Rigorous Determination of Dipole Orientation in Organic Thin Films Using Angle-Dependent Photoluminescence
Yeonghoon Jin, Hyung Suk Kim, Donggyun Lee, Chihaya Adachi, Seunghyup Yoo, and Kyoungsik Yu
The Journal of Physical Chemistry C 2024 128 (4), 1755-1761
https://doi.org/10.1021/acs.jpcc.3c06330
This study introduces a rigorous analysis comparing distributed and concentrated dipole models in organic thin films using angle-dependent photoluminescence, highlighting inaccuracies in TDM orientation assumptions for thick emitter layers. It emphasizes considering the spatial distribution of TDMs, especially as film thickness increases, for precise OLED optical design.
How Phelos was used
Phelos was utilized for optical characterization via angle-dependent photoluminescence spectroscopy, aligning experimental setups and validating the necessity of considering distributed dipole models for accurate TDM orientation analysis in thick films.
On the Orientation Mechanism of Nonpolar Dyes in Light-Emitting Guest–Host Systems
Binh Minh Nguyen, Markus Schmid, Johann Kirsch, Albin Cakaj, and Wolfgang Brütting
Chemistry of Materials 2023 35 (17), 7333-7343
DOI: 10.1021/acs.chemmater.3c01804
The research explores how four nonpolar dyes orient within neat films and doped guest-host systems in organic light-emitting diodes (OLEDs). It identifies shape anisotropy and the relationship between the substrate temperature during deposition and the system's glass transition temperature (Tg) as critical to the alignment of emissive transition dipoles. Notably, in mixed cohost systems with components of differing Tgs, the alignment may not align with the mixed host's effective Tg. The study also proposes using a molecule's principal moments of inertia to assess its reorientation resilience and aspect ratio to gauge shape anisotropy.
How Phelos was used
Angular-Dependent Photoluminescence measurements were performed with Phelos.
Heteroleptic Ir(III)‑based near‑infrared organic light‑emitting diodes with high radiance capacity
Park, Y., Lee, G.S., Lee, W. et al.
Sci Rep 13, 1369 (2023).
https://doi.org/10.1038/s41598-023-27487-6
Researchers have designed Ir(III)-based heteroleptic NIR materials for near-infrared organic light-emitting diodes (NIR OLEDs) with a focus on radiance capacity (RC) rather than just radiance. The emitters exhibit a highly oriented horizontal dipole ratio, short radiative lifetime, and extremely low turn-on voltage.
The device demonstrates a high RC of 720 mW/sr/m2/V, making it a standout performer among Ir(III)-based NIR OLEDs with similar emission peaks, and has potential applications in healthcare, authentication, and night vision displays.
Measurement of the angle dependent p‑polarized photoluminescent spectrum (ADPL). The emission layer was deposited on a bare 50 nm-thick glass substrate. Then, glass encapsulation was done in a nitrogen ( N2)-filled glove box to avoid degradation from the air. A full angle dependent p-polarized PL spectrum was obtained with the goniometer based motorized intensity measurement system Phelos.
Heteroleptic Ir(III)-based near-infrared organic light-emitting diodes with high radiance capacity
Park, Y., Lee, G.S., Lee, W. et al.
Sci Rep 13, 1369 (2023).
https://doi.org/10.1038/s41598-023-27487-6
Researchers have developed new Ir(III)-based heteroleptic NIR materials for near-infrared organic light-emitting diodes (NIR OLEDs) with heavy metals, which have a highly oriented horizontal dipole ratio and short radiative lifetime. These emitters offer an extremely low turn-on voltage and high radiance capacity, making them suitable for various applications such as healthcare services, veil authentication, and night vision displays. This study demonstrates exceptional device performance among similar Ir(III)-based NIR OLEDs, which makes it a promising material for commercial applications.
Measurement of the angle dependent p-polarized photoluminescent spectrum (ADPL)
The emission layer was deposited on a bare 50 nm-thick glass substrate. Then, glass encapsulation was done in a nitrogen (N2)-filled glove box to avoid degradation from the air. A full angle dependent p-polarized PL spectrum was obtained with the goniometer based motorized intensity measurement system Phelos, Fluxim.
Donor or Acceptor: Molecular Engineering Based on dibenzo[a,c]phenazine Backbone for Highly Efficient Thermally-Activated Delayed Fluorescence Organic Light-Emitting Diodes
Liu, Y., Yang, J., Mao, Z., Ma, D., Wang, Y., Zhao, J., Su, S.-J., Chi, Z.,
Adv. Optical Mater. 2023, 2201695
DOI: 10.1002/adom.202201695
The article reports on the development of three thermally-activated delayed fluorescence (TADF) molecules with different donor-acceptor (D-A) frameworks, namely D-A, D-A-D, and D-A-A. The TADF molecules were evaluated for their photophysical and electroluminescence properties. The study found that the TADF molecule with the D-A-A framework achieved the best performance in terms of external quantum efficiency due to its low energy gap between singlet and triplet, effective reverse intersystem crossing, high photoluminescence quantum yield, and horizontal dipole ratio. The study provides insights into the design of efficient TADF emitters.
