Solar Photovoltaics & Energy Systems...7 }Low cost processing }Roll-to-roll compatible }Solution...

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Solar Photovoltaics & Energy Systems Parts 8. Dye sensitized solar cells ChE-600 Kevin Sivula, Spring 2012

Averaged Solar Radiation 1990-2004

Assuming 8% energy conversion efficiency

Thin Film performance overview

Installed capacity of photovoltaics

http://www.ren21.net/Portals/97/documents/GSR/REN21_GSR2011.pdf

x-Si approaches grid parity

Without a significant paradigm shift in fabrication

“Generations” of solar cells

A new paradigm for solar energy conversion

} Low cost processing } Roll-to-roll compatible } Solution processing } Atmospheric pressure } Avoid high temperatures

Paint Cost = $1/m2

} High conversion efficiency } High stability

} Low to medium purity materials } Solar light absorption } Transport of electric charge

Natural photosynthesis

Light harvesting

cryptoxanthin

Molecular orbitals review

Metal-organic dyes and pigments

Excitation of a molecular absorber

Electron energy

Excited state (S*)

Ground state (S°)

Light energy (hν)

Dye molecule

Chemical Structure of N3 Dye

Conditions for molecular absorption: 1. hν = S* - So

2. The transition dipole

moment is not zero

for a transition between an initial state, n, and a final state, m

Excitation of a molecular absorber

Electron energy

Excited state (S*)

Ground state (S°)

Light energy (hν)

Dye molecule

S° + hν → S* (excitation) S*→S° (deactivation) 50 ns Chemical Structure of N3 Dye Ground state (S°)

Excited state (S*)

Capturing the excited state with a DSC

1. Light absorption 2. Injection to

semiconductor

S°/S+

Dye Electrolyte

Ox Red

Cathode

2 -1.0

Wide band-gap semiconductor

Physics of electron transfer

Ultrafast electron injection

Ground state (S°)

Excited state (S*)

Capturing the excited state with a DSC

1. Light absorption 2. Injection to

semiconductor 3. Percolation 4. Regeneration of

oxidized species 5. Regeneration of

oxidized dye

S°/S+

Dye Electrolyte

Ox Red

Maximum Voltage

Cathode

External circuit

The DSC vs. Conventional pn junction PV

Electrolyte

Cathode

n-type Silicon

p-type Silicon

• Charge carriers (excited electrons) are produced throughout the semiconductor • Semiconductor considerations:

• Precise doping • high purity • high crystalinity

• Light absorption and charge transport are decoupled • Relaxed constraints on individual components (each can be separately tuned) • Only monolayer of dye on TiO2

Device characterization metrics

IPCE(λ) = = habs Fcg hcoll

hab: light harvesting efficiency

Fcg: quantum yield of charge carrier generation

hcoll = efficiency of charge carrier collection

Electrons out

Photons in

PCE or ηPCE = = JSC : Short circuit current density

VOC : Open circuit voltage

FF: Fill factor

Max. power out

Power in

JSC VOC FF

Ilight/A

max (J·V) JSC VOC

22 Solar intensity mW cm-2

Single crystal silicon cell

Dye sensitized cell

Dye sensitized solar cells outperform silicon at lower light levels

Higher open circuit voltage at low light intensity gives dye cell better performance in diffuse daylight

History of the Dye Sensitized solar cell

mesoscopic photoelectrochemial

100 nm

highly efficient sensitization of

TiO2 nano-crystals

B.O’Regan and M. Grätzel, Nature 1991,

353, 737

1985 1988 1991 2006 2010

Mesoscopic structure is critical

Electrolyte

Cathode

IPCE = electrons out

photons incident

Single crystal TiO2

Nanocrystalline anatase TiO2

Dye monolayer on Single crystal TiO2

Dye Sensitized Mesoporous anatase TiO2

( <101> anatase)

