research article enhanced efficiency of dye-sensitized

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 760685 6 pageshttpdxdoiorg1011552013760685

Research ArticleEnhanced Efficiency of Dye-Sensitized Solar Cell byHigh Surface Area Anatase-TiO2-Modified P25 Paste

Mengmei Pan1 Niu Huang2 Xingzhong Zhao2 Jun Fu1 and Xiaoli Zhong1

1 College of Physics and Electronic Engineering Hainan Normal University Haikou Hainan 571158 China2 School of Physical Science and Technology Key Laboratory of Artificial Micro and Nano-Structures of the Ministry of EducationWuhan University Wuhan 430072 China

Correspondence should be addressed to Mengmei Pan panmengmei01163com

Received 26 February 2013 Accepted 16 March 2013

Academic Editor Shishang Guo

Copyright copy 2013 Mengmei Pan et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

How to improve the conversion efficiency and the stability of dye-sensitized solar cells (DSSCs) are two major problemsFurthermore reduction of the manufacturing cost of DSSCs and large-scale manufacture are also very important factors As a rawmaterial commercial P25 would be used for large-scale manufacture of TiO

2paste with simple preparation procedure However

there are several drawbacks for P25 such as the low surface area of P25 powder and the poor connectivity among particles in filmusing tradition P25 paste without modification In this paper we introduced a simple modified method by adding high surfacearea anatase TiO

2into pure P25 paste The photoelectric conversion performances of DSSCs based on these photo-electrodes were

tested The results show that the open-circuit voltage the fill factor and the energy conversion efficiency of the modified electrodewere increased It is found that the modified P25 films have fast electron transportation and a slow charge recombination Weconclude that through adding the anatase TiO

2nanoparticles to the P25 paste with high surface area it can not only improve the

particles connectivity among inside the films but also enhance the efficiency of DSSCs

1 Introduction

Titanium dioxide (TiO2) is a very important semiconductor

it has outstanding physicochemical properties such as heatresistance high refractive index and wide band gap TiO

2

nanocrystallites have been investigated widely in photocat-alytic degradation sensors dye-sensitized solar cells (DSSCs)[1 2] and so on With the shortage of fossil fuels and anincreasing demand for energy developing new types of cheapand environmentally friendly energy sources is becomingmore andmore important Dye-sensitized solar cells (DSSCs)as a new-generation solar cell was developed in the early1990s and it has attracted extensive attention attributed toits high conversion efficiency low production cost stableperformance and the simplicity of the process [3] DSSCswould be the most effective way of the utilization of solarenergy and one of the most promising technologies [4]

DSSCs operate similarly as photosynthesis which takesplace in leaves DSSCs consist of mesoporous TiO

2thin film

photoanode a nonaqueous electrolytic solution of the redox

couple IminusI3

minus and a platinized transparent conductive glassas a counter electrode When the DSSCs are illuminatedby sunlight the dyed molecules will be excited by lightabsorption Then the photon-generated electrons will beinjected into mesoporous TiO

2thin film Simultaneously

the oxidized dye molecules will accept electrons from Iminusin electrolyte to return to the ground state The electronsin the mesoporous TiO

2thin film will be collected by the

transparent conductive oxide electrodes and flow throughthe external circuit to the counter electrode To completethe reverse reaction of the redox couple a counter electrodemust be used to provide the electrons to I

3

minus Through theseprocesses solar energy is converted into electric energy [5]In order to realize future commercial production extensivestudies have been performed on each component of DSSCssuch as synthesis of TiO

2film types of dye sensitizer the

composition of electrolyte solution and counter electrodeThe mesoporous TiO

2thin film photoanode is one of

the main components of DSSCs and it plays a key role in

2 Journal of Nanomaterials

photovoltaic performances It is well known that a photoelec-trode with high efficiency should possess large surface areahigh light-harvesting efficiency rapid electron transport andlow electron recombination [3] It is well known that aftermodifications are always needed for TiO

2film because of the

insufficient connectivity between TiO2particles in the film

The poor connectivity would lead to low electron transportrate and high electron recombination hence reducing theconversion efficiency of DSSCs [6] Among many after-modifications TiCl

