Necessity of submonolayer LiF anode interlayers for improved device performance in blue phosphorescent OLEDs

Lee, Seung Il; Liang, Kunyu; Hui, Lok Shu; Arbi, Ramis; Munir, Muhammad; Lee, Seok Je; Kim, Jin Wook; Kim, Ki Ju; Kim, Woo Young; Turak, Ayse

doi:10.1007/s10854-020-04889-0

Cited by 10 publications

(7 citation statements)

References 71 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[81] Nonetheless, it is widely reported that thermally evaporated LiF films show a granular and porous morphology, with large surface roughness. [82][83][84] Moreover, due to its effectiveness in the sub-nanometer thickness range, the LiF layers obtained suffer from deficient surface coverage. All these features contribute actively towards the creation of preferential channels through which the charges are more prone to be injected into the electron transport material (ETM); in fact, our fresh samples show tiny dark regions evenly distributed along the light-emitting area under device operation, that correspond to more resistive regions through which the charge carrier conductivity is hampered.…”

Section: Discussionmentioning

confidence: 99%

Radiative Recombination Processes in Halide Perovskites Observed by Light Emission Voltage Modulated Spectroscopy

et al. 2023

View full text Add to dashboard Cite

and discharge of the carriers at the contact layers; [12,[25][26][27] however, these phenomena are currently not very well understood.The light emission kinetics in perovskite LEDs and in organic light-emitting diodes (OLEDs) is usually investigated using a range of steady-state and timeresolved methods. [26,28] Remarkably, frequency-resolved methods such as impedance spectroscopy (IS) are highly effective for the separation of concomitant kinetic phenomena. [29] The connection between time transients and light-stimulated frequency methods in halide perovskite has been reviewed recently. [30] Here, we explore a new experimental measuring technique that can provide significant information about recombination in high-performance solar cells and LEDs. We analyze the frequency-resolved light emission with respect to an applied modu lated voltage, that we denote light emission voltage modulated spectroscopy (LEVS). The main point of this investigation is to reveal significant features of the radiative charge recombination that are difficult to be discerned in other measurement techniques. [30] This methodology will be especially useful when the radiative recombination event is convoluted with previous electronic carrier steps such as transport, trapping, or contact polarization effects, and/or ionic-related phenomena. It has previously been remarked that the capacitance and luminance of LEDs show correlated features [21,31,32] and some studies of electrically stimulated light emission spectroscopy have been reported, [33][34][35] but unfortunately, a general methodology has not been fully developed.Here we describe the first LEVS experiments in halide perovskite LEDs and establish an equivalent circuit model to understand the observed spectra, based on the previous experience in IS. We show that the method provides unique information on the recombination processes that cannot be accessed by purely electrical techniques, thus highlighting the interest of this new experimental technique for the characterization of optoelectronic devices, especially those presenting multiple physical phenomena, as it is the case of halide perovskite-based systems. The Transfer Functions of Frequency Resolved Measurements IS is a general-purpose characterization technique that is used in a large variety of fields to extract dynamic information on anyThe kinetics of light emission in halide perovskite light-emitting diodes (LEDs) and solar cells is composed of a radiative recombination of voltage-injected carriers mediated by additional steps such as carrier trapping, redistribution of injected carriers, and photon recycling that affect the observed luminescence decays. These processes are investigated in high-performance halide perovskite LEDs, with external quantum efficiency (EQE) and luminance values higher than 20% and 80 000 Cd m −2 , by measuring the frequency-resolved emitted light with respect to modulated voltage through a new methodology termed light emission voltage modulated spectroscopy (LEVS). The spectra are shown to provid...

