electrochim acta 75, 2012

7/23/2019 Electrochim Acta 75, 2012

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Post-print of: Electrochimica Acta Volume 75, 30 July 2012, Paes 13!"1#7

http:$$%&'%oi'or$10'101($)'electacta'2012'0#'0*7

Efect o nanostructured electrode architecture and semiconductordeposition strategy on the photovoltaic perormance o quantum

dot sensitized solar cells

+ahmou% ama%pour a, , i&to .im/ne a, Palo P' oi& a, in hen c,

%, +auricio E' al4o e, ima 6aha4inia , f, Aam ra)i a% , f, 6aro

6oyo%a c, 8ern9n +ue e, 49n +ora-er; a

a .rup %e ptoelectr?nics, o& 11155-*(3!, 6ehran, ran

c , Japan cience an% 6echnoloy Aency CJ6D, #-1-* 8oncho

aFauchi, aitama 332-0012, Japan

e nstituto %e iencia %e +ateriales %e e4illa, -@, A4eni%a Am/rico

Vespucio #!, #10!2 e4illa, pain

f o& 11155-

!1(1, 6ehran, ran

Abstract

8ere Fe analye the eGect of tFo rele4ant aspects relate% to cell

preparation on Huantum %ot sensitie% solar cells C2 nanostructure% electro%e an% the roFth metho% of

Huantum %ots C2 %epen%s on the


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metho%' 8iher Voc 4alues are systematically otaine% for 6i>2

morpholoies Fith %ecreasin surface area an% for cells usin < roFth

metho%' 6his is systematically correlate% to a hiher recomination

resistance of < sensitie% electro%es' Electron in)ection inetics from 2 also %epen%s on oth the 6i>2 structure an% the


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oth the architecture of the Fi%e an%ap o&i%e semicon%uctor 6i>2 an%

the liht asorin semicon%uctor %eposition stratey on the photo4oltaic

performance of


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N3#O an% successi4e ionic layer a%sorption an% reaction CABD N12O' oth

metho%s are ase% on loF cost solution processes, i%eal for up-scalin an%

farication of cost-eGecti4e photo4oltaic %e4ices' Ie ha4e carrie% out a

systematic stu%y comprisin structural, optical, photophysical an%

photoelectrochemical characteriation in or%er to correlate the material

properties of the photoano%es Fith the functional performance of themanufacture% D' 6he three

nanoparticulate% structures CP20, P250 an% P20"#50D Fere otaine% fromcommercial pastes from C6i>2 particle sie 250 nmD an% C6i>2 particle sie 20"#50

nmD, respecti4ely' 6he rst paste pro%uces electro%es Fith hih eGecti4e

surface area, Fhile the other tFo are commonly employe% as liht

scatterin layers in materialD Fere %octor-

la%e% on transparent con%uctin Tuorine %ope% tin o&i%e C=6>D lass

sustrates Csheet resistance U10 $WD' 6he resultin photoelectro%es Fere

sintere% at #50 S, to otain oo% mechanical an% electrical contact at the

interfaces 6i>2$6i>2 an% 6i>2$sustrate' efore %eposition of the %iGerent

6i>2 structures, the =6> sustrates Fere coate% y a compact layer of 6i>2

%eposite% y spray pyrolysis CU100 nm thicD' 6hese electro%es Fere

calcinate% at #50 S for 30 min' =or samples > an% =, it has een %etecte% a

loF mechanical staility an% poor a%hesion Fith the sustrate'

#


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.. Electrode sensitization

6he %iGerent 6i>2 nanostructure% electro%es Fere sensitie% y %$%e

2 Forin electro%e into

the metal precursors an% suseHuently into the sul%e solutions' After each

ath, the photoano%e is thorouhly rinse% y immersion in the

correspon%in sol4ent to remo4e the chemical resi%uals from the surface

an% suseHuently %rie% in air' 6he %e %eposition after % coatin Fas

performe% y tFo metho%s AB an% 3D solution Fas prepare% y reTu&in elemental e

an% a2>3 in +illi- Fater at *0 S for ( h Fith 2 Tu&' 6he chemical ath

solution Fas prepare% y mi&in *0 m+ of %># an% *0 m+ of a2e>3

solution Fith 120 m+ of nitriloacetic aci%' 6he sensitie% 6i>2 electro%es

Fere immerse% in the chemical ath solution at 10 S for 12 h' 6hen, the

electro%es Fere Fashe% Fith +illi- Fater an% %rie% Fith 2 un' t is Fell

noFn that a see% layer of % sinicantly enhances the roFth rate of

%e, pro%ucin an increase of the liht asorption for the same >D2 an% 0'1 + a2 solutions for 1 min$%ip, rinsin Fith +illi-

ultrapure Fater etFeen %ips N#1O' At least tFo cells Fith the same

con%itions C6i>2 nanostructure an% < %eposition mo%eD ha4e een

prepare% an% analye%'