Benefits of the nanostructure

• Surface area • Photoinduced conductivity • Charge carrier screening

100 nm IPCE =

electrons out photons incident

Single crystal TiO2

H.G. Agrell, G. Boschloo, A. Hagfeldt J. Phys. Chem. B 2004, 108, 12388

photons incident

Single crystal TiO2

Electrons in TiO2 Surrounding electrolyte

Electron diffusion

No space-charge Layer at TiO2 - electrolyte interface

photons incident

Single crystal TiO2

Redox couple selection

S°/S+

Dye Electrolyte

Ox Red

External circuit

20 nm TiO2 particles +

400 nm TiO2 particles

Optical Engineering with Advanced Nanostructures

G. Rothenberger et al. Solar Energy Materials & Solar Cells 58 (1999) 321 Hore S, Vetter C, Kern R, et al. Solar Energy Materials & Solar Cells 90 (2006) 1176

20 nm TiO2 particles +

Optical Engineering with Advanced Nanostructures

Engineering the dye

M.K. Nazeeruddin et al., J. Am. Chem.Soc. 123, 1613, (2001)

N749 tri(cyanato)-2.22-terpyridyl-4,44-tricarboxylate)Ru(II)

N3 cis-Ru(SCN)2L2

(L = 2,2-bipyridyl-4,4-dicarboxylate)

3- [(C4H9)N]3+

Record high conversion efficiencies

Need to increase band width of light absorption

} Difficult to construct dye with pan-chromatic light absorption } Organic dyes } Porphyrin-based dyes

Yum et. al. J. AM. CHEM. SOC. 2007, 129, 10320-10321

Cid et. al. Angew. Chem. Int. Ed. 2007, 46, 8358 –8362

Altering the colors absorbed and transmitted

Device Stability

The sensitizer has to sustain 100 million cycles during 20 years of outdoor cell operation

To reach 100 million turnovers branching ratios of kInj/k1 and kreg/k2 > 108 are required

Device Stability

The sensitizer has to sustain 100 million cycles during 20 years of outdoor cell operation

To reach 100 million turnovers branching ratios of kInj/k1 and kreg/k2 > 108 are required

Light soaking at 2.5 suns (2.5kW/m2)

DSC masterplates

Requirements for outdoor use according to international PV standards applied to single crystal silicon but so far not to thin film PV cells Light soaking (full sun 55-60 C): 1000 hours Heat stress at 85 C: 1000 h Hot humidity test (85%/85C) and temperature cycling

Device Stability

The C101 sensitizer maintains outstanding stability at efficiency levels over 9 percent under light soaking at 60oC using a low- volatility electrolyte

The present status of dye sensitized solar cells

• Power conversion efficiency measured under AM 1.5 sunlight: laboratory cells 12 %, modules 9.5 % (Sony), tandem cells 16%

• stability > 20 years outdoors (DYESOL)

• energy pay back time: < 1 year (3GSolar and ECN, life cycle analysis)

• ease of building integration • transparency and multicolor option (for power window application) • Flexibility • light weight • low production cost • feedstock availability to reach terawatt scale • short energy pay back time (< 1 year) • enhanced performance under real outdoor conditions • bifacial cells capture light from all angles • tandem cell configurations boost efficiency over 15 % • outperforms competitors for indoor applications • Industrial development: roll to roll mass production and commercial sales of light

weight flexible cells started in Cardiff Wales by G24 Innovation (www.g24i.com.)

The G24I plant in Cardiff has started production on June 21 (solstice),2007

The first G24I product is a light weight flexible power supply for portable electronics

The beauty of a dye-sensitized Walkman

Solar Powered Solar Panel Sun Glasses The SIG, or “Self-Energy Converting Sunglasses” are quite simple. The lenses of the glasses have dye solar cells, collecting energy and making it able to power your small devices through the power jack at the back of the frame. “Infinite Energy: SIG”

mesoscopic photoelectrochemial

highly efficient sensitization of

TiO2 nano-crystals

B.O’Regan and M. Grätzel, Nature 1991,

353, 737

Mass production

1985 1988 1991 2009 2005

Scale up to modules

tomorrow

Solar Photovoltaics & Energy Systems...7 }Low cost processing }Roll-to-roll compatible }Solution...

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