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Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov

Physics of Organic Semiconductor Devices: Materials, Fundamentals, Technologies and Applications

Dr. Alex ZakhidovAssistant Professor, Physics Department

Core faculty at Materials Science, Engineering and Commercialization Program.

http://zakhidov.wp.txstate.edu/

http://zakhidov.wp.txstate.edu/


Outline

1. Why organic electronics and what is it good for?

2. How to save the world with organic perovskite solar cells?


Organic LightEmitting Diode (OLED)

Organic Thin FilmTransistor (OTFT)

Organic Solar Cell(OSC)

Samsung

Heliatek

Organic Electronics Devices: Smart, Flexible, Cheap!

Other devices: organic lasers, organic memory, organic bio(chemical) sensors


Chemistry

Phys

ics

EngineeringM

aterialsScience

Chemistry

Phys

ics

EngineeringM

aterialsScience

New material synthesis:design, polymers, small molecules

Enabling technologies:Processing, patterning, doping,

encapsulation

Fund

amen

tals

, mec

hani

sm o

f op

erat

ion,

new

dev

ice

conc

epts

“Evolution” of organic electronics

Materials (1960-70)

First devices (late 1980s)

OLEDs Used for mobile displays and TVs

(2012)

Commercial prototypes(2000s)

progress

Materials properties:

Mobility, optical properties,

Structure, film m

orphology


S.R. Forrest ,Nature 428 (2004)

Organic compounds contain carbon


Organic Semiconductors – π - conjugated organic molecules

linear

aromatic


Organic Semiconductors – π - conjugated organic molecules

In 1977, they discovered that polyacetylene can be oxidized with halogens to produce conduct ing materials f rom either insulat ing or semiconduct ing materials.

+ I


General Features of Organic Semiconductors

Advantages Challenges

1. Unlimited material design options

2. Varity of structures and morphologies

3. Band gap engineering

4. Light, flexible, inexpensive

5. Electronic and Ionic transport*

6. Disorder: highly localized exciton

1. Device engineering. (Lithography,

Doping, Materials purity, Horizontal and

vertical integration)

2. Stability, Lifetime

3. Organic/Inorganic Interfaces

4. Disorder: highly localized charge carriers

10nm 100nm 1µm

L

10 µm 100 µm 1 mm1 nm

lamellaamorphous microcrystalline crystallinenano-crystalline

*Al.A. Zakhidov, B. Jung, J.D. Slinker, H.D. Abruña, G.G. Malliaras, “A light-emitting memristor”, Organic Electronics 11, 150 (2010).


Electronic properties of Organic Semiconductors

10-6 10-5 10-4 10-3 10-2 10-1 1 10 102 103 104 105

Amorphous Highly crystalline

Organic semiconductors

a-Si Mobility cm2/Vs

p-Si

CMOS

Graphene

GaAs, InSb, GaN,

InAs

*Y. Yuan, et al Nature Communications 5 (2013).

T. Sekitani, et. al. Nature Materials 9 (2010)

H. Klauk, Chemical Society Reviews, 39 (2010 )

Lens to monitor glucose level in tear

Google

Organic semiconductors


Optical properties of Organic Semiconductors

Molecular pictureSemiconductor picture

Binding energy ~ 1 eVRadius ~ 10 Å

Ground State Ground StateFrenkel exciton WM exciton

kbTroom~26 meV

Binding energy ~ 10 meVRadius ~ 100 Å

Organics: Frenkel excitons Inorganics: Wannier-Mott excitons

εorg<< εinorg

Eex=e2/(ε·rex)


Happy Life…


How much do we need?

Eco Friendly

In fact can help us to “deal” with global climate change


Why are we not doing this already?


$$$$

$$$

$$ 20%

$, but….

National Renewable Energy Lab Solar chart


Perovskite structure and processing

CH3NH3I + PbX2

Where X - Br, I or Cl.

Organic precursor

Inorganic precursor

Spin/dip-coating

Vacuum co-deposition

CH3NH3

XPb

ITO/FTOElectron Selective layer

perovskite absorber

Generic perovskite solar cell

Hole Selective layerAg

Perovskite layer top view


Organic Perovskite Solar Cells

Advantages Challenges

1. Efficiency >20%

2. High optical absorption

3. Low recombination rates

4. High carrier transport mobility

5. Tunable band gap

6. Room temperature processing

7. Low-cost, abundant materials

1. Stability

2. Replacement of lead with tin

3. Reliable, scaled-up production

The Energy Pay Back Time EPBT = Einput/Esaved

organic solar cells


Take home message

Physics of Organic Semiconductor Devices: Materials ... › wp.txstate.edu › dist › ...Physics...

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