the peaks located at 459.96 and 465.92eV correspond to Ti3+.

203

The Ti2p peak position was almost the same for the Ag0.10-TiO2 and TiO2 nanoparticles.

204

However, the Ti3+ peak area of Ag0.10-TiO2 nanoparticles showed a higher Ti3+ peak area than

205

the TiO2 nanoparticles. This is because in the case of the Ag0.10-TiO2 nanoparticles, Ag

206

accepted electrons from isopropyl radicals (C3H7-) during the hydrothermal reaction and

207

electrons migrated to Ti4+ to form Ti3+ (Ag+e-→Ag-, Ag-+Ti4+→Ti3+) [32]. The O1s XPS

208

peak at 529.82 eV is a characteristic of the lattice oxygen of TiO2 (Ti-O), and the peak

209

located at 531.37 eV can be attributed to the surface hydroxyl groups (OH-).

210

11

ACCEPTED MANUSCRIPT (b) Intensity (a.u.)

Intensity (a.u.)

(a)

0

200

400

O 1s

Ti 2P

Ag 3d

C 1s

Ag0.10@TiO2

TiO2

600

800

360

1000

365

Binding energy (eV)

370

375

380

385

Binding energy (eV)

(c)

Ti 2p3/2

(d)

O 1s

4+

Ti

Ti3+

Ti4+

Ti 2p1/2 Ti3+

Ag0.10@TiO2

Intensity (a.u.)

Intensity (a.u.)

Ti-O

Ti-OH

Ag0.1@TiO2

TiO2

TiO2 456

211

458

460

462

464

466

Binding energy (eV)

468

470

528

530

532

534

Binding energy (eV)

212

Figure 5. (a) The survey spectra, (b) Ag 3d spectra of Ag0.10-TiO2 nanoparticles, (c) Ti 2p,

213

and (d) O 1d core levels of the TiO2 and Ag0.10-TiO2 nanoparticles according to XPS spectra.

214 215

Fig. 6(a) shows the photocurrent density-voltage curves of the nanoparticles synthesized in

216

this study for DSSCs. The solar conversion efficiency (η) of DSSC is given by an equation, η

217

= (Jsc · Voc · FF)/Pin, where Pin is the incident light power (Pin = 100 mW cm−2), Jsc is the

218

photocurrent density, Voc is the open circuit voltage and FF is the fill factor [14]. The Ag-

219

TiO2 nanoparticles showed higher photocurrent density (Jsc) and solar conversion efficiency

220

(η) than the TiO2 nanoparticles. The best photovoltaic properties were shown in The Ag0.10-

221

TiO2 nanoparticles exhibited the best photovoltaic properties owing to their large surface area

222

because of which they could adsorb a large number of dye molecules. Greater absorption of

12

ACCEPTED MANUSCRIPT 223

visible light can improve the utilization of sunlight. However, the Ag-TiO2 nanoparticles

224

showed a slightly higher open circuit voltage (Voc) than the TiO2 nanoparticles. This can be

225

explained with the help of the band edge diagram for Ag-TiO2. The band gap energies of the

226

TiO2 and Ag-TiO2 nanoparticles were calculated using the Tauc’s formula, (αhν) = A(hν –

227

Eg)n, where α is the absorption coefficient, hν is the incident photon energy, A is a constant, n

228

is an integer whose value determines the type of optical transition [33, 34]. Fig. 6(b) shows

229

the (αhv)2 vs. photon energy curve for the TiO2 and Ag-TiO2 nanoparticles. The photon

230

energy of Ag-TiO2 was lower than that of pure TiO2, as can be observed from Table 1. This

231

suggests that the open circuit voltage of DSSCs can be lowered by using a Ag-TiO2

232

photoelectrode. The Voc, Jsc, and FF of Ag0.10-TiO2 were 0.67 V, 17.20 mAcm-2, and 56%,

233

respectively. In particular, Ag doping increased the solar conversion efficiency by 22% (up to

234

6.44%). Table 2 summarizes the photovoltaic parameters obtained in the present work and

235

the previous reports. It is noticeable that the solar conversion efficiency of Ag0.10-TiO2

236

exhibits a higher value than those of the nanoparticles prepared by different methods [16-18].

