7th Korea-US Nano Forum Seoul, April 5-6, 2010

Organic-Inorganic Hybrid Materials for IR-Photodetection and PhotovoltaicsIR-Photodetection and Photovoltaics

20nm

Kwang-Sup LeeD f Ad d M i lDepartment of Advanced Materials,

Hannam University, Daejeon 305-811, Korea

Contents

I d i- Introduction

Quantum Dot based Hybrids- Quantum Dot-based Hybrids * Enhancing the Photocurrent Density* Photopatternable Quantum Dots* Photopatternable Quantum Dots

- Low Bandgap PolymersLow Bandgap Polymers

- C60 Derivatives

- Summary

IR Photodetection

Increase detectivity Increase number of applicationsMedical W hMedical

(Thermal Imaging) WeatherMilitary

Astronomy: Infrared Image of

the Milky Wayy y

Solar Spectrum

(Nanocrystal Quantum Dots)

Pb (Lead)Se (Selenium)Se (Selenium)

PbSe (for IR)CdSe, InP, InP-CdS core-shell

(for visible) Z S CdS (f UV)

• Semiconducting characteristics

• Excellent quantum size effects

ZnSe, CdS (for UV)

• Excellent quantum size effects

• Efficient excitonic generation

• Tunable absorption and emission inTunable absorption and emission in the UV to IR

Tuning of Spectral Response by Choosing Quantum Dots

AbsorptionLuminescence

λ

ZnSe

Broadband Absorber

CdSe, InP

λ

CdSe, InPQuantum Dots

PbSe

λ

CdSe QD20nm

Preparation of PbSe Nanocrystals

Ar

precursors

Thermocouple

organic capping toorganic capping toenable dispersionenable dispersion

Heating mantlemantle

Stir plate reactants + solvent

Semiconductor quantum dotcore-shell/bipods/tripods/ tetrapods

(PbO + Oleic acid in tri n octylamine solvent)+ TOP Se or TBP Se(PbO + Oleic acid in tri-n-octylamine solvent)+ TOP-Se or TBP-Se

Comments: Size and shape control + Surface functionalization of the ti l i t t tparticles are very important steps.

Comparative Environmental Stabilities of IR QDs andIR Organic DyesIR Organic Dyes

Excitation - 720 nmEmission - 830 nm.

Normal laboratory environmental storageenvironmental storage conditions.

Hybrid Materials for IR Photodetection

QD / Pentacene / PVK Polymeric NanocompositePolymeric Nanocomposite

PentacenePentacene

Synthetic Route for Pentacene Precursor

OAli Afzali, et.al, J. Am. Chem. Soc. 2002, 124, 8812.

H3C C N S O+

N-sulfinylacetamidePentacene

O

yPentacene

CH3ReO3 SN

O

CHCl3

Pentacene precursor“Soluble in CHCl3, CH2Cl2

”

Prepared by the Diels-Alder reaction between pentacene & N-sulfinylamide in the presence of a catalytic amount of methyltrioxorhenium,

Device Processing for IR Photodetector

N

O

nSO

Nn

Pentacene precursor PbSe nanoparticle PVK

PVK-Pentacene precursor-PbSe Film Baked in vacuum oven at 240 oC Measured Photoconductivity

Film Composition: PVK 30 wt%, Pentacene precursor 30 wt%, PbSe 40 wt%

Evaluation of Photoconductivity

samplesample

ITOITO

lightlight

ITOITOelectrodeelectrode

focusedfocused

collimatedcollimated

RR

HHVV

Typical I-V Curve

KeithleyKeithley source metersource meter

Photocurrent density as a function of applied voltage in devices with thesame proportion of PVK: pentacene (3:1) but various amounts of PbSesame proportion of PVK: pentacene (3:1) but various amounts of PbSenanocrystals as indicated in the legend.

Appl. Phys. Lett., 87, 051109 (2006) / US Patent 0128021 A1, 2008

Photocurrent density as a function of applied bias (1340 nm) indifferent devices with varying proportions of PVK and pentacene

The photocurrent increases significantly as the amount of pentacene in the composite increasesThe photocurrent increases significantly as the amount of pentacene in the composite increases.The best performance was extracted in devices with equal amounts of PVK and pentacene(having 25 wt % of PbSe QDs). The enhancement in photocurrent, compared to a PVK-PbSefilm, is over 8 times.

