Organic Electronics

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

2. Issues Nanophysics group • 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?

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

4. Cu conductor Fe Si insulator polyethylene Conductivity scale s (W-1cm-1) • Conductivity = 1 / Resistivity 106 104 102 semiconductor 1 (100) 10-2 10-4 10-6 10-8 10-10 10-12 10-14 10-16

5. many atoms Energy levels in materials single atom electron energy 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.

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

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

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

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

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

11. Energy light Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Semiconductors

12. As Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si As As Si Si Si Si Si Si Si Si Si Si Semiconductors • Donor

13. As B As Si B Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Semiconductors • Acceptor

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

15. Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Semiconductors - +

16. Cu conductor Fe { Doped Si Si insulator polyethylene Conductivity scale s (W-1cm-1) • Conductivity = 1 / Resistivity 106 104 102 semiconductor 1 (100) 10-2 10-4 10-6 10-8 10-10 10-12 10-14 10-16

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

18. We have: • bound electrons between the atoms in the ring (sp2) • A cloud of partly free electrons above and below the ring (p-electrons) How do molecules act as semiconductors? • We must have alternating single and double bonds

20. Cu conductor Fe { Doped Si polymer semiconductors Si insulator polyethylene Conductivity scale s (W-1cm-1) 106 104 102 semiconductor 1 (100) 10-2 10-4 10-6 10-8 10-10 10-12 10-14 10-16

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

24. Flexible displays

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

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

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

28. n E Organic solar cell PPV C60

29. n ( ) E Organic solar cell Donor Acceptor ITO Al Glass PPV C60

30. n ( ) ( ) E Organic solar cell Donor Acceptor ITO Al Glass PPV C60 Problem: The exciton can only travel < 20 nm before the electron and hole recombine

31. n Organic solar cell Donor Acceptor ITO Al Glass PPV C60 Need to create exciton <20nm from an interface

32. n E Organic solar cell Donor Acceptor ITO Al Glass PPV C60

33. Organic solar cell Donor Acceptor ITO Al Glass PPV C60 - +

34. Organic solar cell Donor Acceptor ITO Al Glass PPV C60 - +

35. Organic solar cell Donor Acceptor ITO Al Glass PPV C60 - +

37. Organic solar cells Organic Solar Cells University of Linz 10 x 15 cm ; Active area : 80 cm2

41. Grazing incidence x-ray diffraction

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

43. Solarmer

44. Molecular solar cells

45. Molecular solar cells

46. Photosynthesis

47. Photosynthesis: at the molecular level

49. Summary Nanophysics group • 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