Electron Injection from Copper Diimine Sensitizers into TiO2: Structural Effects and Their Implications for Solar Energy Conversion Devices

Research output: Contribution to journalJournal article – Annual report year: 2015Researchpeer-review

DOI

  • Author: Mara, Michael W.

    Northwestern University, United States

  • Author: Bowman, David N.

    North Carolina State University, United States

  • Author: Buyukcakir, Onur

    Korea Advanced Institute of Science and Technology, Korea, Republic of

  • Author: Shelby, Megan L.

    Northwestern University, United States

  • Author: Haldrup, Kristoffer

    Neutrons and X-rays for Materials Physics, Department of Physics, Technical University of Denmark, Fysikvej, 2800, Kgs. Lyngby, Denmark

  • Author: Huang, Jier

    Argonne National Laboratory, United States

  • Author: Harpham, Michael R.

    Argonne National Laboratory, United States

  • Author: Stickrath, Andrew B.

    Argonne National Laboratory, United States

  • Author: Zhang, Xiaoyi

    Argonne National Laboratory, United States

  • Author: Stoddart, J. Fraser

    Northwestern University, United States

  • Author: Coskun, Ali

    Korea Advanced Institute of Science and Technology, Korea, Republic of

  • Author: Jakubikova, Elena

    North Carolina State University, United States

  • Author: Chen, Lin X.

    Northwestern University, United States

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Copper(I) diimine complexes have emerged as low cost replacements for ruthenium complexes as light sensitizers and electron donors, but their shorter metal-to-ligand-charge-transfer (MLCT) states lifetimes and lability of transient Cu(II) species impede their intended functions. Two carboxylated Cu(I) bis-2,9-diphenylphenanthroline (dpp) complexes [Cu(I)(dpp-O(CH2CH2O)5)(dpp-(COOH)2)]+ and [Cu(I)(dpp-O(CH2CH2O)5)(dpp-(Φ-COOH)2)]+ (Φ = tolyl) with different linker lengths were synthesized in which the MLCT-state solvent quenching pathways are effectively blocked, the lifetime of the singlet MLCT state is prolonged, and the transient Cu(II) ligands are stabilized. Aiming at understanding the mechanisms of structural influence to the interfacial charge transfer in the dye-sensitized solar cell mimics, electronic and geometric structures as well as dynamics for the MLCT state of these complexes and their hybrid with TiO2 nanoparticles were investigated using optical transient spectroscopy, X-ray transient absorption spectroscopy, time-dependent density functional theory, and quantum dynamics simulations. The combined results show that these complexes exhibit strong absorption throughout the visible spectrum due to the severely flattened ground state, and a long-lived charge-separated Cu(II) has been achieved via ultrafast electron injection (<300 fs) from the 1MLCT state into TiO2 nanoparticles. The results also indicate that the TiO2-phen distance in these systems does not have significant effect on the efficiency of the interfacial electron-transfer process. The mechanisms for electron transfer in these systems are discussed and used to develop new strategies in optimizing copper(I) diimine complexes in solar energy conversion devices.
Original languageEnglish
JournalJournal of the American Chemical Society
Volume137
Issue number30
Pages (from-to)9670-9684
Number of pages15
ISSN0002-7863
DOIs
Publication statusPublished - 2015
CitationsWeb of Science® Times Cited: No match on DOI

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