1

Material and Structural Designfor High Efficiency Dye-Sensitized Solar Cell

Hyungjun Koo, Beomjin Yoo, Kicheon Yoo, Kyungkon Kim and Nam-Gyu Park*

Center for Energy MaterialsKorea Institute of Science and Technology

(KIST)

N

N

C

C

O

O

HO

N

N

C

C

O

O

O

HO

RuNCS

NCS

O

The 4th US-Korea NanoForum

2

DSSC: structure and operation principle

D*/D+

D/D+

CB

VB

I3¯/I¯surface states

Voc

TiO2 Dye

τinj

τcc

τr

TCO

TiO2

N

N

C

C

O

O

HO

N

N

C

C

O

O

O

HO

RuNCS

NCS

O

3

issues

Efficiency (η) = (JscⅹVocⅹFF)/Pin

Case1: JSC increased by 30%1000.740.7518 → 23.410 →

13

cf.PinFFVocJscη (%)

Case2: VOC increased by 30%1000.740.75 → 0.981810 →

13

cf.PinFFVocJscη (%)

Efficiency (η) = (JscⅹVocⅹFF)/Pin

13%

13%

* efficiency as high as 11% has been achieved.* higher efficiency is required in order to be in competition with Si solar cell

Approaches for improving efficiency

4

light confinement by scattering:

size-dependent scattering efficiency &bi-functional material

structural and material design

strategy for improving JSC

5

nanoparticle films for DSSC

180 190 200 210 220 230 2407.0

7.5

8.0

8.5

9.0

Effic

ienc

y (%

)

Autoclave Temp. (oC)

210 220 230 2407.0

7.5

8.0

8.5

9.0

Effic

ienc

y (%

)

Autoclave Temp. (oC)

t = 5-6 µm t = 10-12 µm

Simple increase of nanoparticle film may not improve the efficiency to great extent!

6

(a) G1 (b) G2

20 25 30 35 40 45 50 55 60

(b)

R(2

20)R

(211

)

R(2

10)

R(1

11)

R(2

00)R

(101

)R(1

10)

A

***

A

Inte

nsity

(a.u

.)

2θ (degree)

(a)

size-dependent scattering efficiency

SL

7

+16.3%8.78 ± 0.0970.7 ± 0.4866 ± 114.4 ± 0.11L+G2

+18.4%8.94 ± 0.0870.4 ± 0.3852 ± 214.9 ± 0.01L+G1

7.55 ± 0.1271.1 ± 0.1868 ± 212.2 ± 0.11L (~7 µm)

Increasing rateEff. (%)FF (%)Voc (mV)Jsc

(mA/cm2)

PV properties

400 500 600 700 8000

20

40

60

80

IPC

E

Wavelength

1 L 1 L+G1 1 L+G2

8

400 500 600 700 8000

20

40

60

80

100

Ref

lect

ance

(%)

Wavelength (nm)

nano-TiO2 film G1 film G2 film

reflectance spectra

nano-TiO2thin filmunderlayer

scatteringoverlayer

9

bi-functional material* spherical or flat surface large particles are normally used for light scattering

* except light scattering, such materials do not contribute to photocurrent generation due to low surface area

* motivation: design of bi-functional material exhibiting both light scattering and photocurrent generation efficiently

Nano-Embossing Hollow Sphere TiO2(prepared by Prof. W.-I. Lee)

300 nm300 nm300 nm

10

IPCE & reflectance comparison

400 500 600 700 8000

20

40

60

80

IPC

E (%

)

Wavelength (nm)

2L 1L-NeHS 1L-CCIC

400 500 600 700 800 9000

20

40

60

80

100(b)

%R

Wavelength (nm)

CCIC TiO2 Particle Film NeHS TiO2 Film nanocrystalline TiO2 Film

1L

NeHS

11

conversion efficiency

0.0 0.2 0.4 0.6 0.80

5

10

15

20

Phot

ocur

rent

den

sity

(m

A/c

m2 )