show abstract

Section: Discussionmentioning

confidence: 99%

Radiative Recombination Processes in Halide Perovskites Observed by Light Emission Voltage Modulated Spectroscopy

et al. 2023

View full text Add to dashboard Cite

show abstract

“…Thermally evaporated thin films of LiF are known to be more sensitive to radiation damage compared with the bulk crystals [18]. Such films are known to consist of nanoparticles that coalesce into larger crystals above a critical thickness [33,34]. Due to the small size of the LiF nanoparticles on the DIP film, and their incomplete coverage on the DIP surface, it is likely that this prolonged exposure, even with a relatively small dose of energy, was sufficient to radically alter the LiF particles, generating fluorine in excited states or secondary photons that can affect the underlying DIP film.…”

Section: Discussionmentioning

confidence: 99%

“…Thermally evaporated LiF has a granular and porous morphology, consisting of crystallites that are nearly an order of magnitude larger than the nominal deposited thickness [33,34] as well as high surface roughness [19,33,35]. Structurally, LiF thin films on many surfaces are similar to their bulk crystallographic structure, typically forming a textured polycrystalline arrangement with either the (1 1 1) or (1 0 0) planes lying nearly perpendicular to the substrate surface depending on the substrate temperature [36,37], and on the substrate [34].…”

Section: Introductionmentioning

confidence: 99%

“…Structurally, LiF thin films on many surfaces are similar to their bulk crystallographic structure, typically forming a textured polycrystalline arrangement with either the (1 1 1) or (1 0 0) planes lying nearly perpendicular to the substrate surface depending on the substrate temperature [36,37], and on the substrate [34]. When deposited on organic surfaces, the low sticking coefficient results in the formation of disconnected nanoparticles roughly 0.5 nm in diameter [33,34].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

LiF Nanoparticles Enhance Targeted Degradation of Organic Material under Low Dose X-ray Irradiation

Maye

Turak

2021

Radiation

Self Cite

View full text Add to dashboard Cite

The targeted irradiation of structures by X-rays has seen application in a variety of fields. Herein, the use of 5–10 nm LiF nanoparticles to locally enhance the degradation of an organic thin film, diindenoperylene, under hard X-ray irradiation, at relatively low ionizing radiation doses, is shown. X-ray reflectivity analysis indicated that the film thickness increased 12.04 Å in air and 11.34 Å in a helium atmosphere, under a radiation dose of ∼65 J/cm2 for 3 h illumination with a bi-layer structure that contained submonolayer coverage of thermally evaporated LiF. This was accompanied by significant modification of the surface topography for the organic film, which initially formed large flat islands. Accelerated aging experiments suggested that localized heating was not a major mechanism for the observed changes, suggesting a photochemical mechanism due to the formation of reactive species from LiF under irradiation. As LiF has a tendency to form active defects under radiation across the energy spectrum, this could could open a new direction to explore the efficacy of LiF or similar optically active materials that form electrically active defects under irradiation in various applications that could benefit from enhanced activity, such as radiography or targeted X-ray irradiation therapies.

show abstract

“…36 The electron injection barrier can be markedly decreased by inserting the LiF layer under forward applied bias. 37,38 The J-V curves of PM-APDs with 1 nm LiF as the interfacial layer were tested in the dark and under white light-illumination with the intensity of 1 mW cm À2 , shown in Fig. S4 (ESI †).…”

Section: Eqementioning

confidence: 99%

Highly sensitive broadband photomultiplication type all-polymer photodetectors and their applications in optical pulse counting

et al. 2022

View full text Add to dashboard Cite

show abstract

Necessity of submonolayer LiF anode interlayers for improved device performance in blue phosphorescent OLEDs

Cited by 10 publications

References 71 publications

Radiative Recombination Processes in Halide Perovskites Observed by Light Emission Voltage Modulated Spectroscopy

Radiative Recombination Processes in Halide Perovskites Observed by Light Emission Voltage Modulated Spectroscopy

LiF Nanoparticles Enhance Targeted Degradation of Organic Material under Low Dose X-ray Irradiation

Highly sensitive broadband photomultiplication type all-polymer photodetectors and their applications in optical pulse counting

Contact Info

Product

Resources

About