4posttreatment is widely used By this

modification an extra layer of TiO2will grow onto the

surface of the former TiO2film to enhance the connectivity

[7] Yu et al adopted a similar method by modifying theconventional porous TiO

2with a titanium organic sol [8]

On the other hand we need to design simple methodsto prepare TiO

2film for mass production TiO

2film via

hydrothermal method [9] achieved the highest efficiencywhile a several layers and steps are needed which limits itslarge-scalemanufacture In this paper we adopted a P25 pasteformass production and introduced a newmethod tomodifyit for enhancing the connectivity of particlesThe preparationof the P25 paste via bead mill is simple and just one layerand one step are needed to prepare TiO

2film which can be

easily used for the large-scale manufacture Furthermore themodification by adding high surface area anatase TiO

2into

pure P25 paste could cement the P25 nanoparticles togetherwhich could enhance the connectivity of particles to improvethe efficiency The performances of DSSCs using modifiedpaste were tested and compared to unmodified ones It isshowed that the open-circuit voltage the fill factor and theenergy conversion efficiency of the modified electrode wereincreased It is found that the modified P25 films have a rapidelectron transport rate and a slow charge recombination rate

2 Experimental Section

21Materials Thecommercial P25 powders (P25 20ndash30 nmsurface area 50m2g) [10]was purchased fromDegussa Ethy-lene glycol (EG) citric acid (CA) propylene carbonate (PC)anatase TiO

2 ethanol and nitric acid were all purchased

from Sinopharm Chemical Reagent Corporation (China)Distilled water (1825MΩ) was prepared in our laboratoryFluorine-doped SnO

2conductive glass (FTO sheet resis-

tance 10ndash15Ω sqminus1) was purchased from Asahi glass JapanIodine (I

2 998) was obtained from Beijing Yili chemicals

China Lithium iodide (LiI 99) 4-tertbutylpyridine (TBP)and guanidine thiocyanate (GNCS) were purchased fromAcros The Ru dye cis-di(thiocyanato)-bis(221015840-bipyridyl-441015840-dicarboxylate) ruthenium(II) (N719) was purchasedfrom Solaronix Switzerland [11] All the reagents used wereof analytical grade

22 Preparation of P25 Paste The unmodified P25 paste(Sample 1) was prepared by a bead-mill method 56 g of P25powder was ball-milled with 13mL of EG for 24 h and then126 g of CA was added to the above mixture for another 24 hthe processes were done at room temperature [10]

The first modified P25 paste (Sample 2) was preparedby adding 056 g of anatase TiO

2 504 g of P25 powder and

Bead mill 24 h

Sample 1

CACA CA

Bead mill 24 h Bead mill 24 h

Sample 2 Sample 3

Bead mill 24 h

Bead mill 24 h

504 g P25 + 504 g P25 + EG +56 g P25 + EG

Bead mill 24 h

anatase TiO2 EG + TiO2 sol

Figure 1 The steps for synthesizing anatase pastes

056 g of anatase TiO2(197m2g) powder were ball-milled

with 13mL of EG for 24 h then 126 g CA was added to themixture for another 24 h the processes were done at roomtemperature [10]

The second modified P25 paste (Sample 3) was pre-pared by adding TiO

2sol The TiO

2sol was prepared by

a hydrothermal method Typically 10mL of TTIP is mixedwith 21 g acetic acid and then using an ultrasonicatorultrasonicated for 15min The previous solutions were addeddrop-wise to 50mL of distilled water under vigorous stirringfor 1 hour Then 068mL of nitric acid was added to theprevious mixture solution and stirred for 6 h at 80∘C 10mLof transparent sol was obtained by evaporation of the waterThe preparation of the P25 paste modified with TiO

2sol

(Sample 3) was analogous to Sample 2 056 g of anatase TiO2

in Sample 2 was replaced by 2mL of TiO2sol in Sample 3The

flow diagrams for synthesizing these P25 pastes are shown inFigure 1

23 Preparation of Photoelectrodes and DSSCs The TiO2

pastes were coated onto FTO substrates by doctor-bladingrespectively and then they were sintered at 500∘C for 30minIn order to ensure the TiO