Comparison of the external quantum efficiency of the composite devices

2 % f S25 wt % of PbSe

Max EQE: Max EQE: ~ 8% in the IR~ 8% in the IR

A maximum external quantum efficiency (EQE) of ~8% at an applied device bias of 5 V is achieved in the composite having equal amounts of PVK and pentacene. This is an improvement of eight times over the PVK:PbSe devices under similar experimentalimprovement of eight times over the PVK:PbSe devices under similar experimental conditions.

QD-Carbon Nanotube / PVK Polymeric Nanocomposite

Carbon Nanotubes Coupled with Quantum Dots

SWCNT PbS QDSWCNT-PbSe QDs

SWCNT-CdSe

SWCNT CdSSWCNT-CdS

J. M. Haremza et al, Nano Lett. 2, 1253 (2002)

SWCNT-CdSe

S. Banerjee et al, Nano Lett. 2, 195 (2002)

I. Robel et al,Adv. Mater. 17, 2458 (2005)

QD-SWCNT-Polymer Nanocomposites for PhotovoltaicsPhotovoltaics

S A i h hi l AET

QD QDSH

H2N

SH

NH 2

HS

NH 2

HSNH

SHH2NAET

Spacer: Aminoethanethiol: AET

NH 2HS

NH 2

SH

NH 2

SHH2N

COOH

ligandexchange

COOH COOH

SWCNT

carboxylationCOOH

COOHCOOH

COOHCOOH

Dots

A variety of QDs active from UV to IR enables us to accessa wide part of the solar spectrum

b

10 nm10 nm

3 nm

2000

2500

1500si

ty (a

.u.)

1000

PL in

tens

0

500

1000 1100 1200 1300 1400 1500 1600

0

Wavelength (nm)

PL spectra of PbSe QDs (solid line) and SWNT-PbSe (dotted line)in tetracholoethylene colloidal suspensions. The concentration of y pPbSe QDs was the same in both cases.

I-V Characteristics of PbSe QD/PVK and SWNT-PbSe /PVK Devicein Dark and under Illumination

RR

HHVV

Keithley source meterKeithley source meter

b

Adv. Mater., 19, 232-236 (2007) / US Patent 2010-0025662 A1, 2011ACS “Heart Cut” Research Highlight, 2007

Contents

I d i- Introduction

Quantum Dot based Hybrids- Quantum Dot-based Hybrids * Enhancing the Photocurrent Density* Photopatternable Quantum Dots* Photopatternable Quantum Dots

- Low Bandgap PolymersLow Bandgap Polymers

- C60 Derivatives

- Summary

Surface Functionalization for Photo-Patternable QDs

OONH

OO

NH2hv with H+ catralyst

Chemical Amplification Reaction

D

NH

OOS

S

NH

OO

S

SHNS

HN

OO S

NHO

SS

NH2S

S

NH2S

SS

H2N S

H2N

SS

hv with H+ catralyst

ΔQD

QD

HN O

OHNO

O

SHN

OO NH2

H2N

SH2N

Se

Pb

Nano Lett., 8, 3262(2008)

Photocurrent Measurements of Photopatternable QDs

(a) 4

5

CdTe (t-BOC protected)CdTe (Deprotected)

2

3

rent

(nA

)

( p ) Dark

1

2

Cur

r

0 5 10 15 20 25 30 350

Electric Field (MV/m)(b)

Current-voltage curves (a) in the dark or with white light (100 mW/cm2) illumination for a film of t-BOCprotected and deprotected CdTe nanocrystals (measured at the voltage scan rate is 1 V/s). The channel lengthis 5 μm. MSM device structure (b) for photoconductivity measurement.

Polymer Nanocomposite Photovoltaics utilizing CdSe QDs Capped with a Thermally Cleavable Solubilizing Ligand

P3HT: CdS i

Al

PEDOT

P3HT: CdSe-amine

ITO

1.0

1.5

/cm

2 )

0 01

0.1

1

nsity

(mA

/cm

2 )

Solar Cell Device Structure

0.0

0.5

sity

(mA

/

0.0 0.2 0.4 0.6 0.8 1.0

1E-3

0.01

Cur

rent

den

Voltage (V)

1 0

-0.5

rent

den

s

100 oC (photo)100 oC (dark)

Thermal cleavage oft-BOC

0.0 0.2 0.4 0.6 0.8 1.0-1.5

-1.0

Cur

r 100 C (dark) 200 oC (photo) 200 oC (dark)

Voltage (V)Appl. Phys. Lett., 94, 133302 (2009)

