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Li XZ, Dai ST, et al. Light-induced enhancement of exciton transport in organic molecular crystal. Opto-Electron Adv 8, 240207 (2025). doi: 10.29026/oea.2025.240207
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Light-induced enhancement of exciton transport in organic molecular crystal
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Abstract
Efficient exciton transport over long distances is crucial for organic optoelectronics. Despite efforts to improve the transport properties of organic semiconductors, the limited exciton diffusion remains a significant obstacle for light-harvesting applications. In this study, we observe phenomena where exciton transport is significantly enhanced by light irradiation in the organic molecular crystal of 2,2'-(2,5-bis(2,2-diphenylvinyl)-1,4-phenylene) dinaphthalene (BDVPN). The exciton transport in this material is improved, as evidenced by the increased diffusion coefficient from 10−3 cm2·s−1 to over 1 cm2·s−1 and a prolonged diffusion length from less than 50 nm to nearly 700 nm characterized by time-resolved photoluminescence microscopy (TPLM). Additionally, we confirmed the enhancement of charge transport capability under irradiation as additional evidence of improved transport properties of the material. These intriguing phenomena may be associated with the material’s twisted molecular conformation and rotatable single bonds, which facilitate light-induced structural alterations conducive to efficient transport properties. Our work provides a novel insight into developing organic semiconductors with efficient exciton transport. -
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References
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Supplementary Information
Supplementary information for Light-induced enhancement of exciton transport in organic molecular crystal 
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Li XZ, Dai ST, et al. Light-induced enhancement of exciton transport in organic molecular crystal. Opto-Electron Adv 8, 240207 (2025). doi: 10.29026/oea.2025.240207
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Figure 1.
Crystal geometries and basic optical properties. (a) Chemical structure. (b) Optical microscope image of a BDVPN crystal under UV light (365 nm) (up) and schematic growth morphology of the crystal (down). (c) Schematic diagram of molecular packing viewed from a-axis. BDVPN molecules present herringbone packing mode and are aligned layer by layer along the b-axis (long axis of the crystal). (d) UV-vis and PL spectra, and (e) Time-resolved PL of the BDVPN crystal.
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Figure 2.
Irradiation-induced exciton diffusion enhancing and the roles of oxygen and water. (a) Schematic of the home-built TPLM. The PL signal is magnified at the image plane, as shown in (b), and the time-resolved APD is scanned across the PL spot to generate a spatial-temporal map of PL intensity. (c) The spatial-temporal PL intensity map of a BDVPN crystal before and after irradiation treatment by a collimated strip-shaped 405 nm CW laser (4 W cm−2). (d) The measured MSD over time of the BDVPN crystal after being irradiated for 0 minutes (before irradiation), 10 minutes, 45 minutes. The solid lines show the results of linear fit, and resulting three diffusion coefficients of 0.0030±0.0036 cm2·s−1, 0.036±0.006 cm2·s−1, and 0.18±0.02 cm2·s−1. (e) The evolution of exciton diffusion coefficient of two BDVPN crystals under irradiation, where one crystal was exposed to ambient air and the other to a nitrogen environment.
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Figure 3.
Impact of long period irradiation in nitrogen cabinet on diffusion parameters and PL properties. (a) The evolution of exciton diffusion coefficient after irradiation. The values are statistics results, each taken from several tests (see section SI1, Supporting Information). The inset shows the data corresponding to the first stages (blue dashed area) under logarithmic coordinates. (b) The fast broadening of PL emission over time for the BDVPN crystal irradiated for 145 hours. Compared with Fig. 2(c), the enhancement in exciton diffusion was visualized. (c) The evolution of exciton lifetime and diffusion length after irradiation. (d) Redshift of PL spectra with irradiation time.
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Figure 4.
Enhancement of charge transport under irradiation. (a) Schematic and optical microscope images of the electrical device, two Au film electrodes were transferred to the crystal. (b) The evolution of dark current (at a 60 V applied voltage) of the BDVPN crystal over time before and after the irradiation treatment (405 nm CW laser, 60 mW ·cm−2).
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Figure 5.
Intermolecular interactions analysis. (a) The isosurface map of the IRI for the BDVPN crystal. IRI analysis provides additional insights into intra- and intermolecular interactions through gradient isosurfaces and corresponding colors (determined by sign(λ2)ρ values). (b) Molecular packing and intermolecular interactions of the crystal (The molecules drawn in orange and blue are the same conformation but arranged in different directions). (c) Hirshfeld surface of the BDVPN crystal. The red spots represent the close contact of C···H.