Voltage (V)

JSC : 17.8 mA/cm2

VOC : 0.845 V FF : 0.69 η : 10.34%

without long-term post-treatment of TiCl4

12

interfacial nano-engineering

13

locus of recombination

bulkrecombination

near substraterecombination

14

methods for suppression of recombination

Mesoporous electrode

blocking layer

TiO2

FTO

TiO2FTO

core-shell

(to protect bulk recombination)

(to protect recombination at near substrate)

15

FTO/BL/TiO2: SEM

300nm

Bare

0.15 M

0.4 M

300nm

Blocking layer

TiO2FTO

Chemically formed from Ti precursor solution

16

effect of Ti-precursor concentration on PV property

0.0 0.2 0.4 0.6 0.8

12.6

12.8

13.0

13.2

13.4

0.0 0.2 0.4 0.6 0.80.80

0.82

0.84

0.86

0.88

0.0 0.2 0.4 0.6 0.80.70

0.72

0.74

0.760.0 0.2 0.4 0.6 0.8

7.6

7.8

8.0

8.2

8.4

J SC (m

A/c

m2 )

VO

C (V

)

Ti precursor concentration (M)

FF

η (%

)

measuredunder mask with aperture

17

EIS (bode plot)

10-2 10-1 100 101 102 103 104 105 1060

-10

-20

Frequency, Hz

Thet

a

100 101 102 103 104

0.8M

0.4M0.2M

0.15M0.1M0.05Mbare

CB A

2nd

deriv

ativ

e th

eta

(arb

t. un

it)

Frequency, Hz

A: pt/electrolyte; B: FTO/electrolyte; C: TiO2/dye/electrolyte

0

-5

Cole-Cole

Bode

0.0 0.5 1.010-5

10-4

10-3

Inve

rse

freq

uenc

y (1

/Hz)

Precursor concentration (M)

A

0.0 0.5 1.010-4

10-3

10-2

Precursor concentration (M)

Inve

rse

freq

uenc

y (1

/Hz)

B

0.0 0.5 1.010-2

10-1

Precursor concentration (M)

Inve

rse

freq

uenc

y (1

/Hz) C

Hz

Hz

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Surface modification of bulk TiO2 film: fast electron transport, slow recombination

10-2 10-1 100

10-3

10-2

10-1

photocurrent transient

Tim

e (S

)

Photocurrent Density(mA/cm2)

bare TiO2 Photocurrent Photovoltage

TiO2 treated with TiCl4(9hr) Photocurrent Photovoltage

photovoltage transient

Transient photocurrentτTiCl4 treatment < τTiO2

⇒ Enhanced electron transport by TiCl4 treatment

Transient photovoltageτTiCl4 treatment > τTiO2

⇒ Reduced recombination from TiO2 to electrolyte by TiCl4 treatment

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DSSC best efficiency

0.0 0.2 0.4 0.6 0.8 1.002468

10121416182022

Phot

ocur

rem

t den

sity

(m

A/cm

2 )

Voltage (V)

Jsc = 19.38 mA/cm2

Voc = 0.877 VFF = 0.647Eff. = 11%@ AM 1.5G-1 sun

Reference cell: NREL-calibrated mono Si with KG-5 filter

close to the world best efficiency of 11.1% from EPFL

20

PCBMP3HT

Kim et. al., APL 90, 163511 (2007)

Thickness: D1<D2<D3

Max. Eff. of 6.1% was obtained from D2

KIST Activity: Organic Photovoltaics

21

Acknowledgments

KIST Specialists Laboratory for Dye-Sensitized & Organic Solar Cells$$$: KIST, MOST and MOCIE

HJ. Koo NJ. Myung

SY. Bang, MS

KC. Yoo KT. Lee, staff

KW. Lee, MS

TR. Lee

BJ. Yoo, Ph.D.

MA. Lee, MS

Dr. K Kim, Senior Scientist