2mesoporous films with similar

thickness we pasted two layers of adhesive tapes on theedge of FTO the film with a thickness of about 143 120583m wasformed The mesoporous TiO

2photoelectrodes were pre-

heated at 120∘C for 30min after cooling down the electrodeswere washed with ethanol to remove the remaining smallglass fragments Afterwards theywere immersed in a 05mMethanolic N-719 solution for 24 h at room temperature toallow complete dye adsorption [11] After taking themout theredundant dyemolecules on the electrodes werewashed awayby ethanol for several times and then the electrodes weredried with a hair dryerThe dye-adsorbed TiO

2electrode was

assembled into a cell holder a drop of electrolyte solutionwas injected into the photoelectrode and a clamp was usedto press together the photoelectrode and a counter electrode(a platinum-sputtered F-SnO

2glass)The electrolyte solution

Journal of Nanomaterials 3

was composed of 005M LiI 003M I2 01M 1-propy-3-

methylimidazolium iodide 01M GNCS and 05M 4-tert-butylpyridine in a mixed solvent of acetonitrile and PC(volume ratio 11) A sandwich-type DSSC configuration wasfabricated [6]

3 Results and Discussion

31 Photovoltaic Performances of DSSCs The photocurrent-voltage characteristics of three DSSCs were measured bya CHI660C electrochemical Workstation (CH InstrumentsShanghai China) at room temperature Figure 2 shows thephotocurrent density and photovoltage characteristics ofthree DSSCs The resulting photovoltaic parameters derivedfrom the 119869-119881 are shown in Table 1

When we compare the photovoltaic performance param-eters of the TiO

2films modified by anatase TiO

2or TiO

2sol

to the original P25 film without modification as shown inFigure 2 we can observe that the open-circuit voltage (119881oc)and fill factor (FF) of Samples 2 3 have been increased andthe short-circuit photocurrent density (119869sc) slightly reducedbut the energy conversion efficiency increased The fill factor(FF) was calculated using (1) and the cellsrsquo overall energyconversion efficiency (120578) was estimated by (2) In (1) the119881max and 119869max are voltage and current density for maximumpower output respectively In (2) the 119875in is the intensity ofthe incident light (829mWcm2) [8]

FF =119881max119869max119881oc119869sc (1)

120578 =119881oc119869scFF119875in (2)

The charge recombination can be estimated by themagni-tude and onset of dark current Recombination reaction hap-pens between electron at conduction band of semiconductorand redox couple in electrolyte which is described by thefollowing [9]

2119890minus

CB + I3minus997888rarr 3Iminus (3)

Figure 2(b) shows the dark current-voltage characteris-tics of the photoanodes with and without modification Thedark current measurement suggested that the modified pho-toanodes had a slower photoelectrons recombination rate Itis noteworthy to see that the P25 photoelectrode modifiedwith TiO

2sol TiO

2produces the lowest dark current while

the P25 photoelectrode without modification produces thehighest dark current at the same potential about 06V Theseobservations reflect a higher recombination at the P25 pho-toelectrode (Sample 1) than the P25 photoelectrode modifiedwith anatase TiO

2(Sample 2) and TiO

2sol (Sample 3) which

is supported by EIS measurements in Section 32

32 EIS and OCVD Analyses In order to confirm the specu-lation thatmodification is beneficial to retard electron recom-bination and facilitate electron transport electrochemicalimpedance spectroscopy (EIS) measurements were carriedout to investigate the kinetics of the electrochemical processes

Table 1 119869-119881 Parameters for Sample 1 2 and 3

DSSCs 119881ocmV 119869scmA cm2 FF 120578Sample 1 727 900 064 532Sample 2 737 866 071 550Sample 3 749 872 070 553

Table 2 Parameters obtained by fitting the impedance spectra ofDSSCs using the equivalent circuit in Figure 3