.%. &'"( preparation

6he solar cells Fere prepare% y san%Fichin a u2 counter electro%e an%

a 8 solution in +illi- ultrapure

5


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Fater N13O an% N1#O' 6he u2 counter electro%es Fere prepare% y

immersin a rass foil in 8l solution at 70 S for 5 min an% suseHuently

%ippin it into polysul%e solution for 10 min, resultin in a porous u2

electro%e' 6he eometric area of the cells Fas 0'2* cm2'

.). *hotoanode and solar cell characterization

.as a%sorption measurements, E6, Fere performe% on a +icromeritics

AAP 2020 surface area an% porosity analyer Fith the AAP 2020 V3'0# E

softFare' 6hree measurements Fere carrie% out for each specimen in or%er

to assess the repro%uciility of the results' +icrostructural e&amination of

the sensitie% photoano%es Fas carrie% out y a J+-7000= JE> =E.-E+

system C6oyo, JapanD' 6ransmission electron microscopy Fas carrie% out y

usin a hih resolution 6E+ C8B6E+D =iel% Emission .un JE+-2100 electron

microscope CJE>D operate% at 200 V' 6E+ samples Fere prepare% y

rain oG the mesoporous sensitie% photoano%es from the =6> coate%

lass' 6he poF%er specimens Fere sonicate% in asolute ethanol for 5 min,

an% a feF %rops of the resultin suspension Fere %eposite% onto a holey-

caron lm supporte% on a copper ri%, Fhich Fas suseHuently %rie%'

6he optical asorption spectra of the photoano%es Fere recor%e% in the

rane of 300"*00 nm y a ary 500 @V-V Varian spectrometer, no

interatin sphere has een employe% in the measurement' urrent"

potential CJ"VD cur4es, impe%ance spectroscopy CD measurement, applie%

ias 4oltae %ecay CAVriel nstruments' mpe%ance spectroscopy measurements Fere

carrie% out in %ar con%itions applyin a 20 mV A sinal Fith the freHuency

ranin etFeen #00 8 an% 0'1 8 at %iGerent forFar% iases' @ltrafast

carrier %ynamics ha4e een e4aluate% y the lens-free hetero%yne %etection

transient ratin C=-8PAD Ca 6>AP from uantroni&D to

enerate liht pulses Fith a Fa4elenth tunale from 2!0 nm to 3 ZmL use%

as a pump liht in the 6. measurement' n this stu%y, the pump pulse

Fa4elenth Fas 520 nm an% the proe pulse Fa4elenth Fas 775 nm' ince

most reliale results are otaine% Forin in transmission conuration,only P20 an% = specimens Fere teste%'

(


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%. +esults and discussion

%.1. "tructural characterization

6he relationship etFeen structural features an% functional performance of

the %e4ices pro4i%es a poFerful tool oth to un%erstan% the mechanisms of

the rele4ant processes tain place %urin %e4ice operation as Fell as to

optimie the %esin of the %iGerent components lea%in to optimum

performance N10O' =i' 1 shoFs the top 4ieF of the %iGerent 6i>2 structures

stu%ie%' 6he cross sectional 4ieFs are inclu%e% in the upplementary

nformation as =i' 1' =rom these microraphs, it is clear the %iGerent

electro%e morpholoy an% the %iGerent sie %istriution of the

nanoparticulate% structures' n a%%ition, E6 measurements Fere use% for

the %etermination of the pore sie' 6he P20 material is characterie% y a

narroF sie %istriution aroun% 20 nm Csee =i' 2D, an% it is use% as the

typical structure for transparent 6i>2 electro%es' 6he other tFo

nanoparticulate% systems CP20"#50 an% P250D are use% as scatterin layers

in ' @pon sensitiation y AB

or < metho%s, the structure of the 6i>2 photoelectro%es in noF

conformally coate% Fith a thin lm of %$%e Cthicness aroun% 5 nmD'

6hese structures Fere measure% y 6E+ an% are shoFn in the

upplementary +aterial in =i' 2' =rom these 6E+ microraphs, no

sinicant morpholoical chanes in the


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>ne of the ey functional properties of the photoelectro%es is the liht

har4estin capaility' onseHuently, the optical asorance of the sensitie%

electro%es is shoFn in =i' 3' 6here is a oo% correlation etFeen the

asorance an% the surface area in%epen%ently of the sensitiation metho%

CAB or 2

eGecti4e surface area' on4ersely, the correspon%ence of the measure%PE C=i' 3D Fith the surface area of the electro%es is %epen%ent on the

