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Fabrication and Characterization Fabrication and Characterization

• f Organic Semiconductors

f U i Ph t lt i for Use in Photovoltaics

D t t f Ch i l E i i Department of Chemical Engineering

Eric Bonaventure

Chris Carach – Mentor

*Funded by*

• Prof. Michael Gordon – P.I.

Why Are Organic Semiconductors Important? Important?

Silicon Solar Cell Organic Solar cell

• Silicon needs to be purified to
• Easy to mass produce…much cheaper

p 99.9999% (no impurities/defects)

• Time and energy to produce Si

is costly

• Materials defects/impurities are

tolerable is costly

• Payback time can take many

years

• Flexible substrates, large area solar cells

Why Are Organic Semiconductors Important? Important?

Silicon Solar Cell Organic Solar cell

• Silicon needs to be purified to
• Easy to mass produce…much cheaper

p 99.9999% (no impurities/defects)

• Time and energy to produce Si

is costly

• Materials defects/impurities are

tolerable is costly

• Payback time can take many

years

• Flexible substrates, large area solar cells

However, efficiencies are low… processing really affects film morphology Understanding organic semiconductors at multiple length scales (device-level to nano) is a key to increasing efficiency

What is my role in the research?

Electrode

P3HT

hv e‐

OMe O

Semiconductor

P3HT

donor

PCBM

acceptor

S n

Glass Transparent Conductor

• Fabricate different varieties of solar cells
• Develop a “protocol” to create the cells
• Test cells and analyze their respective IV curve
• Test cells and analyze their respective IV curve.

(Current vs. Voltage)

V lt

“Dark Current”

Voltage Source

*Should see current*

Voltage Source

V V

Negative Solar cell Positive current

Positive Solar cell Negative

Negative

I

Ammeter

Positive

I

Ammeter *Should not see current* Ammeter see current

• Conduct a voltage sweep

Ideal Diode Curve

g p

• Does current move both

directions?

• Does the solar cell work?
• Does the solar cell work?

Forward bias Reverse bias

Photocurrent Test With M h Monochromator

• Monochromator turns white

V lt

light (all colors) into one color

• Can test what wavelength

Voltage Source

V

• Can test what wavelength

(color) of light is most efficient

Positive Solar cell Negative Positive

A

Light

A

Ammeter Fiber optic cable cable

Photocurrent Results

IV Curve

20 40

[uA]

‐1 ‐0.5 0.5 1

Current [

40 ‐20 1 0.5 0.5 1

C

Dark Current

‐60 ‐40

Dark Current 100 Percent Intensity

Voltage [V]

Photocurrent Results

IV Curve

Useable energy created from light

20 40

uA]

created from light

1 0 5 0 5 1

urrent [u

‐20 ‐1 ‐0.5 0.5 1

C

Dark Current

‐60 ‐40

Dark Current 100 Percent Intensity

Voltage [V]

Photocurrent Results

IV Curve

20 40

[uA]

increasing light intensity ‐1 ‐0.5 0.5 1

Current [

40 ‐20 1 0.5 0.5 1

C

Dark Current

‐60 ‐40

10 Percent Intensity 25 Percent Intensity 50 Percent Intensity

Voltage [V]

100 Percent Intensity

Conclusions

• Polymer dissolution was critical in spinning high

quality films quality films

• Slowing down solvent evaporation during and

ft i ti f t l h i after spin coating fosters polymer chain

• rganization → increases charge transport

efficiency

• P3HT/PCBM device with PCBM overlayer gave the

best performance best performance

• Oxidative damage to the conjugated polymer

inhibited charge transport inhibited charge transport

Future Research

N l Ch t i ti

~Nanoscale Characterization~

Topographical analysis with Atomic Force Microscopy

Future Research

N l Ch t i ti

~Nanoscale Characterization~

Topographical analysis with Atomic Force Microscopy

Topography of semiconducting film

0nm 750nm

Future Research

N l Ch t i ti

~Nanoscale Characterization~

Topographical analysis with Atomic Force Microscopy

Topography of semiconducting film Material PCBM crystal Material heterogeneity at nano/micro scale is observable! Well-mixed

0nm 750nm

Future Research

N l Ch t i ti

~Nanoscale Characterization~

Analyze point‐by‐point current reading with Tunneling AFM (TUNA) Nanoscale IV measurement…at every point!