DSSCs 1198771Ω 119877

2Ω 119877

3Ω 119865maxHz 120591

119890ms

Sample 1 1324 7902 2047 5486 00290Sample 2 1884 5109 1911 4542 00351Sample 3 1636 9709 1893 4542 00351

of DSSCs The impedance spectra of DSSCs based on thethree films (Sample 1 Sample 2 and Sample 3) under one-sun illumination were measured at the frequency rangeof 10minus1-105 Hz at the open circuit respectively Figure 3(a)shows the Nyquist plots which exhibit two semicirclesincluding a large semicircle at low frequencies and a small oneat high frequencies the plots were fitted with an equivalentcircuit [12] (shown in the inset of Figure 3(a))The equivalentcircuit consisted of119877

1which is ascribed to the sheet resistance

of FTO and contacting resistance 1198772which is ascribed to

the contact resistance between the FTO and TiO2film and

the charge transfer resistance at the interfaces of the redoxelectrolytePt counter electrode and 119877

3which is ascribed to

the charge transport resistance of the accumulationtransportof the injected electrons within TiO

2film and the charge

transport resistance at the TiO2redox electrolyte interfaces

CPE1 and CPE2 are constant phase elements of the capac-itance corresponding to 119877

2and 119877

3 respectively [4] As

shown in Table 2 the paste modified with TiO2sol exhibits

the lowest values of 1198773among the three types of DSSCs

which implies themost efficient charge-transfer process at theinterface of TiO

2electrolyte interfaces and across TiO

2film

By adding small particles into the paste it could cement theTiO2nanoparticles together so the electron pathways would

be widened [8] Consequently the overall efficiency would beincreased by the enhanced electron transfer efficiency

The Bode phase plots of EIS spectra as shown inFigure 3(b) display the frequency peaks of the charge transferprocess at different interfaces of three different DSSCsThe characteristic low frequency peak (119891max) is located at5486Hz for Sample 1 4542Hz for Sample 2 and Sample 3Table 2 shows the electron lifetime for recombination (120591

119890)

of DSSC The electron lifetime in DSSCs is determined bythe characteristic frequency peak in the low frequency (119891max)according to the following [13]

120591119890=1

2120587119891max (4)

We can notice that the DSSCsrsquo electron lifetimes using themodified pastes were longer than that without modificationwhich implies that the modified pastes could improve theelectron lifetime The longest electron lifetime is due to


10

8

6

4

2

0

minus2

minus4

0 02 04 06 08Voltage (V)

Sample 1Sample 2Sample 3

Curr

ent d

ensit

y (m

A cm

minus2)

(a)


0

minus2

minus4

minus6

Voltage (V)0 02 04 06 08

Curr

ent d

ensit

y (m

A cm

minus2)

(b)

Figure 2 Current density-voltage characteristics of DSSCs based on the P25 photoanode (Sample 1) the photoanodes modified by anataseTiO2(Sample 2) and TiO

2sol (Sample 3) measured under simulated sunlight (a) and under dark (b)

12

10

8

6

4

2

0

CPE1 CPE2

15 20 25 30 35 40 45


minus119885998400998400

(Ω)

119885998400 (Ω)

1198771 1198772 1198773

(a)

120591(s

)

18

16

14

12

10

8

6

4

2

Time (s)01 1 10 100 1000 10000 100000


(b)

Figure 3 EIS spectra of DSSCs based on the P25 photoanode the photoanodes modified by anatase TiO2and TiO

2sol (a) Nyquist plots

(b) Bode phase plots

the lowest recombination between electrons injected from theexcited dye and I

3

minusThe open-circuit voltage decay (OCVD) technique was

employed for investigating the electron lifetime (120591119890) which

is conducted by turning off the illumination on DSSC ina steady state and monitoring the subsequent decay of119881oc The electron lifetime was calculated by the followingequation where 119896

119861is the Boltzmann constant 119879 is the

absolute temperature and 119890 is the positive elementary charge[14 15]

120591119890=119896119861119879

119890(119889119881oc119889119905)

minus1

(5)

Figure 4(a) shows OVCD spectra of DSSCs based on theP25 photoanode the photoanodes modified by anatase TiO

2

and TiO2sol respectively Figure 4(b) shows the electron


08

07

06

05

04

03

02

01

0

Ope

n-ci

rcui

t vol

tage

(V)