237 20

(b)

15 2 -1 2 hv) (cm eV)

Current density (mAcm-2)

(a)

10 TiO2 5

Ag0.05@TiO2

TiO2 Ag0.05@TiO2

Ag0.10@TiO2

Ag0.10@TiO2

Ag0.15@TiO2

Ag0.15@TiO2

Ag0.20@TiO2 0 0.0

0.2

Ag0.20@TiO2 0.4

Voltage (V)

0.6

0.8

2.8

3.0

3.2

3.4

3.6

3.8

Photon energy (eV)

238 239

Figure 6. (a) Photocurrent density-voltage curves of DSSCs made of TiO2 and Ag-TiO2

240

photoelectrode, (b) (αhv)2 vs. photon energy plots of TiO2 and Ag-TiO2 nanoparticles.

13

ACCEPTED MANUSCRIPT 241

Table 2. Photovoltaic parameters of DSSCs with variable materials from photocurrent

242

density-voltage curves.

TiO2

Voc (V) 0.69

Jsc FF (mA cm-2) (%) 13.25 55.23

η (%) 5.05

Ag0.05-TiO2

0.67

15.48

56.14

Ag0.10-TiO2

0.67

17.20

Ag0.15-TiO2

0.67

Ag0.20-TiO2

Materials

Synthesis method

Ref.

Hydrothermal

This work

5.82

Hydrothermal

This work

56.92

6.44

Hydrothermal

This work

14.45

56.37

5.46

Hydrothermal

This work

0.67

14.11

56.28

5.32

Hydrothermal

This work

TiO2

0.70

0.63

45

0.14

Sol-gel

[16]

TiO2

0.66

7.34

56.3

2.75

Chemical reduction

[17]

TiO2 (Degussa P25)

0.64

16.62

51

5.55

Commercial

[18]

Ag0.1M-TiO2

0.75

12.29

61.5

5.66

Chemical reduction

[17]

Ag1%-TiO2

0.72

1.07

73

0.40

Sol-gel

[16]

Ag@TiO2 core-shell

0.65

11.3

49.2

3.64

Chemical reduction

[18]

P25:Ag@TiO2=70:30wt%

0.64

18.22

52

6.06

Physical mixture

[18]

243 244 245

4. Conclusions

246

TiO2 and Ag-TiO2 were synthesized using hydrothermal reaction, and their surface area and

247

visible light absorption were improved by Ag-doping. All as-prepared TiO2 and Ag-TiO2

248

particles showed the pure anatase crystalline structure and, in comparison to non-doped TiO2,

249

the absorption edge of Ag-doped nanoparticles were broader and shifted to a higher

250

wavelength. The higher surface and wide visible light absorption region allows us to

251

determine that the Ag0.10-TiO2 nanoparticles-based DSSC gave the best η of 6.44%.

14

ACCEPTED MANUSCRIPT 252

Compared with TiO2-NP photoelectrode based DSSCs (with a value for η of 5.05%), the

253

Ag0.10-TiO2 exhibited an improvement of ~22% in η.

254 255

ACKNOWLEDGEMENTS

256

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the

257

Korea government (MSIT) (2018R1A4A1024691). Also, this research was supported by Basic

258

Science Research Program through the National Research Foundation of Korea (NRF) funded by the

259

Ministry of Education (2017R1D1A1B03028311).

260 261

REFERENCES

262

[1] B. O’Regan, M. Grätzel, A Low-Cost, High-Efficiency Solar Cell Based on Dye-

263

Sensitized Colloidal TiO2 Films, Nature 353 (1991) 737-740.

264

https://doi.org/10.1038/353737a0.

265

[2] L.M. Peter, The Grätzel Cell: Where Next?, J. Phys. Chem. Lett. 2 (2011) 1861-1867.

266

dx.doi.org/10.1021/jz200668q.

267

[3] T.V.S.S.P. Sashank, B. Manikanta, A. Pasula, Fabrication and Experimental Investigation

268

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Highlights  A hydrothermal method has been used to synthesize Ag-doped TiO2 (Ag-TiO2) nanoparticles.  Ag-TiO2 nanoparticles showed high visible light absorption in the visible spectral region.  Ag-TiO2 nanoparticles showed high photocurrent density (Jsc) and solar conversion efficiency (η).  Ag doping increased the solar conversion efficiency by 22% than anatase TiO2.