Optical Spectroscopy of Organic Solar Cell Materials Jose Cruz - - PowerPoint PPT Presentation

Optical Spectroscopy of Organic Solar Cell Materials

Jose Cruz

Ventura College Chemistry Major Mentor: Chris Carach Faculty Advisor: Dr. Mike Gordon Funding Sources: National Science Foundation

exposolar.org

The Big Picture – Energy

The Big Picture – Energy

• Energy demands satisfied by

nonrenewable sources

U.S. Energy Information Administration

The Big Picture – Energy

• Energy demands satisfied by

nonrenewable sources

U.S. Energy Information Administration

When will fossil fuels reserves be depleted? Crude oil ~ 35 years Gas ~ 37 years Coal ~ 107 years

Shafiee and Topal Energy Policy, 37, 181 (2009)

The Big Picture – Energy

• Energy demands satisfied by

nonrenewable sources

• Solar energy holds potential to be

widely implemented on a large scale

U.S. Energy Information Administration

When will fossil fuels reserves be depleted? Crude oil ~ 35 years Gas ~ 37 years Coal ~ 107 years

Shafiee and Topal Energy Policy, 37, 181 (2009)

The Big Picture – Energy

• Energy demands satisfied by

nonrenewable sources

• Solar energy holds potential to be

widely implemented on a large scale

• Inorganic Photovoltaics

– High production costs – Some contain toxic elements (lead, cadmium)

U.S. Energy Information Administration

When will fossil fuels reserves be depleted? Crude oil ~ 35 years Gas ~ 37 years Coal ~ 107 years

Shafiee and Topal Energy Policy, 37, 181 (2009)

The Big Picture – Energy

• Energy demands satisfied by

nonrenewable sources

• Solar energy holds potential to be

widely implemented on a large scale

• Inorganic Photovoltaics

– High production costs – Some contain toxic elements (lead, cadmium)

• Organic Photovoltaics

– Produced cheaply (roll-to-roll processing) – Environmentally friendly

U.S. Energy Information Administration

When will fossil fuels reserves be depleted? Crude oil ~ 35 years Gas ~ 37 years Coal ~ 107 years

Shafiee and Topal Energy Policy, 37, 181 (2009)

Research Goals

• Understand how the

processing of the solar cell materials affects optical properties and morphology

Poly-3-Hexylthiophene Phenyl-C61-Butyric Acid Methyl Ester

Research Goals

• Understand how the processing
• f the solar cell materials affects
• ptical properties and

morphology

– Absorption of light

• More absorption =

better solar cell Photoluminescence and Absorption Spectra

Absorption Io It

Research Goals

• Understand how the processing
• f the solar cell materials affects
• ptical properties and

morphology: – Absorption of light

• More absorption = better solar

cell

– Alignment of the polymer chains

• Better alignment =

better charge transport

PL

Research Goals

• Understand how the processing
• f the solar cell materials affects
• ptical properties and

morphology – Absorption of light

• More absorption = better solar

cell

– Alignment of the polymer chains

• Better alignment = better

charge transport

– Mixture of the polymer and fullerene

• Better mixing = better

solar cell

Step 1: OPV Film Production

Experimental Methods

Dissolve & Spin Coat Thin Film Formed Solvent Anneal (3 hours) Put in dessicator

Step 1: OPV Film Production

Experimental Methods

• Dissolving material

with different solvents

• Varying spin

speeds

Dissolve & Spin Coat Thin Film Formed Solvent Anneal (3 hours) Put in dessicator

Step 1: OPV Film Production Step 2: Visible Spectroscopy Measurements

Experimental Methods

Dissolve & Spin Coat Thin Film Formed Solvent Anneal (3 hours) Put in dessicator

Step 1: OPV Film Production Step 2: Visible Spectroscopy Measurements

Experimental Methods

Photomultiplier tube

350 400 450 500 550 600 650 700 0.0 0.1 0.2 0.3 0.4 0.5 Absorbance Wavelength [nm]