0 5 10 15 20Time (s)


(a)

119881oc (V)

10

1

01

120591(s

)

0 01 02 03 04 05 06 07 08


(b)

Figure 4 (a) OCVD spectra of DSSCs based on the P25 photoanode the photoanodes modified by anatase TiO2and TiO

2sol respectively

(b) The electron lifetime spectra of these DSSCs

lifetime spectra of these samples As shown in Figure 4(b)we could note that the variation trend of the electron lifetimemeasured by OCVD is the same as the EIS results Theelectron having longer electron lifetime and faster transferrate would be a result of additional electron pathways in theTiO2film [16] As a result the TiO

2pastesmodifiedwith high

surface anatase TiO2could improve the performance of the

TiO2films in DSSCs

4 Conclusion

In summary we have successfully fabricated three kindsof modified P25 pastes and investigated them in DSSCsphotoanodes We employed high surface area anatase TiO

2

to improve the connectivity among the TiO2particles The

photoelectric measurement results showed that the modifiedcells have low charge transport resistance and long electronlifetime it is assigned that the rapid electrons transport ratedelays the process of their recombination The photoelectricmeasurement results showed that open-circuit voltage (119881oc)the fill factor (FF) and the energy conversion efficiency allhave remarkably increased We conclude that through theaddition of extra anatase TiO

2in P25 paste the electron

pathways inside TiO2film would be enlarged which would

result in high photoelectric parameters In brief we introducea simple and effective strategy which provides a goodway to improve the overall energy conversion efficiency ofDSSCs

Conflict of Interests

The authors do not have any conflict of interests in theirsubmitted paper

Acknowledgment

Theauthors acknowledge the financial support by theNaturalScience Foundation of Hainan Province of China (511116)

References

[1] E C Muniz M S Goes J J Silva et al ldquoSynthesis and sharac-erization of mesoporous TiO

2nanostructured films prepared

by a modified sol-gel method for application in dye solar cellsrdquoCeramics International vol 37 no 4 pp 1017ndash1024 2011

[2] A Luque and A Mart ldquoIncreasing the efficiency of ideal solarcells by photon induced transitions at intermediate levelsrdquoPhysical Review Letters vol 78 no 2 pp 5014ndash5017 1997

[3] G Dai L Zhao S Wang et al ldquoDouble-layer composite filmbased on sponge-like TiO

2and P25 as photoelectrode for

enhanced efficiency in dye-sensitized solar cellsrdquo Journal ofAlloys and Compounds vol 539 no 10 pp 264ndash270 2012

[4] J Navas C Fernandez-Lorenzo T Aguilar R Alcantara andJ Martın-Calleja ldquoImproving open-circuit voltage in DSSCsusing Cu-doped TiO

2as a semiconductorrdquo Physica Status Solidi

A vol 209 no 2 pp 378ndash385 2012[5] P M Sommeling B C OrsquoRegan R R Haswell et al ldquoInfluence

of a TiCl4post-treatment on nanocrystalline TiO

2films in dye-

sensitized solar cellsrdquo Journal of Physical Chemistry B vol 110no 39 pp 19191ndash19197 2006

[6] C H Zhou H Hu Y Yang et al ldquoEffect of thickness onstructural electrical and electrochemical properties of plat-inumtitanium bilayer counterelectroderdquo Journal of AppliedPhysics vol 104 no 8 Article ID 034910 6 pages 2008

[7] S S Kim JH Yum andY E Sung ldquoImproved performance of adye-sensitized solar cell using a TiO

2ZnOEosin Y electroderdquo

Solar Energy Materials and Solar Cells vol 79 no 4 pp 495ndash505 2003


[8] H Yu S Zhang H Zhao B Xue P Liu and G WillldquoHigh-performance TiO

2photoanode with an efficient electron

transport network for dye-sensitized solar cellsrdquo Journal ofPhysical Chemistry C vol 113 no 36 pp 16277ndash16282 2009

