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.

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.

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.

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.

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.

Tommaso Marcato, Frank Krumeich, and Chih-Jen Shih

ACS Nano 2022 16 (11), 18459-18471

DOI: 10.1021/acsnano.2c06600

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.

M. Diethelm, A. Devižis, W.-H. Hu, T. Zhang, R. Furrer, C. Vael, S. Jenatsch, F. Nüesch, R. Hany

Adv. Funct. Mater. 2022, 32, 2203643. https://doi.org/10.1002/adfm.202203643

This research investigates the impact of electron and hole traps on the performance and lifespan of polymer light-emitting electrochemical cells (PLECs). The study aims to identify and analyze the role of these traps in PLECs, drawing parallels with their known impact on polymer light-emitting diodes (PLEDs).

The researchers fabricated PLECs using a super yellow (SY) polymer as the emitting material and employed various experimental techniques, including electrical driving and breaks, light irradiation, and long-term absorption and capacitance measurements. Optical and electrical simulations using Setfos provided further insights into device behavior.

The findings reveal that electron traps in PLECs share similar characteristics with those in PLEDs, suggesting a common origin in the semiconducting polymer. Notably, the study identifies two types of hole traps in PLECs: one type present in the intrinsic region, mirroring PLED behavior, and another type forming at the interface of the intrinsic and p-doped regions, specific to the PLEC architecture.

This research highlights the significant role of charge traps in limiting PLEC performance and longevity. The findings emphasize the need for strategies beyond conventional approaches to enhance PLEC stability, urging a focus on addressing the fundamental limitations posed by charge traps within the light-emitting polymer itself.

How Setfos Was Used

Setfos was used to perform optical and electrical simulations of the PLEC devices to better understand their properties, such as luminance versus emitter position.

How Paios Was Used

Paios was used to perform several different types of measurements on the PLEC devices:

Impedance measurements: Specifically, impedance measurements at 0 V with an alternating 70 mV signal were taken to determine the capacitance transients of the devices.

Current and light intensity transient measurements: The Paios measurement system was also used to measure how the current and light intensity changed over time. The light intensity was measured by using a photodiode to measure the photovoltage, and the relationship between the measured photovoltage and the corresponding radiance/luminance is explained in a different source.

How Phelos Was Used

Phelos was used to take angular-dependent electroluminescence (EL) measurements of the PLEC devices.

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.

Markus Regnat, Kurt P. Pernstich, Simon Züfle, and Beat Ruhstaller

ACS Applied Materials & Interfaces 10,31552 (2018)

https://doi.org/10.1021/acsami.8b09595

Abstract: From s-polarized, angle-dependent measurements of the electroluminescence spectra in a three-layer phosphorescent organic light-emitting diode, we calculate the exciton distribution inside the 35 nm thick emission layer. The shape of the exciton profile changes with the applied bias due to differing field dependencies of the electron and hole mobilities. A split emission zone with high exciton densities at both sides of the emission layer is obtained, which is explained by the presence of energy barriers and similar electron and hole mobilities. A peak in the transient electroluminescence signal after turn-off and the application of a reverse bias is identified as a signature of a split emission zone.

Sandra Jenatsch, Markus Regnat, Roland Hany, Matthias Diethelm, Frank Alain Nüesch, and Beat Ruhstaller

ACS Photonics 5, 1591 (2018)

https://pubs.acs.org/doi/abs/10.1021/acsphotonics.8b00047

Abstract:Light-emitting electrochemical cells (LECs) are one of the simplest electroluminescent devices and consist of a single emissive organic/salt layer sandwiched between two electrodes. The unique attribute of an operated LEC is the development of a pdoped/ intrinsic/n-doped (p-i-n) structure in the active layer in which the doped regions allow for facile transport of electronic charges to the intrinsic region, where charge recombination and light emission occur. However, due to the complex and simultaneous motion of ionic and electronic charges, the examination of the p-i- n structure and the zone where the light is emitted (EZ) is challenging during operation. By analyzing incident photon-tocurrent conversion efficiency and angular emission measurements with optical simulations, and correlating the results with capacitance measurements, we are able to obtain a clear picture of the p-i-n situation and the EZ within the active layer of a sandwich-type LEC during operation. It is found that the p-doped zone grows to the center of the active layer while the EZ stays closer to the metal electrode and is unchanged over time. Furthermore, optical simulations reveal that the determined EZ limits the external quantum efficiency of the LEC by outcoupling efficiencies of less than 10%.