OO

SiO

O O

O

Si

O

O

SiOSi

O

O

O

SiO

O

OS

SS

S

CdSe11

11

11

11

O

O

11

QD 1

UV: 552nm

PL: 568nm

3-D Lithographic Microfabrication

♦ Localized photochemistry by TPA process

C i PolymerizedCollimated Laser BeamPhotocurable film

Polymerizedregion

Objective lens

Focused beam

Lens

Single-photonpolymerization

Two-photonpolymerization

j

TPA : volume of order λ 3

Lens

TPA : volume of order λDOFLocalized photo-

polymerizationWidth

polymerization

Use of longer radiation wavelengths in TPA process is possible to achieve the better Use o o ge ad at o wave e gt s p ocess s poss b e to ac eve t e bettepenetration depth in the medium

S

SSPVDTT Flu PE

RR

N

RR

RR

RR

RR

RR

RR

RR

RR

R

RR

RR

N

SS

S

SS

NN

OC12H25

C12H25O

OC12H25

C12H25O

NBu2-DTTPE-NBu2 RRR

Polymers CeramicsNBu2-DTTPE-NBu2

MetalsMetals

CdSe/ZnSCore-Shell

CdSe

Figure (a) shows the  photocuring of working acrylate functionalized quantum dots with its layer structure, (b) Shows the synthesis scheme for the acrylate functionalized photopatternable quantum dots.

Photopatterns by Using CdSe/ZnS Core-Shell QDsClli t dL B PolymerizedCollimated Laser Beam

L

Single-photonpolymerization

Two-photonpolymerization

Photocurable film

Polymerizedregion

Objective lens

Focused beam Size distribution of Nanorods: 10 -30 nm

TPA : volume of order λ3

Lens

DOFLocalizedphoto

Width

Localized photo-polymerization

Polymer Blocking Layer Effect on In2S3/CuInSSe Solar CellPEDOT:PSS

-5

0

5

2 ) -

eV

PEDOT:PSSBlocking the back recombination

-

-15

-10

-5

sity

(m

A/c

m2

+

-Ec

EF

-4

-5

-3

Au+

-

-25

-20

Cur

rent

Den

s

InS/CISSe/A

Ev

TiO In SCuInS2, CuInSe2

-6

-7

-8

Au

-0.1 0.0 0.1 0.2 0.3 0.4-35

-30C

Voltage (V)

InS/CISSe/Au InS/CISSe/PEDOT:PSS/Au

TiO2 In2S3 or CuInSSe

V is similarg ( )

Voc(V) Jsc(mA/cm2) FF(%) PCE(%)

Voc is similarJsc shows significant increaseFF is decreasedPCE increases due to the Jsc increment( )

w/o PEDOT:PSS ~0.26 18.4 35.3 1.69

with

PCE increases due to the Jsc increment

PEDOT:PSS effectively blocks electrons & transports holeswith

PEDOT:PSS ~0.29 33.5 31.9 3.16electrons  & transports holes 

Prasad et.al, 2009

Low-Bandgap Conjugated Polymersg p j g y

S S

NSN

nS

n

A

PCPDTBTn

P3HT

D-A concept Rigiospecific Structure

Optical Bandgap: 1.52 eV 1.90 eV

Low Bandgap Conjugated Copolymers: PFTB & PCTB

S S S

NS

N

S

PFTB PCTB

N

C8H17C8H17S

N

C8H17C8H17 NS

NS

C6H13

m n

R = C8H17: R1 = C6H13 n=0.1, m=0.9SR R R1 R1R Rn m

R = C8H17: R1 = C6H13 m=0.9, n=0.1S S S

C6H13l

n

Abs: λmax PL : λmaxAbs: λmax PL : λmax Abs: λmax PL : λmax521 nm 642 nm 519 nm (with PCBM 1:4) 643 nm (with PCBM 1:4)

Abs: λmax PL : λmax521 nm 642 nm 519 nm (with PCBM 1:4) 642 nm (with PCBM 1:4)

)

DeviceJsc Voc FF Solar Efficiency

2

-2

0

ent D

ensi

ty (m

A/c

m2

P3HT

I-V Characteristics and Solar Cell Efficiency

Device (mA/cm2) (V) (%) (%) P3HT/PCBM

(1:0.8) 4.234 0.485 49.68 1.02 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

-4Cur

r

Voltage (V)

P3HT PFTB:PCBM (1:4)

)

PFTB/PCBM3.596 0.881 37.64 1.19

(1:4) PCTB/PCBM

3 782 0 862 38 74 1 26-2

0

Den

sity

(mA

/cm

2 )

3.782 0.862 38.74 1.26(1:4)

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

-4 P3HT PCTB:PCBM (1:4)C

urre

nt

Voltage (V)

Development of Efficient NIR Polymers;Synthesis of the Low bandgap Polymers

NSN NSN

SNSN

Synthesis of the Low bandgap Polymers

n

NS S

PFTTBTS S

NN

n

N SN

SSn

NS S

NS N

PFTTBBT

S S

NSN

nPCPDTBT

PCPDTBBT

0 30

0.35

PFTTBTPCPDTBT Optical properties of various polymers

0 20

0.25

0.30

(a.u

.)

