Most organic thin film semiconductors have a short exciton diffusion length of about 10 nm due to energy barrier constraints. In contrast, singlet excitons in purified single crystals are known to have a much larger diffusion range (up to 220 nm). However, in these cases, the size of these materials is often polydisperse and there are certain problems in incorporating devices. Device development therefore relies on the ability to develop uniform nanostructures that are suitable for processing and capable of supporting remote exciton diffusion.
[Introduction]
Richard H., University of Cambridge Friend, University of Bristol, George R. Whittell, Professor Ian Manners (co-communication author) and first author Xu-Hui Jin published an article entitled "Long-range exciton transport in co njugated polymer nanofibers prepared by seeded growth" in Science. Jin et al. prepared nanofibers from a block polymer composed of a radioactive nucleus surrounded by a corona of polyethylene glycol and polythiophene. The excitons generated in the polyfluorene cannot enter the polyethylene glycol layer, so the diffusion exceeds 200 nm. This distance can be adjusted by varying the length of the polyethylene glycol, which may have potential for use in the development of organic devices such as photovoltaics.
[Graphic introduction]
Figure 1 Segmented PDHF nanofiber multi-step self-assembly
(a) Seed crystal growth process and schematic diagram of PDHF14-b-PEG227 and PDHF14-b-QPT22
(b) Segmented B-A-B nanofiber structure
(c) Uniform absorption and photoluminescence emission
Figure 2 Photoluminescence of segmented PDHF B-A-B nanofibers in solution
(a) LSCM image with center and end Ln values ​​of 1.6 μm and 0.9 μm, respectively
(b) PL spectra of segmented PDHF nanofibers with different lengths of segment A; emission induced by direct excitation of QPT in 1605 nm samples has not been resolved.
Fig.3 PL spectra and kinetics of transient gratings of segmented PDHF B-A-B nanofibers
(a) Transient grating PL time slices with a segmented nanofiber solution (0.5 mg / ml) with an average A segment length of 775 nm showed energy transfer from PDHF to QPT receptor corona. The core PDHF I0-1 peak decays due to exciton quenching and quenching to the acceptor.
(b) PDHF attenuates the normalized PL kinetics and the rise of the QPT signal of the spectrum shown in (A). The green line shows the PDHF signal (430-460 nm); the blue line indicates QPT PL (530 nm-630 nm). The solvent used was THF: MeOH 1:1.
Figure 4: Transient PL dynamic size dependence and corresponding diffusion length model fitting
(a) Transient grating PL dynamics (square) of PDHF PL signal (430 nm - 460 nm), PL decay time decreases with decreasing fragment length, showing effective transfer
(b) Corresponding PL dynamics of the QPT signal rise (square)
(c) Transient grating spectroscopy of PDHF-b-PEG nanofibers in solution
ã€summary】
Spectroscopic measurements in solution indicate that these nanostructures exhibit long-range exciton transport on a critical length scale comparable to the length of light absorption in the conjugated polymer, and this is achieved by a high degree of structural order in the PDHF core. This diffusion length allows light-trapping devices employing these polymer structures as antennas to be coupled to a finite-absorbance photodetector material.
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