500 rpm 1000 rpm 1500 rpm 2500 rpm 4000 rpm 6000 rpm

Film Absorbance vs. Spin Speed

P3HT Film Spin Casted from Chlorobenzene (CB), 10 mg/mL

350 400 450 500 550 600 650 700 0.0 0.1 0.2 0.3 0.4 0.5 Absorbance Wavelength [nm]

500 rpm 1000 rpm 1500 rpm 2500 rpm 4000 rpm 6000 rpm

• Faster spin

speed = thinner film

• Thinner film =

less absorbance

P3HT Film Spin Casted from Chlorobenzene (CB), 10 mg/mL

Film Absorbance vs. Spin Speed

Poly (3-Hexylthiophene) (P3HT) Film spin casted from Chlorobenzene (CB), 10 mg/mL

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 350 400 450 500 550 600 650 700

wavelength [nm] Absorbance 500 rpm 1000 rpm 1500 rpm 2500 rpm 4000 rpm 6000 rpm

• Faster spin

speed = thinner film

• Thinner film =

less absorbance

• Absorbance

decreases nonlinearly with spin speed as expected

1000 2000 3000 4000 5000 6000 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Absorbance Spin Speed [rpm]

P3HT Film Absorbance at 525 nm Wavelength

Film Absorbance vs. Spin Speed

500 550 600 650 0.0 0.2 0.4 0.6 0.8 1.0 Normalized Absorbance Wavelength [nm]

1000rpm 1500rpm 2500rpm 4000rpm 6000rpm

Normalized Absorbance vs. Spin Speed

Increasing Spin Speed

Faster spin speeds = more blue shift

P3HT Film Spin Casted from CB, 10 mg/mL

500 550 600 650 0.0 0.2 0.4 0.6 0.8 1.0 Normalized Absorbance Wavelength [nm]

1000rpm 1500rpm 2500rpm 4000rpm 6000rpm

Increasing Spin Speed

Faster spin speeds = more blue shift

• Faster spin

speed gives greater blue shift P3HT Film Spin Casted from CB, 10 mg/mL

Normalized Absorbance vs. Spin Speed

500 550 600 650 0.0 0.2 0.4 0.6 0.8 1.0 Normalized Absorbance Wavelength [nm]

1000rpm 1500rpm 2500rpm 4000rpm 6000rpm

Increasing Spin Speed

Faster spin speeds = more blue shift

• Faster spin

speed gives greater blue shift

• Blue shifts

indicate misalignment of polymers P3HT Film Spin Casted from CB, 10 mg/mL

Normalized Absorbance vs. Spin Speed

500 550 600 650 0.0 0.2 0.4 0.6 0.8 1.0 Normalized Absorbance Wavelength [nm]

1000rpm 1500rpm 2500rpm 4000rpm 6000rpm

Increasing Spin Speed

Faster spin speeds = more blue shift

• Faster spin

speed gives greater blue shift

• Blue shifts

indicate misalignment of polymers

• Misalignment of

polymers → poor charge transport P3HT Film Spin Casted from CB, 10 mg/mL

Normalized Absorbance vs. Spin Speed

350 400 450 500 550 600 650 700 0.0 0.5 1.0

Normalized Absorbance Wavelength [nm]

1:1 10:1 100:1 Pure P3HT

P3HT:PCBM Blend Films spin casted at 1000 rpm from CB

• The addition of PCBM

gives greater absorbance in the blue region

Effects of Adding PCBM

350 400 450 500 550 600 650 700 0.0 0.5 1.0

Normalized Absorbance Wavelength [nm]

1:1 10:1 100:1 Pure P3HT

More PCBM

P3HT:PCBM Blend Films spin casted at 1000 rpm from CB

• The addition of PCBM

gives greater absorbance in the blue region

• Adding more PCBM blue

shifts the entire spectrum

Effects of Adding PCBM

350 400 450 500 550 600 650 700 0.0 0.5 1.0

Normalized Absorbance Wavelength [nm]

1:1 10:1 100:1 Pure P3HT

More PCBM

P3HT:PCBM Blend Films spin casted at 1000 rpm from CB

• The addition of PCBM

gives greater absorbance in the blue region

• Adding more PCBM blue

shifts the entire spectrum

• Blue shift is caused by

PCBM molecules located between polymer chains, disrupting electronic order

Effects of Adding PCBM

350 400 450 500 550 600 650 700 0.0 0.5 1.0

Normalized Absorbance Wavelength [nm]

