(2) quantum dot solar cells

7/24/2019 (2) Quantum Dot Solar Cells

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uantum ot o aruan um o o ar

Cells.Cells.

Tuning PhotoresponseTuning Photoresponsethroughthrough

Size and Shape ControlSize and Shape Controlof CdSeof CdSe--TiO2TiO2

ArchitectureArchitectureKiarash KiantajKiarash KiantajC2!"#Spring 2$$%C2!"#Spring 2$$%


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IntroductionIntroduction

Sensitization of mesoscopic Tio2Sensitization of mesoscopic Tio2

&ith d'es ())* e+icienc',&ith d'es ())* e+icienc',

Short -and gap semiconductors toShort -and gap semiconductors totransfer electrons to large -and gaptransfer electrons to large -and gap

semiconductorssemiconductors

Sensitizers/ CdS0 P-S0 1i2S! CdSe0nP (short gap,

TiO2 0 SnO2 ( large gap,


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Short band gap semi-Short band gap semi-

conductorsconductors 3ar4esting 4isi-le light energ'.3ar4esting 4isi-le light energ'.

lectron injection under 4isi-le lightlectron injection under 4isi-le light

5ast charge recom-ination5ast charge recom-ination lo&lo&e+icienc'e+icienc'


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Semiconductor QuantumSemiconductor Quantum

dotsdots6isi-le light har4esting assem-lies6isi-le light har4esting assem-lies

Size 7uantizationSize 7uantization

Tune 4isi-le responseTune 4isi-le response6ar' -and energies6ar' -and energies

Open up &a's utilize hot electronsOpen up &a's utilize hot electrons

and multiple carriers &ith singleand multiple carriers &ith singlephoton.photon.


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Quantized CdSe Particles andTheir Deposition on TiO2

Particulate Films and Nanotubes

8andom 4ersus Directed lectron Transport throughSupport Architectures0 (a, TiO2 Particle and (-, TiO2 9anotu-e5ilms :odi;ed &ith CdSe Quantum Dots


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A-sorption spectra of !.


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Scanning electron micrographs of (A, TiO2 particulate ;lm caston OT and (10 C0 and D, TiO2 nanotu-es prepared -' electrochemetching of titanium foil. The side 4ie& (1,0 top 4ie&(C,0 and magni;

4ie& (D, illustrate the tu-ular morpholog' of the ;lm

Deposition o QD on Tio2 !lms


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>$"$ nm particles ( diameter,>$"$ nm particles ( diameter,

lectro chemical etching of Ti in ?uoridelectro chemical etching of Ti in ?uorideTio2 nanotu-esTio2 nanotu-es

%$@$ nm ( diameter, 0 % um long%$@$ nm ( diameter, 0 % um long

Photograph of 2.!0 2.=0!.$0 and !.< nm

diameter CdSe7uantum dots

(A,in toluene0(1,anchored on TiO2

particulate ;lms

(OT#TiO2(P,#CdSe0(C, attached to TiO2nanotu-e arra'(Ti#TiO2(9T,#CdSe,.


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"ro#th details"ro#th details

Constant a-sorption monola'erCdSe

inear increase in a-sorption &ithTiO2 thicBness

CdSe 7uantum dots and TiO2 -inding/ -ifunctional linBer molecules (3OOC

C32C32S3,

car-o'late and thiol functionalgroups


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$bsorption spectra$bsorption spectra

A-sorption spectra of (a, !.


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Selecti4el' har4est lightSelecti4el' har4est light

CdSe maintains 7uantizationCdSe maintains 7uantization

properties after -indingproperties after -inding

A-sor-ance E $.


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o oe ec roc em s r% oTiO2 Films &odi!ed #ith

CdSeQuantum Dots Open circuit 4oltageOpen circuit 4oltage Short current circuitShort current circuit Open circuit 4oltage isOpen circuit 4oltage is

same for all. (="$G2$ m6,same for all. (="$G2$ m6, njected electrons rela tonjected electrons rela to

lo&est conduction -andlo&est conduction -and

conduction -andconduction -and

le4el of TiO2G redo E =$$ m6le4el of TiO2G redo E =$$ m6


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Photocurrent response depends onPhotocurrent response depends on

particle sizeparticle size

Photocurrent response of (A, OT#TiO2(9P,#CdSe and (1,(Ti#TiO2(9T,#CdSe electrodes. ndi4idual traces correspond to(a, !.2$ nm0 )$$ mI#cm2J

electrol'te0 $.) : 9a2S solution,.


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:aimum photocurrent:aimum photocurrent!.$ nm CdSe!.$ nm CdSe

T&o opposing e+ects/T&o opposing e+ects/

) decreasing size) decreasing sizeshift of theshift of the

conduction -ad to more negati4econduction -ad to more negati4e

potentialpotentialdri4ing force for chargedri4ing force for charge

injectioninjection2 decreasing size2 decreasing sizesmaller response insmaller response in

4isi-le region4isi-le regionless photocurrentless photocurrent


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6 characteristics of (A, OT#TiO2(9P,#CdSe and (1, (Ti#TiO2(9T,#CdSe electrodes (ecitation H>2$ nmJ intensit' )$$electrol'te0 $.) : 9a2S solution.,Fnder the applied potential charge recom-ination is minimized


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Tuning the Photoelectrochemical'esponse through Size

Quantization( incident photon to charge carrier e+icienc'(PC,

Photocurrent action spectra

A, OT#TiO2(9P,#CdSe and(1, (Ti#TiO2(9T,#CdSe electrodes


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nanotu-e TiO2 ;lms generall' a-sor- more light than nanoparticle TiO2

;lms0 this di+erence accounts for a no more than a "* increase

in o4erall photons a-sor-ed. Comparing this &ith a )$*

impro4ement in PC of the nanotu-e ;lm o4er the nanoparticle ;lm demonstrates the measura-le ad4antage of a nanotu-e

architecture for facilitating electron transport in nanostructure

-ased semiconductor ;lms.


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Design o 'ainbo# SolarCells

Artistic mpression of a 8ain-o& Solar CellAssem-led &ith Di+erentSized CdSe Quantum Dots on a TiO2

9anotu-e Arra'


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ConclusionConclusion

Size dependent charge injection ( Tio2Size dependent charge injection ( Tio2

CdSe,CdSe,

:orpholog' dependence:orpholog' dependence

O4erall po&er e+icienc' of a-out )*O4erall po&er e+icienc' of a-out )*

&ith !nm&ith !nm

CdSe QDCdSe QD

:aimum PC 4alue (>"*, o-tained&ith CdSe#TiO2(9T, is greater than thatof CdSe#TiO2(9P, (!"*,.

(2) quantum dot solar cells

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