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 exposolar.org Mentor: Chris Carach Faculty Advisor: Dr. Mike Gordon Funding Sources: National Science Foundation

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 U.S. Energy Information Administration – High production costs When will fossil fuels reserves be depleted? – Some contain toxic elements Crude oil ~ 35 years (lead, cadmium) 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 U.S. Energy Information Administration – High production costs When will fossil fuels reserves be depleted? – Some contain toxic elements (lead, Crude oil ~ 35 years cadmium) Gas ~ 37 years • Organic Photovoltaics Coal ~ 107 years – Produced cheaply (roll-to-roll processing) Shafiee and Topal – Environmentally friendly Energy Policy , 37 , 181 (2009)

Research Goals • Understand how the processing of the solar cell materials affects optical properties and morphology Phenyl-C61-Butyric Acid Methyl Ester Poly-3-Hexylthiophene

Research Goals • Understand how the processing of the solar cell materials affects optical properties and morphology Photoluminescence and Absorption Spectra – Absorption of light • More absorption = better solar cell I o Absorption I t

Research Goals • Understand how the processing of the solar cell materials affects optical properties and morphology: – Absorption of light • More absorption = better solar cell – Alignment of the polymer chains PL • Better alignment = better charge transport

Research Goals • Understand how the processing of the solar cell materials affects optical 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

Experimental Methods Step 1: OPV Film Production

Experimental Methods Step 1: OPV Film Production Dissolve & Spin Coat Thin Film Formed Solvent Anneal Put in dessicator (3 hours) • Dissolving material • Varying spin with different speeds solvents

Experimental Methods Step 1: OPV Film Production Thin Film Formed Dissolve & Spin Coat Solvent Anneal Put in dessicator (3 hours) Step 2: Visible Spectroscopy Measurements

Experimental Methods Step 1: OPV Film Production Dissolve & Spin Coat Thin Film Formed Solvent Anneal Put in dessicator (3 hours) Step 2: Visible Spectroscopy Measurements Photomultiplier tube

Film Absorbance vs. Spin Speed P3HT Film Spin Casted from Chlorobenzene (CB), 10 mg/mL 0.5 500 rpm 0.4 1000 rpm 1500 rpm 2500 rpm 0.3 Absorbance 4000 rpm 6000 rpm 0.2 0.1 0.0 350 400 450 500 550 600 650 700 Wavelength [nm]

Film Absorbance vs. Spin Speed P3HT Film Spin Casted from Chlorobenzene (CB), 10 mg/mL • Faster spin 0.5 speed = thinner film 500 rpm 0.4 1000 rpm 1500 rpm •Thinner film = 2500 rpm 0.3 Absorbance less absorbance 4000 rpm 6000 rpm 0.2 0.1 0.0 350 400 450 500 550 600 650 700 Wavelength [nm]

Film Absorbance vs. Spin Speed Poly (3-Hexylthiophene) (P3HT) Film spin casted from Chlorobenzene (CB), 10 mg/mL 0.5 500 rpm 0.45 1000 rpm 1500 rpm 0.4 2500 rpm 0.35 P3HT Film Absorbance at 525 nm Wavelength 4000 rpm Absorbance 0.3 6000 rpm 0.25 0.50 0.2 0.15 0.1 0.05 0.45 0 350 400 450 500 550 600 650 700 wavelength [nm] • Faster spin 0.40 speed = thinner Absorbance film 0.35 • Thinner film = 0.30 less absorbance 0.25 • Absorbance decreases 0.20 nonlinearly with spin speed as 0 1000 2000 3000 4000 5000 6000 expected Spin Speed [rpm]

Normalized Absorbance vs. Spin Speed P3HT Film Spin Casted from CB, 10 mg/mL 1.0 1000rpm 1500rpm 0.8 2500rpm Normalized Absorbance 4000rpm 6000rpm 0.6 Increasing Spin Speed 0.4 0.2 Faster spin speeds = more blue shift 0.0 500 550 600 650 Wavelength [nm]

Normalized Absorbance vs. Spin Speed P3HT Film Spin Casted from CB, 10 mg/mL 1.0 1000rpm •Faster spin 1500rpm speed gives 0.8 2500rpm greater blue shift Normalized Absorbance 4000rpm 6000rpm 0.6 Increasing Spin Speed 0.4 0.2 Faster spin speeds = more blue shift 0.0 500 550 600 650 Wavelength [nm]

