1

What is graphene?

Q1. How thick is it? a million times thinner than paper (The interlayer spacing : 0.33~0.36 nm)

Q2. How strong is it? stronger than diamond (Maximum Young's modulus : ~1.3 TPa)

Q3. How conductive is it? better than copper (The resistivity : 10−6 Ω·cm) (Mobility: 200,000 cm2 V-1 s-1)

In late 2004, graphene was discovered by Andre Geim and Kostya Novoselov (Univ. of Manchester).- 2010 Nobel Prize in Physics

But, weak bonding between layersSeperated by mechanical exfoliation of 3D graphite crystals.

2

Carbon

Molecular structure of graphene

2D graphene sheet

bucky ball CNT 3D graphite

Electrons move freely across the plane through delocalized

pi-orbitals

3

Electronic structure of graphene

K

EfK

K’

K’

Pz bondingValence band

Pz anti bondingConduction band

2DEG

Fermi energy

Effective mass (related with 2nd derivative of E(k) ) MasslessGraphene charged particle is massless Dirac fermion. Zero gap semiconductor or Semi-metal

4

Electrical properties of graphene

High electron mobility at room temperature: Electronic device. Si Transistor, HEMT devices are using 2D electron or hole.

μ (mobility) = vavg / E (velocity/electric field)

Jdrift ~ ρ x vavg

5

Optical properties of graphene

Optical transmittance control: transparent electrodeReduction of single layer: 2.3%

F. Bonaccorso et al. Nat. Photon. 4, 611 (2010)

6

Mechanical properties of graphene

Young’s modulus=tensile stress/tensile strainDiamond ~ 1200 GPa

Force-displacement measurement

Mechanical strength for flexible and stretchable de-vices

C. Lee et al. Science 321, 385 (2008)

7

Graphene growth by chemical vapor depo-sition

SiC sublima-tion

Metal catalysis

Pros&Cons

High temperature growth :1200~1500°CNon-uniform growth in Step edge and terrace.High cost SiC wafer : SiC growth on SiNo transfer required

Nat.mat.2009.203. Ar1atm,1450~1650°CTerrace size increase.

CurrentStatus Solid Carbon : Low temp.

Nat.2010.549. ACS nano,2011

CVD Ni: non uniform multi Cu: uniform sin-gle Cu: layer by layer growth

Low temperature growth :below 1000°C Unform growth : Capet like (Large area)Si CMOS compatible process. “Transfer required”

8

Large area graphene

K. S. Kim et al. Nature 457, 706 (2009) S. Bae et al. Nat. Nano. 5, 574 (2010)

9

PSCs with graphene anodes

b

0.0 0.2 0.4 0.6

-12

-8

-4

0

IPC

E (%

)

400 600 8000

25

50

CT DT

Cur

rent

den

sity

(mA

cm

-2)

Voltage (V)

(nm)

a

5.1

3.3

Al

4.3

TiOx

8.0 eV

6.0

4.3

PC71BM

5.4

GR/PE-DOT:

PSS (DT)

4.3

5.0

PTB7-F40

PEDOT:PSS

PCE (%)

Device Substrate Electrode Method Voc (V) Jsc (mA cm-2) FF Average Best

PSC

Glass

ITO RF sputtering 0.68 14.1 0.61 5.80 ± 0.06 5.86

GRCT 0.65 11.1 0.55 2.69 ± 1.80 3.92

DT 0.68 12.1 0.67 4.85 ± 0.24 5.49

PETITO RF sputtering 0.64 14.3 0.52 4.52 ± 0.18 4.74

GR DT 0.64 12.5 0.60 4.57 ± 0.21 4.81

10

PLEDs with graphene anodes

5.4

2.4

4.8 eV

4.3

Ca

2.9

5.1GR/PEDOT:

PSS (DT)

SY AlPEDOT:PSS

OR

RO

OR'

OR'

xy

z

0 2 4 6 8 10 12 140

50

100

150

200

250

0 500

4

CT DT

Cur

rent

den

sity

(mA

cm

-2)

Voltage (V)

CE

(cd

A-1)

J (mA cm-2)

-3 0 3 6 9 120.0

0.4

0.8

1.2

1.6

2.0

0 5 10

101

103

CT DT

Lum

inou

s ef

ficie

ncy

(lm W

-1)

Voltage (V)

L (c

d m

-2)

V (V)

11

PLEDs with graphene or ITO anodes

-2 0 2 4 6 8 10 120.0

0.4

0.8

1.2

1.6

2.0

ITO GR/PEDOT:PSS (DT)

Lum

inou

s ef

ficie

ncy

(lm W

-1)

Voltage (V)

2 cm

0 2 4 6 8 10 120

50

100

150

200

250

0 5 10

101

103

Cur

rent

den

sity

(mA

cm

-2)

Voltage (V)

L (c

d m

-2)

V (V)

Device Substrate Electrode Method LEmax (lm W-1) CEmax (cd A-1) VT (V) Lmax (cd m-2)

PLED Glass

ITO RF sputtering 1.87 5.15 4.5 4750

GRCT 1.37 3.69 4.5 3150

DT 1.87 4.14 4.0 4000