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

Contents Molecular Understanding 1 Important Factors 2 Design Strategies 3

Pictures From

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

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

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

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,

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

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

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, cm 2 V -1 s -1 ) Highly ordered materials (>1 cm 2 V -1 s -1 ).

Charge Collection at Electrodes Workfunction EAIP

J-V Curves

Origin of the J sc Solar spectrum Amount of J EQE

Origin of V oc

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

Important Factor 2 – HOMO Level

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

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

Important Factors 2 – HOMO Level

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

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

Important Factor 4 – Surface Morphology

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

Design Strategies Benzothiadiazole-Containing Polymers

Design Strategies Thiophene-Based Polymers

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

Design Strategies

Summary

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

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