Organic Solar Cells

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Organic Solar Cells

• Elizabeth Thomsen

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Organic Semiconductors
Organic
Semi Conductor
Artists impression!
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Organic Semiconductors

• Combine the virtues of plastics with those of
  semiconductors
• High optical absorption coefficients
• Properties tuned with flexible synthesis
• Low cost fabrication

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Organic Solar Cells

• Potential for medium efficiency, very low cost
  solar cells

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Organic Solar Cells
Charge extraction of carriers
Absorption of photons to form excitons
Charge separation of excitons
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Conjugated materials

• Polymers generally insulating
• Alternating single and double bonds (conjugated)
• p electrons able to delocalise into clouds above
  and below the chain
• Bandgap suitable for absorption of sunlight

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Active Layer Materials
Electron transporter
Hole transporter
Conjugated polymer
Fullerenes
Conjugated dendrimer/ small molecule
Nanocrystals
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Conjugated material nanocrystal composites

• Typically nanocrystals synthesised separately to
  polymer, then mixed
• Disadvantages
• Nanocrystal surfactant inhibits charge transfer
• Co-solvents required for mixing can adversely
  affect nanocrystal solubility and polymer chain
  orientation
• One-pot synthesis of conjugated polymer
  nanocrystal composite developed by Watt et al.
• Extended this synthesis to a conjugated oligomer
  and a dendrimer

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Conjugated small molecule nanocrystal composite
Oligomer
Dendrimer
PbS
CdS
Sulphur flakes in toluene
Toluene DMSO
Oligomer CdS in chloro-benzene
OligomerCadmium acetate
110C
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Oligomer CdS
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CdS Rods
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Final thoughts

• Grew PbS and CdS nanocrystals in oligomer, PbS
  nanocrystals in dendrimer
• Highly likely the synthesis can be generalised to
  a variety of conjugated soluble small molecule
  nanocrystal systems
• Combination of materials extends the absorption
  spectrum
• Direct interaction between the small molecule and
  the nanocrystal is likely to enable efficient
  charge separation
• Shape control of nanoparticles may improve charge
  transfer through the device

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Acknowledgements

• Alexandros Stravinadis
• Andrew Watt

Thankyou for listening!