1 / 21

Ultrafast processes in molecules

Ultrafast processes in molecules. VII – Organic photovoltaics. Mario Barbatti barbatti@kofo.mpg.de. Organic Photovoltaics (OPV). OPV advantages: Potential low cost Flexible, light, and thin Easy processing. Recent reviews: Mishra and Bäuerle , Angew Chem Int Ed 51 , 2020 (2012)

merrill
Download Presentation

Ultrafast processes in molecules

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Ultrafast processes in molecules VII – Organic photovoltaics Mario Barbatti barbatti@kofo.mpg.de

  2. Organic Photovoltaics (OPV) • OPV advantages: • Potential low cost • Flexible, light, and thin • Easy processing • Recent reviews: • Mishra and Bäuerle, AngewChemInt Ed 51, 2020 (2012) • Shang, Li, Meng, Wang, Shuai, TheorChemAcc129, 291 (2011) • Carsten, Vladimir, Rep ProgPhys73, 096401 (2010) • Brédas, Norton, Cornil, Coropceanu, AccChem Res 42, 1691 (2009)

  3. Efficiency h • Green, Emery, Hishikawa, Warta, Dunlop, Prog Photovolt 19, 565 (2011)

  4. Organic Photovoltaics (OPV) • OPV advantages: • Potential low cost • Flexible, light, and thin • Easy processing • OPV drawbacks • Low efficiency (recombination, low charge mobility) • Short lifetime (oxidation, photochemical degradation)

  5. OPV architecture Planar heterojunction (PHJ) Bulk heterojunction (BHJ) • a Mayer, Lloyd, Herman, Kasen, Malliaras, Appl Phys Lett 85, 6272 (2004) • b Sakai, Taima, Yamanari, Yoshida, Fujii, Ozaki, Jpn J Appl Phys 49, 032301 (2010) • c Sakai, Taima, Saito, Org Electron 9, 582 (2008)

  6. OPV operation J V Vmp VOC Jmp JSC • OPVs are characterized in terms of macro-quantities like h, VOC, and JSC • We do not expect to compute such quantities • But molecular computations may provide an indication of the adequacy of a D-A

  7. 1. Photoexcitation A A’ D D’ LE D’ 2. Exciton diffusion LE D 5. Recombination OPV photophysics 3. Charge transfer + - CT D→A 4. Charge separation + - CT D’→A’

  8. Ideal electronic structure D A 1. D shouldbephotoexcited Large oscillator strength between 500 nm and 700 nm 2. CT D→A should be quickly populated with hot polarons LE D should be above and near CT D→A LE Dbright 3. CT D→A should have a long lifetime Large energy gap between CT D→A and states below CT D→A GS • To check these features, we need to classify the electronic states of the D-A complex

  9. State classification Using a Mulliken partition: A B Degree of delocalization over A and B j Amount of CT between A and B i Considering a multielectronic wavefunction: • Crespo-Otero and Barbatti, TheorChem Acc 131, 1237 (2012)

  10. State classification

  11. Benchmarking… • Systematic investigation of the effects of: • D-A distance • D-A orientation • Oligomer size • Chemical environment • Chemical functionalization • Theoretical level

  12. Computationaldetails • wB97X-D • 6-31G(d) • S0D-A optimization • TDDFT: 40-70 states • G09 • State classification • Example: P3HT-PCBM • 240 atoms • 2 days (Xeon 3.3 GHz 10 cores) 3

  13. Dependence on functional • Extremely dependent on functional! • CTs are wrong without range-separation • C60 bands are blue shifted with range separation.

  14. Double excitations… • Constant blue shift between TDDFT and DFT/MRCI • Exceptions: states with large multiple excitation character

  15. Photophysics of D-A junctions LE Dbright CT D→A • How much does the electronic structure of the D-A complexes resemble the ”Ideal Electronic Structure”? GS

  16. Dependence on D-A distance • LOC does not show strong dependence on D-A distance • CT is stabilized at short distances (Coulomb r-1 is expected)

  17. Dependence on D-A orientation • LOCs are not affected • CTs are strongly affected • CTs are stabilized by stacking LOC(A) LOC(D) DELOC CT D→A CT A→D

  18. Dependence on D size • LOC(D)s are affected, but not LOC(A)s • CTs are affected

  19. Functionalization

  20. Environment

  21. Next lecture Quantum dynamicsmethods Contact barbatti@kofo.mpg.de

More Related