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Reiker T, Liu Z, Winter C, Cappellari MV, Abradelo DG, Strassert CA, Zhang D, Zacharias H. Ultrafast electron dynamics in excited states of conjugated thiophene-fluorene organic polymer (pF8T2) thin films. Phys Chem Chem Phys 2024; 26:4736-4751. [PMID: 38251969 DOI: 10.1039/d3cp00502j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2024]
Abstract
The electronic states of poly(9,9-dioctylfluorenyl-alt-bithiophene) pF8T2 on H/Si(100) substrates, prototypical for organic photovoltaics, were investigated by ultrafast photoelectron spectroscopy and by time-resolved fluorescence studies. Occupied and unoccupied electronic states were analysed by ultraviolet photoelectron spectroscopy (UPS), static and dynamic femtosecond two-photon photoemission (2PPE), and time-correlated single photon counting (TCSPC). Time-resolved measurements allow assessment of population lifetimes of intermediate states. The combination of time-resolved photoelectron spectroscopy and fluorescence excitation allows following the electronic dynamics in excited states from the femtosecond to the nanosecond time scale. For this prototypical material the electron kinetic energy resolved lifetimes range from about a few tens of femtoseconds up to hundreds of picoseconds. After annealing these types of organic thin films the efficiency of organic solar cells usually increases. We show that annealing does not influence the initial ultrafast charge generation processes, but the long-lived states. However, the nanosecond scale fluorescence lifetimes measured by TCSPC are prolonged after annealing, which therefore is identified as the cause of a greater exciton diffusion range and thus is beneficial for charge carrier extraction.
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Affiliation(s)
- T Reiker
- Center for Soft Nanoscience, University of Münster, 48149 Münster, Germany.
- Physics Institute, University of Münster, 48149 Münster, Germany
| | - Z Liu
- Organic Solids Laboratory, Institute of Chemistry, Chinese Academy of Science, Beijing 100190, P. R. China
| | - C Winter
- Physics Institute, University of Münster, 48149 Münster, Germany
| | - M V Cappellari
- Center for Nanotechnology and Institute for Inorganic and Analytical Chemistry, University of Münster, Heisenbergstraße 11, 48149 Münster, Germany
| | - D Gonzalez Abradelo
- Center for Nanotechnology and Institute for Inorganic and Analytical Chemistry, University of Münster, Heisenbergstraße 11, 48149 Münster, Germany
| | - C A Strassert
- Center for Nanotechnology and Institute for Inorganic and Analytical Chemistry, University of Münster, Heisenbergstraße 11, 48149 Münster, Germany
| | - D Zhang
- Organic Solids Laboratory, Institute of Chemistry, Chinese Academy of Science, Beijing 100190, P. R. China
| | - H Zacharias
- Center for Soft Nanoscience, University of Münster, 48149 Münster, Germany.
- Physics Institute, University of Münster, 48149 Münster, Germany
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