Organic Solar CellsSupervisors:Dr. Ghazi

Dr. Izadifard

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presenter:Maryam Alidaie

Renewable Energy Consumption in the US Energy Supply, 2007

2http://www.eia.doe.gov/cneaf/solar.renewables/page/trends/highlight1.html

Different generations of solar cellsphotovoltaics

1st generationClassic Silicon

Poly crystal

Single crystal

2nd generationThin film

AmorphousSilicon

CdS

CI(G)S(e)

CdTe

3rd generationOrganic

Polymers

DSSE

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Organic Solar Cells

Organic or plastic solar cells use organic materials (carbon-compound based) mostly in the form of small molecules and polymers, to

convert solar energy into electric energy .

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Advantages

• The lower material consumption of OSCs is enabled by the much higher absorption of the organic materials at a given wavelength. Active layer thicknesses of a few hundred nanometers

• Less energy-demanding purification steps of the raw materials • The fast and easy R2R printing methods for large scale production

• Better environmental sustainability, their light weight, flexibility, and the possibility of transparency in different colors

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Disadvantages

o The hopping transport mechanism gives organic semiconductors a rather low mobility

o Large band gap and small absorption range which lead to low absorption efficiency of photons in the long wavelength region

o Low stability, oxidation, low efficiency

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History

• In the 1950s, the first investigations on the conductivity of organic materials were performed

• in the 1970s, OSCs with efficiencies of 10−5% were produced • In the mid-1980s, Tang could increase the efficiency to around 1%• In the mid-1990s, the concept of blend solar cells was developed • In Bulk heterojunction architecture efficiency of 8.3% on a 1 cm2

single-junction device was demonstrated by the end of 2010

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Efficiency evolution of OSCs

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Materials for OSCs

• Active Materials for OSCs : {MEH-PPV:C60 } {MDMO-PPV:PCBM} {P3HT-PCBM} {CuPc:C60} {ZnPc:C60}• Interfacial Materials PEDOT:PSS (hole-selective electrode )• Electrode Materials ITO, Ca, Al, Ag, or Au• Solvent (for Solution Processing) Chlorobenzene, Toluene

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Chemical Structure of Organic solar cell Donor and Acceptor (Active)Materials

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acceptor donor

C60 MDMO-PPV

PCBM P3HT

CuPc

MEH-PPV

*

*

O

O

MDMO-PPV

OMe

O

PCBM

*S

*

P3HT

CuPc

C60

MEH-PPV

Device architecture

ITO glass

Top electrode

Active layer

Bilayer Bulk heterojunction

The difference of these architectures lays in the charge

generation mechanism

Single layer

Organic or polymer single-layer PVs

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Disadvantage

Single-layer PVs

•Single crystalline pentaceneiodine-doped (bromine-doped)

About 7 mm2

AM 1.5, 100mW/cm2

η=1.9% (2.4%)955( 970 )mV = Voc

4.6 mA cm-2 (5.3 mA cm-2)= Jsc

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device performance increases by more than five orders of magnitude

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BILAYER PVS

Bilayer PVs

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Normal bilayer Inverted bilayer

Bulk heterojunction (BHJ) PVs

Bulk heterojunction or blend Solar where active layer consists of a mixture of donor and acceptor materials .

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Fabrication sequence for ITO-free bulk-heterojunction solar cells

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Heterojunction solar cells with a spray-coated PEDOT:PSS anode and a spray-coated P3HT:PCBM active layer

Bulk heterojunction (BHJ) PVs

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Working principle of BHJ device

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1 .Incoming photons are absorbed ⇒Creation of excitons on the Donor/

Acceptor

2 .Exciton is separated at the donor/ acceptor interface Creation of charge ⇒carriers

3 .Charge carriers within drift distance reach electrodes Creation of short circuit ⇒current ISC

1 .The “photodoping” leads to splitting of Fermi levels Creation of open circuit ⇒voltage VOC

2 .Charge transport properties, modulegeometry Fill factor FF⇒

*

*

O

O

OMe

O

MDMO-PPV PCBM

Donor/Acceptor composite solution

DA

Voc = 0.82 V

Jsc = 5.25 mA/cm2

FF = 0.61

AM1.5G = 2.5 % (under 80 mW/cm2)

<S. E. Shaheen, et al. 1998 >

glass

ITO

LiF

PEDOT:PSS

Active layer

Metal electrode

Polymer/PCBM interpenetrating system

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Tandem solar cells

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first tandem organic solar cell realizedby Hiramoto et al (1990)

• Based on evaporated small molecules• 50 nm of metal-free phthalocyanine (H2Pc)• 70 nm perylene tetracarboxylic derivative (Me–PTC)• In order to make ohmic contact between the two sub-cells, an

ultra-thin (2 nm) Au interstitiallayer was evaporated• 2 nm thick Au layer

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VOC = 0.78 V about twice the VOC of a single cell )0.44 V(

2 nm thick Au layerEffective recombination center

Tandem solar cells Yakimov and Forrest(In 2002)

• (CuPc) as a donor, (PTCBI) as acceptor• An ultrathin (z5A° ) discontinuous layer of Ag clusters served

as the charge recombination sites.• (η) of the two and three HJ cells under one sun, η =2.5% and• 2.3%, with VOC = 0.93 and 1.2 V (twice that of a comparable

single junction cell)

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Significant improvement in efficiency by stacking two bulk-heterojunctions, J. Xue(2004)

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They report an efficiency of up to 5.7%, )about 24% more efficient than the single CuPc/C60 devices(

Thin layers of PTCBI and bathocuproine )BCP( were

employed as ‘‘exciton blocking layer’’

Tandem organic solar cell realized by Maennig et al based on multiple stacked p–i–n structures (2004)

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• Active region is sandwiched between two wide band gap layers.

• p-type)p-doped MeO–TPD( and the n-type C60 layers were the best choices.

• efficiency close to 2% in single cells.

• higher power efficiency of 2.4% for tandem P-i-n cells

Origin of open-circuit voltage (Voc)

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Which is the Voc?

(Is it in the electrodes? (Voc

(Is it in the bulk-heterojunction? )Voc

The specific case of organic solar cells

• It is shown experimentally that 0.3 eV is a minimum value below which the charge transfer may not occur.

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Energy-level diagram showing the HOMO and LUMO energies of each of the component

materials.

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Production Methods

Spin coating of thin layers Dip coating Doctor blade Spray coating Inkjet printing R2R production

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Future Generation - Printable Cells

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References

1. Organic solar cells, materials and device physics(2013) Springer (Ebook)2. Plastic Solar Cells, L Sims, Comprehensive Renewable Energy, Volume 1 (2012)3. Angew. Chem. Int. Ed. (2012) 20204. Seok-In Na et al, Solar Energy Materials & Solar Cells 94 (2010) 13335. Tayebeh Ameri et al, Energy Environ. Sci, 2(2009)3476. Jin Young Kim et al, Science 317 (2007) 2227. Chih-Wei Chu , Appl. Phys. Lett , 86(2005) 2435068. A. Yakimov and S. R. Forrest, Appl. Phys. Lett. 80 (2002), 16679. J. H. Schoen, Nature 403(2000)40810. S. E. Shaheen, et al. Journal of Applied Physics, 84 (1998) 2324

11. c. W. Tang, Appl. Phys. Lett, 48 (1986) 183 12. www.pveducation.org13. http://www.eia.doe.gov/cneaf/solar.renewables/page/trends/highlight1.html

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