[9] C H Zhou S Xu Y Yang et al ldquoTitanium dioxide solssynthesized by hydrothermal methods using tetrabutyl titanateas starting material and the application in dye sensitized solarcellsrdquo Electrochimica Acta vol 56 no 11 pp 4308ndash4314 2011

[10] C C Tsai and H Teng ldquoChromium-doped titanium dioxidethin-film photoanodes in visible-light-induced water cleavagerdquoApplied Surface Science vol 254 no 15 pp 4912ndash4918 2008

[11] N Huang Y Liu T Peng et al ldquoSynergistic effects of ZnOcompact layer and TiCl

4post-treatment for dye-sensitized solar

cellsrdquo Journal of Power Sources vol 204 pp 257ndash264 2012[12] Y-Z Zheng X Tao L-X Wang et al ldquoNovel ZnO-based

film with double light-scattering layers as photoelectrodes forenhanced efficiency in dye-sensitized solar cellsrdquo Chemistry ofMaterials vol 22 no 9 pp 928ndash934 2010

[13] N G Park J van de Lagemaat and A J Frank ldquoComparisonof dye-sensitized rutile- and anatase-based TiO

2solar cellsrdquo

Journal of Physical Chemistry B vol 104 no 38 pp 8989ndash89942000

[14] A Zaban M Greenshtein and J Bisquert ldquoDetermination ofthe electron lifetime in nanocrystalline dye solar cells by open-circuit voltage decay measurementsrdquo ChemPhysChem vol 4no 8 pp 859ndash864 2003

[15] J Bisquert A Zaban M Greenshtein and I Mora-SeroldquoDetermination of rate constants for charge transfer and thedistribution of semiconductor and electrolyte electronic energylevels in dye-sensitized solar cells by open-circuit photovoltagedecay methodrdquo Journal of the American Chemical Society vol126 no 41 pp 13550ndash13559 2004

[16] Y-Z Zheng X Tao L-X Wang et al ldquoNovel ZnO-basedfilm with double light-scattering layers as photoelectrodes forenhanced efficiency in dye-sensitized solar cellsrdquo Chemistry ofMaterials vol 22 no 9 pp 928ndash934 2010

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MaterialsJournal of


Nano

materials


Journal ofNanomaterials


photovoltaic performances It is well known that a photoelec-trode with high efficiency should possess large surface areahigh light-harvesting efficiency rapid electron transport andlow electron recombination [3] It is well known that aftermodifications are always needed for TiO

2film because of the

insufficient connectivity between TiO2particles in the film

The poor connectivity would lead to low electron transportrate and high electron recombination hence reducing theconversion efficiency of DSSCs [6] Among many after-modifications TiCl

4posttreatment is widely used By this

modification an extra layer of TiO2will grow onto the

surface of the former TiO2film to enhance the connectivity

[7] Yu et al adopted a similar method by modifying theconventional porous TiO

2with a titanium organic sol [8]

On the other hand we need to design simple methodsto prepare TiO

2film for mass production TiO

2film via

hydrothermal method [9] achieved the highest efficiencywhile a several layers and steps are needed which limits itslarge-scalemanufacture In this paper we adopted a P25 pasteformass production and introduced a newmethod tomodifyit for enhancing the connectivity of particlesThe preparationof the P25 paste via bead mill is simple and just one layerand one step are needed to prepare TiO

2film which can be

easily used for the large-scale manufacture Furthermore themodification by adding high surface area anatase TiO

2into

pure P25 paste could cement the P25 nanoparticles togetherwhich could enhance the connectivity of particles to improvethe efficiency The performances of DSSCs using modifiedpaste were tested and compared to unmodified ones It isshowed that the open-circuit voltage the fill factor and theenergy conversion efficiency of the modified electrode wereincreased It is found that the modified P25 films have a rapidelectron transport rate and a slow charge recombination rate

2 Experimental Section

21Materials Thecommercial P25 powders (P25 20ndash30 nmsurface area 50m2g) [10]was purchased fromDegussa Ethy-lene glycol (EG) citric acid (CA) propylene carbonate (PC)anatase TiO

2 ethanol and nitric acid were all purchased

from Sinopharm Chemical Reagent Corporation (China)Distilled water (1825MΩ) was prepared in our laboratoryFluorine-doped SnO

