Self Assembly in Photovoltaic Devices

Zaahir Salam

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

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.

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.

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.

n-type semiconductor

p-type semiconductor

+ + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - -

Physics of Photovoltaic Generation

Depletion Zone

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)

Published In 1995

Phenyl C61-Butyric acid methyl ester(PC61BM)

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

• 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.

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.

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.

• 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.

• 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.

• 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.

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

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

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

TiO2 Coated ZnO Arrays

Aligned ZnO nano-rods in a hexagonal matrix on a sapphire substrate.

Aligned ZnO nano-rods coated with 100 nm of TiO2 at 100°C.

SELF ASSEMBLY!

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*,†

THANK YOU FOR YOUR KIND ATTENTION AND PATIENCE

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