1. Supervisors: Dr. Ghazi Dr. Izadifard
Organic Solar Cells
Supervisors:
Dr. Ghazi
Dr. Izadifard
presenter:
Maryam Alidaie

2. Renewable Energy Consumption in the US Energy Supply, 2007

3. Different generations of solar cells
photovoltaics
1st generation
Classic Silicon
Poly crystal
Single crystal
2nd generation
Thin film
Amorphous
Silicon
CdS
CI(G)S(e)
CdTe
3rd generation
Organic
small molecule
Polymers
DSSE

4. 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.

5. 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

6. Disadvantages
The hopping transport mechanism gives organic semiconductors a rather low mobility
Large band gap and small absorption range which lead to low absorption efficiency of photons in the long wavelength region
Low stability, oxidation, low efficiency

7. History in the 1970s, OSCs with efficiencies of 10−5% were produced
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

8. Efficiency evolution of OSCs

9. 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

10. Chemical Structure of Organic solar cell Donor and Acceptor (Active)Materials
MDMO-PPV
PCBM
P3HT
CuPc
MEH-PPV
PCBM
MDMO-PPV
C60
P3HT
CuPc
MEH-PPV

11. Device architecture
Top electrode
The difference of these architectures lays in the charge generation mechanism
Active layer
ITO glass
Single layer
Bilayer
Bulk heterojunction

12. Organic or polymer single-layer PVs
Disadvantage

13. device performance increases by more than five orders of magnitude
Single-layer PVs
Single crystalline pentacene
iodine-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
device performance increases by more than five orders of magnitude

14. bilayer PVs

15. Bilayer PVs
Normal bilayer
Inverted bilayer

16. Bulk heterojunction (BHJ) PVs
Bulk heterojunction or blend Solar where active layer consists of a mixture of donor and acceptor materials.

17. Fabrication sequence for ITO-free bulk-heterojunction solar cells
Heterojunction solar cells with a spray-coated PEDOT:PSS anode and a spray-coated P3HT:PCBM active layer

18. Bulk heterojunction (BHJ) PVs

19. Working principle of BHJ device
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, module
geometry ⇒ Fill factor FF

20. Polymer/PCBM interpenetrating system
Voc = 0.82 V
Jsc = 5.25 mA/cm2
FF = 0.61
 AM1.5G = 2.5 % (under 80 mW/cm2) O M e
MDMO-PPV
PCBM
< S. E. Shaheen, et al > A D
Metal electrode
LiF
Active layer
PEDOT:PSS
ITO
glass
Donor/Acceptor composite solution

21. Tandem solar cells

22. first tandem organic solar cell realized by 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
2 nm thick Au layer
Effective recombination center
VOC = 0.78 V
about twice the VOC of a single cell (0.44 V)

23. 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)

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

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

26. Origin of open-circuit voltage (Voc)
Which is the Voc?
(Is it in the electrodes? (Voc
(Is it in the bulk-heterojunction? (Voc

27. 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.

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

29. Production Methods Spin coating of thin layers Dip coating
Doctor blade
Spray coating
Inkjet printing
R2R production

30. Future Generation - Printable Cells

31. References
Organic solar cells, materials and device physics(2013) Springer (Ebook)
Plastic Solar Cells, L Sims, Comprehensive Renewable Energy, Volume 1 (2012)
Angew. Chem. Int. Ed. (2012) 2020
Seok-In Na et al, Solar Energy Materials & Solar Cells 94 (2010) 1333
Tayebeh Ameri et al, Energy Environ. Sci, 2(2009)347
Jin Young Kim et al, Science 317 (2007) 222
Chih-Wei Chu , Appl. Phys. Lett , 86(2005)
A. Yakimov and S. R. Forrest, Appl. Phys. Lett. 80 (2002), 1667
J. H. Schoen, Nature 403(2000)408
S. E. Shaheen, et al. Journal of Applied Physics, 84 (1998) 2324
c. W. Tang, Appl. Phys. Lett, 48 (1986) 183