sensitiation metho%' Ihen AB is employe%, the PE increases

monotonically Fith the surface area of the electro%es Ci'e' optical

asoranceD, Fhile Fhen < is use%, this tren% is not folloFe% for the

hihest surface area structure Cmaterial 6D' 6he ma&imum PE 4alues

otaine% in the present stu%y are aout (0"70M' 6he use of 6i>2 layers Fith

%iGerent structures in the same electro%e in or%er to impro4e the liht

scatterin enhances the PE results otaine% in this For N1!O, N20O, N23O

an% N3(O, ut are not in the scope of the present stu%y' n this stu%y Fe are

intereste% in the eGect of each particular structure on the 2 structures rane%

y acti4e surface area C> ] = ] P250 ] P20"#50 ] = R P20 ] P20D an% for

oth


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interme%iate surface area CP20"#50 structureD, an% %ecreasin for the

samples Fith hihest surface area' 6he %escrie% tren%s ha4e the folloFin

implications: the solar cell parameters stronly %epen% on oth the

architecture of the nanostructure% electro%e an% the < roFth metho%'

=ocusin on the eGect on Voc, Fe systematic oser4e% hiher Voc 4alues for

< samples, see =i' (' ote, %espite the poor a%hesion of the stu%ie% >an% = electro%es Voc is also hiher for < cells in this situation compare%

to AB samples' >pen structures Ci'e' loFer eGecti4e surface areaD also

e&hiit hiher Voc 4alues' 6he AB metho% is more a%eHuate for structures

Fith hih surface area' on4ersely, the < metho% pro%uces etter

performin %e4ices for more opene% structures, see 6ale 2' n the 2 con%uction an%'>n the other han%, a shift in Z can e oser4e% %epen%in on the 6i>2

structure' amples prepare% Fith scatterin pastes e&hiit an upFar%s

%isplacement of the con%uction an%, contriutin to the hiher Voc

otaine% for P20"#50 an% P250 samples in comparison Fith P20 sample, see

6ale 2, note that comparin samples usin the same %eposition metho%,

AB or


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CloFer recomination rateD N#*O compare% to AB samples' 6he > structure

is an e&ception, ut the results otaine% Fith this structure are less

repro%ucile %ue to mechanical a%hesion prolems, lea%in to %iKculties for

the %irect comparison etFeen %iGerent samples' 6his tren% e&plains the

hiher Voc %etecte% in < cells' >n the other han%, it has een shoFn that

the 2 morpholoies an% 2$%e nanocomposite

structures can e tte% to a %oule e&ponential %ecay N32O, N3!O an% N50O:

Y A1eYt$1RA2eYt$2

Fhere A1 an% A2 are pree&ponential factors an% _1 Cfast componentD

reTects the electron in)ection from 2

surface an% the contriution of hole %ynamics Cpro4i%e% that the ratio A1$A2

is close to 0'3D, see =i' !CaD N32O' >n the other han%, _2 CsloF componentD

inclu%es the contriution to the electron in)ection from 2, see =i' !CaD N32O' 6he results of the ttins are

shoFn in 6ale 3 for P20 an% = structures Fith %e 2:=D in the case of

= sample' t has een shoFn that the < in)ection from %e 2

is faster than the in)ection into 6i>2N51O' omparin oth


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a stron inTuence on oth the electron in)ection an% the recomination

process'

). (onclusions

Ie %emonstrate% the ey role of the 6i>2 structure an% the 2 is %iGerent for oth 2 morpholoies an% for the < metho%' 6his is

systematically correlate% to an upFar%s shift in the 6i>2 con%uction an% of

scatterin pastes Fith rear% to transparent paste an% to the hiher

recomination resistance CloFer recomination rateD oser4e% for 2 structures' CaD =,

CD P20"#50, CcD P250, C%D P20, CeD = R P20 an% CfD >' 6he scale ar is 500

nm for all microraphs'

=iure 2' ie %istriution e&tracte% from E6 measurements for the

%iGerent structures teste%'

=iure 3' >ptical asorance of the sensitie% electro%es an% PE of the

respecti4e manufacture% solar cells'

=iure #' J"V cur4es of the %iGerent solar cells'

=iure 5' Photo4oltaic parameters for the %iGerent 6i>2 morpholoies

rane% y surface area C> ] = ] P250 ] P20"#50 ] = R P20 ] P20D for oth2 structures an% for oth


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6ale 1

Table 1. BET surface area, porosity and total area of the electrodes with the

different TiO2structures (geometrical area of the electrodes is 0.2 cm

2

!.

#i$morphology E# /m0g *orosity #otal surace /cm

= *2'*# 0'!0 2(*a

P20"#50 27'33 0'2! 250

P250 10'15 0'31 !2

P20 73'*2 0'#0 (75

a urface area consi%erin the 2"3 nm porosity, see =i' 2, note that

the surface a4ailale for < %eposition is sensily loFer as the

electrochim acta 75, 2012

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