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 Oligomer Cadmium acetate Toluene DMSO 110°C Sulphur flakes in toluene Oligomer: CdS in chloro- benzene Dendrimer Oligomer PbSCdS

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!