Normalized Absorbance vs. Spin Speed P3HT Film Spin Casted from CB, 10 mg/mL 1.0 1000rpm •Faster spin 1500rpm speed gives 0.8 2500rpm greater blue shift Normalized Absorbance 4000rpm 6000rpm •Blue shifts 0.6 Increasing Spin Speed indicate misalignment of polymers 0.4 0.2 Faster spin speeds = more blue shift 0.0 500 550 600 650 Wavelength [nm]

Normalized Absorbance vs. Spin Speed P3HT Film Spin Casted from CB, 10 mg/mL 1.0 1000rpm •Faster spin 1500rpm speed gives 0.8 2500rpm greater blue shift Normalized Absorbance 4000rpm 6000rpm •Blue shifts 0.6 Increasing Spin Speed indicate misalignment of polymers 0.4 •Misalignment of polymers → poor 0.2 charge transport Faster spin speeds = more blue shift 0.0 500 550 600 650 Wavelength [nm]

Effects of Adding PCBM P3HT:PCBM Blend Films spin casted at 1000 rpm from CB •The addition of PCBM 1.0 gives greater absorbance 1:1 in the blue region 10:1 100:1 Normalized Absorbance Pure P3HT 0.5 0.0 350 400 450 500 550 600 650 700 Wavelength [nm]

Effects of Adding PCBM P3HT:PCBM Blend Films spin casted at 1000 rpm from CB •The addition of PCBM 1.0 gives greater absorbance 1:1 in the blue region 10:1 100:1 •Adding more PCBM blue Normalized Absorbance Pure P3HT shifts the entire spectrum 0.5 More PCBM 0.0 350 400 450 500 550 600 650 700 Wavelength [nm]

Effects of Adding PCBM P3HT:PCBM Blend Films spin casted at 1000 rpm from CB •The addition of PCBM 1.0 gives greater absorbance 1:1 in the blue region 10:1 100:1 •Adding more PCBM blue Normalized Absorbance Pure P3HT shifts the entire spectrum •Blue shift is caused by 0.5 PCBM molecules located between polymer chains, More PCBM disrupting electronic order 0.0 350 400 450 500 550 600 650 700 Wavelength [nm]

Effects of Adding PCBM P3HT:PCBM Blend Films spin casted at 1000 rpm from CB •The addition of PCBM 1.0 gives greater absorbance 1:1 in the blue region 10:1 100:1 •Adding more PCBM blue Normalized Absorbance Pure P3HT shifts the entire spectrum •Blue shift is caused by 0.5 PCBM molecules located between polymer chains, More PCBM disrupting electronic order • This data, when combined with photoluminescence data, 0.0 will give us insight on the 350 400 450 500 550 600 650 700 molecular ordering and Wavelength [nm] excited states

Combined Absorbance and PL P3HT Film Spin Casted from Chloroform, 10 mg/mL 1.0 • PL spectrum offers complementary data to absorbance spectrum 0.8 Normalized PL or Abs 0.6 0.4 Absorbance PL 0.2 0.0 400 450 500 550 600 650 700 750 800 850 900 Wavelength [nm]

Combined Absorbance and PL P3HT Film Spin Casted from Chloroform, 10 mg/mL 1.0 0-1 • PL spectrum offers complementary data to absorbance spectrum 0.8 0-0 Normalized PL or Abs • Height of 0-0 peak relative to the central 0-1 0.6 peak indicates degree of order in polymer 0.4 Absorbance PL 0.2 0.0 400 450 500 550 600 650 700 750 800 850 900 Wavelength [nm]

Combined Absorbance and PL P3HT Film Spin Casted from Chloroform, 10 mg/mL 1.0 0-1 • PL spectrum offers complementary data to absorbance spectrum 0.8 0-0 Normalized PL or Abs • Height of 0-0 peak relative to the central 0-1 0.6 peak indicates degree of order in polymer 0.4 • Comparison of Absorbance PL absorbance and PL spectra give surprising 0.2 contradictory information about polymer ordering 0.0 400 450 500 550 600 650 700 750 800 850 900 Wavelength [nm]

Combined Absorbance and PL 1000 rpm 0-0 2000 rpm 0.6 5000 rpm Normalized Absorbance 0.6 Normalized PL 0.5 Increasing spin speed 0.5 Increasing spin speed 580 590 600 610 660 680 Wavelength [nm] Wavelength [nm] • Increasing spin speed = blue shift • Increasing spin speed = lower 0-0/0-1 peak ratio •Blue shift = shorter conjugation length • Lower peak ratio = more ordered polymer (disordered polymer)