1:1 10:1 100:1 Pure P3HT

Effects of Adding PCBM

More PCBM

P3HT:PCBM Blend Films spin casted at 1000 rpm from CB

• The addition of PCBM

gives greater absorbance in the blue region

• Adding more PCBM blue

shifts the entire spectrum

• Blue shift is caused by

PCBM molecules located between polymer chains, disrupting electronic order

• This data, when

combined with photoluminescence data, will give us insight on the molecular ordering and excited states

400 450 500 550 600 650 700 750 800 850 900 0.0 0.2 0.4 0.6 0.8 1.0

Normalized PL or Abs Wavelength [nm]

P3HT Film Spin Casted from Chloroform, 10 mg/mL

• PL spectrum offers

complementary data to absorbance spectrum

Combined Absorbance and PL

Absorbance PL

400 450 500 550 600 650 700 750 800 850 900 0.0 0.2 0.4 0.6 0.8 1.0

Normalized PL or Abs Wavelength [nm]

P3HT Film Spin Casted from Chloroform, 10 mg/mL

• PL spectrum offers

complementary data to absorbance spectrum

• Height of 0-0 peak

relative to the central 0-1 peak indicates degree of

• rder in polymer

Combined Absorbance and PL

0-0 0-1 Absorbance PL

400 450 500 550 600 650 700 750 800 850 900 0.0 0.2 0.4 0.6 0.8 1.0

Normalized PL or Abs Wavelength [nm]

P3HT Film Spin Casted from Chloroform, 10 mg/mL

Combined Absorbance and PL

• PL spectrum offers

complementary data to absorbance spectrum

• Height of 0-0 peak

relative to the central 0-1 peak indicates degree of

• rder in polymer
• Comparison of

absorbance and PL spectra give surprising contradictory information about polymer ordering 0-0 0-1 Absorbance PL

1000 rpm 2000 rpm 5000 rpm

580 590 600 610 0.5 0.6

Normalized Absorbance Wavelength [nm]

660 680 0.5 0.6

Normalized PL Wavelength [nm] Increasing spin speed Increasing spin speed

• Increasing spin speed = blue shift
• Blue shift = shorter conjugation length

(disordered polymer)

• Increasing spin speed = lower 0-0/0-1

peak ratio

• Lower peak ratio = more ordered polymer

Combined Absorbance and PL

0-0

Summary

Summary

• Absorbance decreases nonlinearly with spin speed as

expected

• Faster spin speeds → thinner film → less absorbance

Summary

• Absorbance decreases nonlinearly with spin speed as

expected

• Faster spin speeds → thinner film → less absorbance
• Data trends seem to imply that increase in spin speed

always leads to spectral blue-shift

• Faster spin speeds → greater blue shift →

misalignment of polymers → poor charge transport

Summary

• Absorbance decreases nonlinearly with spin speed as

expected

• Faster spin speeds → thinner film → less absorbance
• Data trends seem to imply that increase in spin speed

always leads to spectral blue-shift

• Faster spin speeds → greater blue shift →

misalignment of polymers → poor charge transport

• Comparison of absorbance and PL spectra give surprising

contradictory information about polymer ordering

• Absorbance data indicate thinner films are more

disordered

• PL data indicate thinner films are more ordered

Future Plans

• Further research to understand contradictory results

between absorbance and PL data

• Use O2 plasma to treat substrate
• Can chemical modification of the solar cell substrate

affect alignment of the polymer?

• Polymer films will be used by other researchers in the lab

for advanced experiments

Acknowledgements

• INSET program – Jens, Nick, Arica
• The Gordon Lab
• Especially Michael J. Gordon and

Christopher Andrew Carach

Inlet slit Outlet slit

Monochromator

• Monochromator

splits the white light into individual wavelengths

Inlet slit Outlet slit

Monochromator Photomultiplier tube (PMT)

• Monochromator

splits the white light into individual wavelengths

• PMT

measures intensity of light at different wavelengths