organic solar cells elizabeth thomsen. organic semiconductors artist’s impression! semi conductor...

Organic Solar Cells

Elizabeth Thomsen

Organic Semiconductors

Artist’s impression!

Semi Conductor

Organic

Organic Semiconductors

Combine the virtues of plastics with those of semiconductors

High optical absorption coefficients

Properties tuned with flexible synthesis

Low cost fabrication

Organic Solar Cells

Potential for medium efficiency, very low cost solar cells

Organic Solar Cells

Absorption of photons to form excitons

Charge separation of excitons

Charge extraction of carriers

Conjugated materials Polymers generally

insulating Alternating single and

double bonds (conjugated) π electrons able to

delocalise into clouds above and below the chain

Bandgap suitable for absorption of sunlight

Active Layer Materials

Hole transporter

Electron transporter

Conjugated polymer

Conjugated dendrimer/

small molecule

Fullerenes

Nanocrystals

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

Conjugated small molecule: nanocrystal composite

OligomerCadmium acetate

Toluene DMSO

110°C

Sulphur flakes in toluene Oligomer:

CdS in chloro-benzene

Dendrimer

Oligomer

PbS CdS

Oligomer: CdS

CdS Rods

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

Acknowledgements

Alexandros Stravinadis Andrew Watt

Thankyou for listening!