1. Reporter: Ting Lei Supervisor: Prof. Jian Pei Organic Solar Cells 2009/10/23 Mechanism and Design Strategies

2. Contents Molecular Understanding 1 Important Factors 2 Design Strategies 3

3. Pictures From http://www.konarka.com/

4. Various Solar Cells Solar CellOrganicDSSCBHJInorganicTraditional Quantum Dot Sensitized DSSC: Dye Sensitized Solar Cells (Grätzel Cell) BHJ: Bulk Heterojunction Solar Cells

5. Molecular Understanding Bredas, J.-L. et. al. Acc. Chem. Res. 2009, ASAP

6. Electronic Diagram Bredas, J.-L. et. al. Acc. Chem. Res. 2009, ASAP

7. Optical absorption characteristics: 1.Intense: wave function overlap between ground and excited state 2.Broad: geometry relaxation Benefits: Large extinction coefficients; Good match with solar spectrum Drawbacks: Strong electron-vibration coupling--- relaxation; Singlet state Alex, K.-Y. Jen, et. al. J. Am. Chem. Soc. 2009, 131,13886-13887

8. Exciton Migration Exciton Migration: 1.Exciton diffusion: L=(Dτ) 1/2 2.Generation center and Dissociation center Improving the migration: 1.Large diffusion length (70nm for pentacene) 2.Singlet diffusion or Triplet diffusion? FRET long range & quickly Dexter short range & long life Heremans, P. et. al. Acc. Chem. Res. 2009, ASAP

9. Exciton Dissociation CT/CS States at the D/A Heterojunction

10. Charge-Carrier Mobility In organic semiconductors: 1.Weakness of the electronic couplings 2.The large electron-vibration couplings 3.The disorder effects Highly disordered amorphous films (typically, 10 -6 -10 -3 cm 2 V -1 s -1 ) Highly ordered materials (>1 cm 2 V -1 s -1 ).

11. Charge Collection at Electrodes Workfunction EAIP

12. J-V Curves

13. Origin of the J sc Solar spectrum Amount of J EQE

14. Origin of V oc

15. Important Factor 1 – Bandgap Solutions Tandem Cells 1. Large Ancenes 2. Charge Transfer

16. Important Factor 2 – HOMO Level

17. Yu, L. J. Am. Chem. Soc. 2009, 131, 56-57

18. Important Factor 2 – HOMO Level Li, G. et. al. J. Am. Chem. Soc. 2009, ASAP

19. Important Factors 2 – HOMO Level

20. Important Factor 3 – Charge Mobility Cornil, J. et. al. Adv. Mater. 2007, 19, 1791-1799

21. Important Factor 4 – Surface Morphology Bazan, G. C. et. al. Nat. Mater. 2007, 6, 497-500

22. Important Factor 4 – Surface Morphology

23. Design Strategies Cao, Y. et. al. Acc. Chem. Res. 2009, ASAP

24. Design Strategies Benzothiadiazole-Containing Polymers

25. Design Strategies Thiophene-Based Polymers

26. Design Strategies Thienopyrazine-Containing PolymersQuinoxaline-Containing Polymers Substituted Silole-Containing Polymers

27. Design Strategies

28. Summary

29. Our Approach Important Factors 1 & 2– Bandgap & V oc Important Factors 3 & 4– Charge Mobility & Morphology Transition Dipole

30. Acknowledgement  感谢裴坚老师  感谢有机所所有老师  感谢实验室的所有成员