Future Research

N l Ch t i ti

~Nanoscale Characterization~

Analyze point‐by‐point current reading with Tunneling AFM (TUNA)

Nanoscale IV measurement…at every point! +30V Tip Bias

Tunneling Current Current

10μm

850pA 150pA

Perspective Perspective

Macroscopic testing shows us a good vs bad solar Macroscopic testing shows us a good vs. bad solar cell…but not the why

Perspective Perspective

Macroscopic testing shows us a good vs bad solar Macroscopic testing shows us a good vs. bad solar cell…but not the why We need to understand more about nanoscale interactions to produce higher efficiencies

Perspective Perspective

Macroscopic testing shows us a good vs bad solar Macroscopic testing shows us a good vs. bad solar cell…but not the why We need to understand more about nanoscale interactions to produce higher efficiencies Correlating macroscale performance with nanoscale Correlating macroscale performance with nanoscale morphology is necessary to understand and engineer better organic semiconducting materials and solar cells

Acknowledgements

Chris Carach

• Prof. Michael Gordon

F di f

*All the Gordon Group Gophers*

Funding from

Dark Current vs Photocurrent Diode Curve Photocurrent Diode Curve (Dark Current) Photocurrent (Just from light)

PV Stack PV Stack

Electrode P3HT/C60 C60 ITO PEDOT/PSS Glass

Efficiency Efficiency

=

100 mW/cm2

Power = I * V Power = Current * Voltage Efficiency = = Power Current Voltage Efficiency =

The Monochromator

Set up for photocurrent test

The solar cell The solar cell

Shine light to excite an electron Exciton Pair Split exciton Pair to induce current

LUMO (P3HT)

electron flow

LUMO (PCBM) ITO ALUMINIUM

+

HOMO (P3HT)

e‐

HOMO (P3HT) HOMO (PCBM)

Current Density vs Voltage

100

• 200
• 100
• 0.4
• 0.3
• 0.2
• 0.1

0.1 0.2 0.3 0.4

[uA/cm 2]

600

• 500
• 400
• 300

t Denisty [ Dark Current

900

• 800
• 700
• 600

Curren Photocurrent

• 900

Voltage [V]

Power Overview

IV Curve

Power Overview

Power = Current * Voltage

10 20

A] g

10 ‐1 1

rrent [uA Current equals

‐20 ‐10 ‐1 1

Cur

Dark Current Photocurrent

zero

40 ‐30 Photocurrent ‐40

Voltage [V]

Power Overview

IV Curve

Power = Current * Voltage

Power Overview

10 20

A] g

10 ‐1 1

rrent [uA

‐20 ‐10 ‐1 1

Cur

Dark Current Photocurrent

Voltage equals

40 ‐30 Photocurrent

g q zero

‐40

Voltage [V]

Power Overview

IV Curve

Power Overview

Power = Current * Voltage

10 20

g

Intentisty graph

10 ‐1 1

[mA] M i

‐20 ‐10 ‐1 1

Current [

Dark Current Photocurrent

Maximum power!!!

40 ‐30

C

Photocurrent ‐40

Voltage [V]

Analyzing Results

IV Curve IV Curve

100

A]

20 40

u]

‐200 ‐100 ‐1.00 0.50

rrent [nA

20 ‐1 1

ent [mu

‐400 ‐300

Cur

‐40 ‐20 ‐1 1

Curr

‐600 ‐500 Dark Current Photocurrent 80 ‐60 Dark Current Photocurrent ‐700

Voltage [V]

‐80

Voltage [V]