Solid-State Solvation and Enhanced Exciton Diffusion in Doped Organic Thin Films under Mechanical Pressure

Journal Article · Thu Apr 02 00:00:00 EDT 2015 · ACS Nano

DOI:https://doi.org/10.1021/acsnano.5b00938· OSTI ID:1370966

Chang, Wendi ^[1]; Akselrod, Gleb M. ^[2]; Bulović, Vladimir ^[1]

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1. Massachusetts Inst. of Technology, Cambridge, MA (United States). Dept. of Electrical Engineering and Computer Science
2. Univ. of Duke, Durham, NC (United States). Dept. of Electrical and Computer Engineering

Direct modification of exciton energy has been previously used to optimize the operation of organic optoelectronic devices. One demonstrated method for exciton energy modification is through the use of the solvent dielectric effects in doped molecular films. To gain a deeper appreciation of the underlying physical mechanisms, we test the solid-state solvation effect in molecular thin films under applied external pressure. We observe that external mechanical pressure increases dipole–dipole interactions, leading to shifts in the Frenkel exciton energy and enhancement of the time-resolved spectral red shift associated with the energy-transfer-mediated exciton diffusion. Measurements are performed on host:dopant molecular thin films, which show bathochromic shifts in photoluminescence (PL) under increasing pressure. This is in agreement with a simple solvation theory model of exciton energetics with a fitting parameter based on the mechanical properties of the host matrix material. We measure no significant change in exciton lifetime with increasing pressure, consistent with unchanged aggregation in molecular films under compression. However, we do observe an increase in exciton spectral thermalization rate for compressed molecular films, indicating enhanced exciton diffusion for increased dipole–dipole interactions under pressure. The results highlight the contrast between molecular energy landscapes obtained when dipole–dipole interactions are increased by the pressure technique versus the conventional dopant concentration variation methods, which can lead to extraneous effects such as aggregation at higher doping concentrations. The present work demonstrates the use of pressure-probing techniques in studying energy disorder and exciton dynamics in amorphous molecular thin films.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Center for Excitonics (CE)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: SC0001088
• OSTI ID: 1370966
• Journal Information: ACS Nano, Journal Name: ACS Nano Journal Issue: 4 Vol. 9; ISSN 1936-0851
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Förster radiative energy transfer
Onsager dielectric theory
charge transport
optics
organic semiconductor
photosynthesis (natural and artificial)
pressure probing
solar (photovoltaic)
solid state lighting
solid-state solvation effect
synthesis (novel materials)
synthesis (scalable processing)
synthesis (self-assembly)