2conductive glass (FTO sheet resis-

tance 10ndash15Ω sqminus1) was purchased from Asahi glass JapanIodine (I

2 998) was obtained from Beijing Yili chemicals

China Lithium iodide (LiI 99) 4-tertbutylpyridine (TBP)and guanidine thiocyanate (GNCS) were purchased fromAcros The Ru dye cis-di(thiocyanato)-bis(221015840-bipyridyl-441015840-dicarboxylate) ruthenium(II) (N719) was purchasedfrom Solaronix Switzerland [11] All the reagents used wereof analytical grade

22 Preparation of P25 Paste The unmodified P25 paste(Sample 1) was prepared by a bead-mill method 56 g of P25powder was ball-milled with 13mL of EG for 24 h and then126 g of CA was added to the above mixture for another 24 hthe processes were done at room temperature [10]

The first modified P25 paste (Sample 2) was preparedby adding 056 g of anatase TiO

2 504 g of P25 powder and

Bead mill 24 h

Sample 1

CACA CA

Bead mill 24 h Bead mill 24 h

Sample 2 Sample 3

Bead mill 24 h

Bead mill 24 h

504 g P25 + 504 g P25 + EG +56 g P25 + EG

Bead mill 24 h

anatase TiO2 EG + TiO2 sol

Figure 1 The steps for synthesizing anatase pastes

056 g of anatase TiO2(197m2g) powder were ball-milled

with 13mL of EG for 24 h then 126 g CA was added to themixture for another 24 h the processes were done at roomtemperature [10]

The second modified P25 paste (Sample 3) was pre-pared by adding TiO

2sol The TiO

2sol was prepared by

a hydrothermal method Typically 10mL of TTIP is mixedwith 21 g acetic acid and then using an ultrasonicatorultrasonicated for 15min The previous solutions were addeddrop-wise to 50mL of distilled water under vigorous stirringfor 1 hour Then 068mL of nitric acid was added to theprevious mixture solution and stirred for 6 h at 80∘C 10mLof transparent sol was obtained by evaporation of the waterThe preparation of the P25 paste modified with TiO

2sol

(Sample 3) was analogous to Sample 2 056 g of anatase TiO2

in Sample 2 was replaced by 2mL of TiO2sol in Sample 3The

flow diagrams for synthesizing these P25 pastes are shown inFigure 1

23 Preparation of Photoelectrodes and DSSCs The TiO2

pastes were coated onto FTO substrates by doctor-bladingrespectively and then they were sintered at 500∘C for 30minIn order to ensure the TiO

2mesoporous films with similar

thickness we pasted two layers of adhesive tapes on theedge of FTO the film with a thickness of about 143 120583m wasformed The mesoporous TiO

2photoelectrodes were pre-

heated at 120∘C for 30min after cooling down the electrodeswere washed with ethanol to remove the remaining smallglass fragments Afterwards theywere immersed in a 05mMethanolic N-719 solution for 24 h at room temperature toallow complete dye adsorption [11] After taking themout theredundant dyemolecules on the electrodes werewashed awayby ethanol for several times and then the electrodes weredried with a hair dryerThe dye-adsorbed TiO

2electrode was

assembled into a cell holder a drop of electrolyte solutionwas injected into the photoelectrode and a clamp was usedto press together the photoelectrode and a counter electrode(a platinum-sputtered F-SnO

2glass)The electrolyte solution








2or TiO

2sol


FF =119881max119869max119881oc119869sc (1)

120578 =119881oc119869scFF119875in (2)


2119890minus



2sol TiO



2(Sample 2) and TiO







DSSCs 1198771Ω 119877

2Ω 119877

3Ω 119865maxHz 120591

119890ms












2and 119877






2film




119890)


120591119890=1

2120587119891max (4)



10

8

6

4

2

0

minus2

minus4

0 02 04 06 08Voltage (V)


Curr

ent d

ensit

y (m

A cm

minus2)

(a)


0

minus2

minus4

minus6

Voltage (V)0 02 04 06 08

Curr

ent d

ensit

y (m

A cm

minus2)

