1. Organic Electronics J Emyr Macdonald, School of Physics and Astronomy Nanophysics group

2. Issues We have had electronics and solar cells made from semiconductors like silicon for years. Could we make electronics from molecules or plastic? What would the benefits be? –Cheaper than silicon to produce –Flexible sheets Has anyone seen solar cells made from molecules? Today? Nanophysics group

3. http://www.wbgu.de/wbgu_jg2003_kurz_engl.pdf World in Transition – Towards Sustainable Energy Systems German Advisory Council on Global Change Berlin, 2003

4. Conductivity = 1 / Resistivity 10 6 10 4 10 2 1 (10 0 ) 10 2 10 4 10 6 10 8 10 10 12 10 14 10 16 Cu Fe polyethylene Si conductor insulator semiconductor ( -1 cm -1 ) Conductivity scale

5. Energy levels in materials Electrons can only occupy one level. The first electron will occupy the lowest energy level. The next electron will have to go into a higher energy level. many atoms single atom electron energy

6. Energy levels in materials single atom many atoms metal insulatorsemiconductor bandgap electron energy

7. Conduction in semiconductors semiconductor bandgap thermal (heat energy) light heat light For the semiconductor to conduct we need to provide the electrons with energy greater than the bandgap. electron energy bound to atom free to move There are two possible sources of energy to excite electron across bandgap:

8. Conduction in semiconductors semiconductor bandgap thermal (heat energy) light heat light For the semiconductor to conduct we need to provide the electrons with energy greater than the bandgap. electron energy bound to atom free to move There are two possible sources of energy to excite electron across bandgap:

9. Conduction in semiconductors semiconductor bandgap thermal (heat energy) light heat light For the semiconductor to conduct we need to provide the electrons with energy greater than the bandgap. electron energy bound to atom free to move There are two possible sources of energy to excite electron across bandgap:

10. Demo: effect of wavelength of light semiconductor electron energy red 650 nm violet 470 nm

11. Semiconductors Si light Energy

12. Semiconductors Donor Si As

13. Semiconductors Si As B B Acceptor

14. Semiconductors Si What happens when we apply a voltage?

15. Semiconductors Si + -

16. Conductivity = 1 / Resistivity 10 6 10 4 10 2 1 (10 0 ) 10 2 10 4 10 6 10 8 10 10 12 10 14 10 16 Cu Fe polyethylene Si { Doped Si conductor insulator semiconductor ( -1 cm -1 ) Conductivity scale

17. Nobel Prize in Chemistry 2000 For the Discovery and Development of Conductive Polymers Alan Heeger University of California at Santa Barbara Alan MacDiarmid University of Pennsylvania Hideki Shirakawa University of Tsukuba Nobel Prize for Chemistry 2000

18. How do molecules act as semiconductors? We must have alternating single and double bonds We have: bound electrons between the atoms in the ring (sp 2 ) A cloud of partly free electrons above and below the ring ( -electrons)

20. 10 6 10 4 10 2 1 (10 0 ) 10 2 10 4 10 6 10 8 10 10 12 10 14 10 16 Cu Fe polyethylene Si { Doped Si conductor insulator semiconductor ( -1 cm -1 ) polymer semiconductors Conductivity scale

21. Organic Light-Emitting Diodes Glass Cathode (ITO) Conjugated Material Anode (Al) V R.H. Friend et al., Nature 397, 121 (1990) Energy Organic light-emitting diode (OLED)

24. Flexible displays

25. Benefits for Organic Electronics Weight Flexibility Relatively simple processing Large areas (displays) Cost Disadvantage: Slow compared to silicon

26. Applications for Molecular Electronics Electronic paper Low-cost chips (e.g. packaging …) Solar energy Displays

27. Solar Cell: demonstration The plotted voltage is proprtional to light intensity – this is shown vs. time time voltage

28. Organic solar cell n C 60 PPV E

29. n C 60 ( ) PPV E Glass ITO DonorAcceptor Al Organic solar cell

30. n C 60 ( ) PPV ( ) Problem: The exciton can only travel < 20 nm before the electron and hole recombine E Glass ITO DonorAcceptor Al Organic solar cell

31. n C 60 PPV Need to create exciton <20nm from an interface Glass ITO DonorAcceptor Al Organic solar cell

32. n C 60 PPV E Glass ITO DonorAcceptor Al Organic solar cell

33. C 60 PPV + - Glass ITO DonorAcceptor Al Organic solar cell

34. C 60 PPV + - Glass ITO DonorAcceptor Al Organic solar cell

35. C 60 PPV + - Glass ITO DonorAcceptor Al Organic solar cell

37. Organic Solar Cells University of Linz 10 x 15 cm ; Active area : 80 cm 2 Organic solar cells

41. Grazing incidence x-ray diffraction

42. Scanning Probe Microscopy MDMO-PPV: PCBM blend P3HT: PCBM blend

43. Solarmer

44. Molecular solar cells

46. Photosynthesis

47. Photosynthesis: at the molecular level

49. Summary Metals, insulators and semiconductors Molecules and energy levels Some new devices made from plastic electronics Solar energy and world energy requirements Current developments in molecular solar cells Photosynthesis: the oldest and most advanced solar cell technology Nanophysics group