P-polarized angle-dependent light emissions of CBP doped films were measured by Fluxim using Phelos. Refractive index of the materials was measured by MEL broadband spectroscopic Mueller matrix ellipsometer or extracted by Setfos database. The light out-coupling efficiency of devices was simulated by Setfos.
Confinement-Tunable Transition Dipole Moment Orientation in Perovskite Nanoplatelet Solids and Binary Blends
Tommaso Marcato, Frank Krumeich, and Chih-Jen Shih
ACS Nano 2022 16 (11), 18459-18471
Tuning the transition dipole moment (TDM) orientation in low-dimensional semiconductors is of fundamental and practical interest, as it enables high-efficiency nanophotonics and light-emitting diodes. However, despite recent progress in nanomaterials physics and chemistry, material systems that allow continuous tuning of the TDM orientation remain rare.
Here, combining k-space photoluminescence spectroscopy and multiscale modeling, we demonstrate that the TDM orientation in lead halide perovskite (LHP) nanoplatelet (NPL) solids is largely confinement-tunable through the NPL geometry that regulates the anisotropy of Bloch states, dielectric confinement, and exciton fine structure.
The experimental data were evaluated with the software Setfos provided by Fluxim.
The angle-dependent PL of the NPL film was characterized using the commercial instrument Phelos (Fluxim Inc.) equipped with a spectrometer, a linear polarizer, and a cylindrical macro extractor lens.
Elucidating the role of two-dimensional cations in green perovskite light emitting diodes,
Aurimas Vyšniauskas, Simon Keegan, Kasparas Rakstys, Tobias Seewald, Vytautas Getautis, Lukas Schmidt-Mende, Azhar Fakharuddin
Organic Electronics, Volume 111, 2022, 106655, ISSN 1566-1199
doi.org/10.1016/j.orgel.2022.106655
Perovskite light emitting diodes (PeLEDs) have emerged as promising candidates for applications requiring visible and near-infrared emission.
In this work, the researchers demonstrate the importance of compositional tuning using three different 2D cations namely phenylethylammonium (PEA), its monofluorinated analogue FPEA and a custom-made bulkier cation BPEA containing an extra phenyl ring.
Their results show that the tuning of the ratio between 2D cation and the [PbX6]4- provides a trade-off between electrical transport in the device and the emission properties of the emissive layer.
Generally, a large excess of cations is required to enhance the external quantum efficiency (EQE) of PeLEDs. Among the various cations, FPEA leads to PeLEDs with the highest EQE up to 7.7%, while BPEA resulted in the smallest EQE.
External quantum efficiencies (EQEs), current density-voltage-luminance dependencies, electroluminescence spectra and lifetimes were measured using Fluxim’s Phelos angular luminescence spectrometer. EQE and lifetime measurements were performed at 1 mA current. EQE measurements were performed at a given current density to minimize time for characterisation and degradation of the device. Absorbance of the perovskite films were measured using Agilent Cary 5000 UV-Vis-NIR spectrometer.
Anisotropic nanocrystal superlattices overcoming intrinsic light outcoupling efficiency limit in perovskite quantum dot light-emitting diodes
Sudhir Kumar, Tommaso Marcato, Frank Krumeich, Yen-Ting Li, Yu-Cheng Chiu and Chih-Jen Shih
Nat Commun. (2022), 13, 2106
https://www.nature.com/articles/s41467-022-29812-5
The intrinsic light outcoupling efficiency of quantum dots remains considerably lower than the organic counterpart.
The authors, using the colloidal lead halide perovskite anisotropic nanocrystals (ANCs) as a model system, report a directed self-assembly approach to form an anisotropic nanocrystal superlattice of perovskite nanocrystals. The emission polarization in individual ANCs rescales the radiation from horizontal and vertical transition dipoles, effectively resulting in preferentially horizontal TDM orientation. The optimized single-junction QD LEDs showed peak external quantum efficiency of up to 24.96%, comparable to state-of-the-art organic LEDs.
Optical Outcoupling Efficiency of Organic Light-Emitting Diodes with a Broad Recombination Profile
Yungui Li, Naresh B. Kotadiya, Bas van der Zee, Paul W. M. Blom, and Gert-Jan A. H. Wetzelaer
Adv. Optical Mater. 2021, 2001812,
https://onlinelibrary.wiley.com/doi/full/10.1002/adom.202001812
The authors developed a numerical model to simulate the fraction of photons coupled to air for OLEDs with a broad recombination zone. The dipole orientation of the CzDBA neat film was determined with Phelos by fitting the angular dependence of photoluminescence with Setfos software from Fluxim.