(b)



12

10

8

6

4

2

0

CPE1 CPE2

15 20 25 30 35 40 45


minus119885998400998400

(Ω)

119885998400 (Ω)

1198771 1198772 1198773

(a)

120591(s

)

18

16

14

12

10

8

6

4

2

Time (s)01 1 10 100 1000 10000 100000


(b)





3






120591119890=119896119861119879

119890(119889119881oc119889119905)

minus1

(5)


2



08

07

06

05

04

03

02

01

0

Ope

n-ci

rcui

t vol

tage

(V)

0 5 10 15 20Time (s)


(a)

119881oc (V)

10

1

01

120591(s

)

0 01 02 03 04 05 06 07 08


(b)


2sol respectively





TiO2films in DSSCs

4 Conclusion


2








Acknowledgment


References












2films in dye-

















2solar cellsrdquo












CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










2or TiO

2sol


FF =119881max119869max119881oc119869sc (1)

120578 =119881oc119869scFF119875in (2)


2119890minus



2sol TiO



2(Sample 2) and TiO







DSSCs 1198771Ω 119877

2Ω 119877

3Ω 119865maxHz 120591

119890ms












2and 119877






2film




119890)


120591119890=1

2120587119891max (4)



10

8

6

4

2

0

minus2

minus4

0 02 04 06 08Voltage (V)


Curr

ent d

ensit

y (m

A cm

minus2)

(a)


0

minus2

minus4

minus6

Voltage (V)0 02 04 06 08

Curr

ent d

ensit

y (m

A cm

minus2)

(b)



12

10

8

6

4

2

0

CPE1 CPE2

15 20 25 30 35 40 45


minus119885998400998400

(Ω)

119885998400 (Ω)

1198771 1198772 1198773

(a)

120591(s

)

18

16

14

12

10

8

6

4

2

Time (s)01 1 10 100 1000 10000 100000


(b)





3






120591119890=119896119861119879

119890(119889119881oc119889119905)

minus1

(5)


2



08

07

06

05

04

03

02

01

0

Ope

n-ci

rcui

t vol

tage

(V)

0 5 10 15 20Time (s)


(a)

119881oc (V)

10

1

01

120591(s

)

0 01 02 03 04 05 06 07 08


(b)


2sol respectively





TiO2films in DSSCs

4 Conclusion


2








Acknowledgment


References












2films in dye-

















2solar cellsrdquo












CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




10

8

6

4

2

0

minus2

minus4

0 02 04 06 08Voltage (V)


Curr

ent d

ensit

y (m

A cm

minus2)

(a)


0

minus2

minus4

minus6

Voltage (V)0 02 04 06 08

Curr

ent d

ensit

y (m

A cm

minus2)

(b)



12

10

8

6

4

2

0

CPE1 CPE2

15 20 25 30 35 40 45


minus119885998400998400

(Ω)

119885998400 (Ω)

1198771 1198772 1198773

(a)

120591(s

)

18

16

14

12

10

8

6

4

2

Time (s)01 1 10 100 1000 10000 100000


(b)





3






120591119890=119896119861119879

119890(119889119881oc119889119905)

minus1

(5)


2



08

07

06

05

04

03

02

01

0

Ope

n-ci

rcui

t vol

tage

(V)

0 5 10 15 20Time (s)


(a)

119881oc (V)

10

1

01

120591(s

)

0 01 02 03 04 05 06 07 08


(b)


2sol respectively





TiO2films in DSSCs

4 Conclusion


2








Acknowledgment


References












2films in dye-

















2solar cellsrdquo












CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




08

07

06

05

04

03

02

01

0

Ope

n-ci

rcui

t vol

tage

(V)

0 5 10 15 20Time (s)


(a)

119881oc (V)

10

1

01

120591(s

)

0 01 02 03 04 05 06 07 08


(b)


2sol respectively





TiO2films in DSSCs

4 Conclusion


2








Acknowledgment


References












2films in dye-

















2solar cellsrdquo












CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials














2solar cellsrdquo












CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article enhanced efficiency of dye-sensitized

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