PCPDTBT PFTTBBT PCPDTBBT Polymer Abs.

λmax. Opt. band

gap

PFTTBT 530 nm 1 98 eV

0 10

0.15

0.20

Abs

orba

nce PFTTBT 530 nm 1.98 eV

PCPDTBT 718 nm 1.52 eV

0 00

0.05

0.10A PFTTBBT 868 nm 1.19 eV

PCPDTBBT 950 nm 0.92 eV

400 600 800 1000 1200 14000.00

Wavelength (nm)

Comparison of UV-vis Absorption of Low Bandgap Polymers

BPCPDTBT (by Heeger’s group)

S S

S SBu3Sn SnBu3 Polymerization (Stille coupling)

NSN

NSN

SNSN

N NSBr

Sn

S BrPCPDTBBTB

2

PCPDTBT film PCPDTBT-PCBM blend film PCPDTBBT film N

SN

NSN

ce (

a.u.

) PCPDTBBT-PCBM blend filmSS

N

n

1

Abs

orba

nc 1100 nm

NS

PCPDTBBT (Our Work)

0

A

SS S S

NN

nN S

N

400 600 800 1000 1200 14000

Wavelenth (nm)

S

37

UV-vis absorption spectra of the PCPDTBT and PCPDTBBT Polymer films and the polymer-PCBM blend films

Contents

I d i- Introduction

Quantum Dot based Hybrids- Quantum Dot-based Hybrids * Enhancing the Photocurrent Density* Photopatternable Quantum Dots* Photopatternable Quantum Dots

- Low Bandgap PolymersLow Bandgap Polymers

- C60 Derivatives

- Summary

C60 Derivatives as Acceptors in Hybrid Bulk Heterojunction Solar Cells

PCBM

(A) (B)

Fig. (A) The contour plots of the HOMOs (left side) and the LUMOs, right side) of all investigated dyads.investigated dyads. (B) Electronic energy levels of an isolated dyads. Vertical arrows represent the most probable transitions (with oscillator strength higher than 0 1 Blue red andhigher than 0.1. Blue, red, and green arrows corresponds to the LE(F), LE(T), and ICT transitions, respectively.

Chem. Phys. Lett. 479 , 224 (2009) / Synth. Met. 159, 2539 (2009)

Electron Mobility of New n-Type C60 Derivative (Fu-Hexyl)

Encap glass

NS

S D

OSC

getterAl

Inkjet printing (0.5wt% Fu-Hexyl in chlorobenzene)

Fu-Hexyl

n+ SiGate (SiO2)

Mgchlorobenzene)

μ=0.028 cm2/V·s (0.0058 cm2/V·s for PCBM)

On-off ratio = 1.9 × 105

Org. Electron, 10, 1028 (2009)

Efficiency of ITO/PEDOT:PSS/P3HT:C60 Derivative/TiOx/Al Solar Cells

0

2

cm2 )N

S

-4

-2

sity

(m

A/c

-10

-8

-6

rren

t Den

s

P3HT:PCBM P3HT:C60-TH-Hx-3

P3HT:C60-TH-Hx-5

0.0 0.2 0.4 0.6 0.8-12C

ur

Voltage (V)

P3HT:C60-TH-Hx-5

Fu-Hexyl

Compounds Jsc (mA/cm2) Voc (V) FF Eff (%)

P3HT:PCBM 6.32 0.582 0.65 2.39

P3HT:C60-TH-Hx-3 6.58 0.575 0.64 2.44

Graphic Summary

Profs Paras N Prasad & Alex N Cartwright

Coworkers

Profs. Paras N. Prasad & Alex N. Cartwright Institute for Lasers, Photonics and Biophotonics, Univ. at Buffalo, SUNY, Buffalo, USA

Prof. Andrzej Graja j jPolish Academy of Sciences, Poznan, Poland

Prof. Tae-Dong Kim Dept of Advanced Materials Hannam Univ Daejeon KoreaDept. of Advanced Materials, Hannam Univ., Daejeon, Korea

Funding Agenciesg g

KRFKRF KOSEF AOARD / AFOSRSamsung Electronics