Ultrafast spectroscopy reveals singlet fission, ionization and excimer formation in perylene film

Wenjun Ni,Gagik G Gurzadyan,Licheng Sun

doi:10.1038/s41598-021-83791-z

Wenjun Ni, Gagik G Gurzadyan + Show 1 more

Open Access

https://doi.org/10.1038/s41598-021-83791-z

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Abstract

Singlet exciton fission (SF) is a spin-allowed process whereby two triplet excitons are created from one singlet exciton. This phenomenon can offset UV photon energy losses and enhance the overall efficiency in photovoltaic devices. For this purpose, it requires photostable commercially available SF materials. Excited state dynamics in pure perylene film, ease of commercial production, is studied by time-resolved fluorescence and femtosecond transient absorption techniques under different photoexcitation energies. In film, polycrystalline regions contain perylene in H-type aggregate form. SF takes place from higher excited states of these aggregates in ultrafast time scale < 30 fs, reaching a triplet formation quantum yield of 108%. Moreover, at λex = 450 nm singlet fission was detected as a result of two-quantum absorption. Other competing relaxation channels are excimer (1 ps) and dimer radical cation formation (< 30 fs). Excimer radiatively relaxes within 19 ns and radical cation recombines in 3.2 ns. Besides, exciton self-trapping by crystal lattice distortions occurs within hundreds of picosecond. Our results highlight potential of simple-fabricated perylene films with similar properties as high-cost single crystal in SF based photovoltaic applications.

Highlights

Singlet exciton fission (SF) is a spin-allowed process whereby two triplet excitons are created from one singlet exciton
Morphological characterization of perylene film has been performed by use of scanning electron microscope (SEM) and atomic force microscopy (AFM) techniques
The cubic perylene nanoaggregates are clearly seen from SEM (Fig. S1a), distributed homogenously on the surface

Summary

Introduction

Singlet exciton fission (SF) is a spin-allowed process whereby two triplet excitons are created from one singlet exciton. The absorption, fluorescence and excitation emission spectra of perylene film evaporated onto the fused silica plate are shown in Fig. 1a (solid curves). It should be noted that the discrepancy between absorption and fluorescence excitation spectra in the range of 250–310 nm is indicative of a photophysical process, which proceeds directly from the higher excitonic state bypassing S1 state, viz.

Results

Conclusion