Self-assembly techniques can be used to construct nanostructures for photovoltaic devices in a cheaper and faster way compared to traditional fabrication methods. The document discusses how self-assembly of porphyrin and fullerene molecules on metal oxide electrodes leads to the formation of clusters that absorb light effectively across the visible spectrum. It also describes how coating aligned ZnO nanorods with TiO2 using atomic layer deposition creates a two-dimensional photonic crystal for enhanced light harvesting in dye-sensitized solar cells. Overall, the document outlines the potential of self-assembly methods to organize functional organic and inorganic materials into nanostructures that improve the performance of organic and perovskite photovoltaics.

1. Self Assembly in Photovoltaic Devices
Zaahir Salam

2. Contents
• What is Self Assembly
• Why We need Self Assembly
• Top 10 problems ,humanity will face in coming 50 Years
• What are Photovoltaic and How they work
• Self-Assembly of Selective Interfaces in Organic Photovoltaics
Porphyrin-and Fullerene-Based Molecular Photovoltaic
Devices
• Relationship in Dye sensitized Solar cells
• References

3. What’s Self-assembly
Self-assembly is a
method of constructing
nanoscale device and
machines.
The technique works by
simulating the way
biological systems build
molecules, viruses, cells,
plants, and animals.
The technology is
largely unexploited.

4. Why We Need Self-Assembly?
• For pursuing cheaper and faster computers,
chipmakers have to shrink their chips from
microns to nanometers along with Moore’s law.
• The existing approaches tend to be high-cost for
fabricating nano-scale devices.
• It helps us in organizing functional molecules on
substrates which help to create devices like PV’s.

9. What are Photovoltaic's?
• First used in about 1890, the word has two parts:
–photo, derived from the Greek word for light,
–volt, relating to electricity pioneer Alessandro
Volta.
• Photovoltaics could literally be translated as light-
electricity.
• Photovoltaics use semiconductor materials to convert
sunlight into electricity.

10. Physics of Photovoltaic Generation
n-type
semiconductor
+ + + + + + + + + + + + + + + Depletion Zone
- - - - - - - - - - - - - - - - - -
p-type
semiconductor

11. Self-Assembly of Selective Interfaces in Organic
Photovoltaics
• The photoactive layer of polymer-based organic photovoltaic
(OPV) devices is typically a bulk heterojunction (BHJ), in
which a polymer electron donor and fullerene electron
acceptor are cast from a common solution to form a mixed
layer.
Poly(phenylene Vinylene)
Phenyl C61-Butyric
acid methyl
ester(PC61BM)
Published In 1995

12. • The components form
an interpenetrating,
phase-separated
network that provides
a large interfacial area
for charge separation
and continuous
pathways for charge
transport.

13. • The most studied donor-acceptor system is poly(3-
hexylthiophene) (P3HT) and (6,6)-phenyl-C 61 -butyric acid
methyl ester (PCBM).
• Nanoscale morphology of the BHJ plays a critical role in the
efficiency of OPV devices.
• As a result, much of the subsequent research on P3HT:PCBM
BHJs focused on how processing conditions such as casting
solvent, deposition method, annealing method, and drying
rate could be used to tune the morphology to maximize
efficiency.

14. Solar Power Conversion Efficiency(PCE)
 Product of 3 electrical properties: Isc, Voc, and Fill Factor(FF).
 The Isc, or the device photocurrent at zero bias, is the
product of the number of photons absorbed and the
efficiency of free charge carrier generation and collection.
 The Fill Factor is, in part, a function of the efficiency of
charge migration to the electrodes.
 Voc is difference between HOMO of Donor and LUMO of
Acceptor which is reduced from the value predicted
approximately by 0.3 V, because of the energies associated
with the molecular distortions involved in carrier
formation.

15. 2004,14,No. 6, June
The construction of molecular photovoltaic devices
where the porphyrins and fullerenes are employed
as building blocks are organized into Artificial
Photosynthetic System by Self assembly process.

16. • Composites of donor and acceptor moieties , in the
form of clusters have been assembled as a 3-D on
conducting surface for attaining efficient
photocurrent generation.
• Tailoring of these electron-donor and acceptor
molecular assemblies can give us better
photovoltaic devices with better efficiency.

17. • Porphyrins and Fullerenes are know to form complex in both
solution and solid state.
• Therefore these composites in mixture of polar and non-
polar solvents are expected to assemble into larger clusters,
which can be further associated onto a nanostructured SnO2
electrode using electrophoretic deposition technique.

18. • When a Conc. Solution of C60 or H2P-ref[5,15-bis(3,5-di-tert-
butylphenyl) porphyrin] in toulene is mixed with acetonitrile
by a fast injection method, the molecules aggregate and
form stable clusters.
• The Absorption Spectrum of H2P-ref and C60 in neat toulene
were compared with the absorption spectrum of [(H2P-
ref+C60)m ] clusters in acetonitrile/toulene (3:1, v/v).
• Composite cluster of H2P-ref and C60 are better light
absorbers than single component clusters of H2P-ref or C60
since they absorb throughout the visible part of the solar
spectrum.
• The absorption spectra of ITO/SnO2 / (H2P-ref+C60)m
electrodes were measured at different precursor
concentrations of H2P and C60.

19. Construction of BHJ on nanostructured SnO2 electrode using EPD has encouraged
quaternary self organization of Poryphrin and C60 with gold Nanoparticles on SnO2
electrodes.

22. The main problem was that a monolayer of dye molecules on a flat surface can only
absorb up to 1 % of the incident light. Introduction of nanoporous TiO2 electrodes with
a roughness factor of ca. 1000 dramatically increased the light harvesting efficiency

25. Using ALD of TiO2 to create novel
2D Photonic Crystals.
X. D. Wang, E. Graugnard, J. S. King,
C. J. Summers, and Z. L. Wang

26. TiO2 Coated ZnO Arrays
Aligned ZnO nano-rods in a hexagonal Aligned ZnO nano-rods coated with 100
matrix on a sapphire substrate. nm of TiO2 at 100°C.
SELF ASSEMBLY!

27. References
 PHOTONIC CRYSTALS @ GEORGIA TECH E. Graugnard, J. S. King, Curtis Neff, Davy Gaillot,
Tsuyoshi Yamashita, D. Heineman, and C. J. Summers School of Materials Science and
Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
 “Plastic” Solar Cells: Self-Assembly of Bulk Heterojunction Nanomaterials by Spontaneous
Phase Separation JEFFREY PEET, ALAN J. HEEGER,* AND GUILLERMO C. BAZAN* Center for
Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara,
California 93106 RECEIVED ON FEBRUARY 27, 2009.
 Hierarchical self-assembly of all-organic photovoltaic devicesChih-Hao Huang,a Nathan D.
McClenaghan,a Alexander Kuhn,b Georges Bravicc and Dario M. Bassania,*
 Using Self-Organization To Control Morphology in Molecular Photovoltaics Seok Ju
Kang,†,# Seokhoon Ahn,†,# Jong Bok Kim,‡ Christine Schenck,† Anna M. Hiszpanski,‡
Seokjoon Oh,† Theanne Schiros,§ Yueh-Lin Loo,‡ and Colin Nuckolls*,†

28. THANK YOU FOR YOUR KIND
ATTENTION AND PATIENCE
Questions?