Electroluminescence Emission Research Articles

Efficient non-doped cluster light-emitting diodes based on semiconducting copper iodide hybrids

Copper iodide hybrid clusters have attracted lots of interest in solution-processed light-emitting diodes (LEDs) for solid-state lighting and display in recent years, benefiting from their simple synthesis, structural diversity, high photoluminescence quantum yield (PLQY), and non-toxicity. However, most efficient copper iodide cluster LEDs are made by host-guest doped emitters and thus suffer from cumbersome synthesis and increased costs from the expensive hosts. Here, we report a non-doped cluster LED based on a novel copper iodine hybrid [35DPPy]4Cu2I2 (35DPPy: 3,5-diphenylpyridine) with high PLQY and decent charge transport characteristic. The non-doped [35DPPy]4Cu2I2 film synthesized by a one-step spin-coating approach possess the flat and compact morphology, high PLQY of 59.6%, and excellent heat/ultraviolet (UV) light/moisture/oxygen stability. The efficient green PL of [35DPPy]4Cu2I2 is proved to originate from the synergistic contribution from thermally activated delayed fluorescence and phosphorescence. A non-doped green LED based on [35DPPy]4Cu2I2 emitters is fabricated, achieving a peak external quantum efficiency of 4.8% and a maximum luminance of 3895 cd/m2. More importantly, large-area LEDs with an emitting area of 4.00 cm2 are realized with homogeneous and bright electroluminescence, showing their attractive potentials as novel electroluminescent emitters in the application of non-doped cluster LEDs.

Structural and optical properties of position-controlled n-ZnO nanowire arrays: Potential applications in optoelectronics

Highly position-controlled ZnO nanowire (NW) arrays and nanowire-cluster (NW–C) arrays are grown on mask-patterned gallium nitride (GaN) substrates by hydrothermal method. Electroluminescence (EL) emissions with blue-violet light at forward-bias(fb) voltage, EL emissions with yellow light at reverse-bias(rb) voltage, and EL emission at both rb voltages and rb voltages were achieved by the adjustment of the size of the heterojunction interface between wire arrays and film. The high rb current is attributed to electron tunneling transport edge effect via a narrow tunnel barrier. The obtained results highlight that the EL characteristics of ZnO NWs can be tuned and controlled through the size of the heterojunction interface between wire arrays and film. Besides, the nonplanar heterogeneous structure of ZnO NW arrays/GaN film also shown a great spectral response characteristic in the ultraviolet(UV) band, which proves that the structure of is worthy of being studied to achieve high performance UV photodetectors.

Modified surface ligand management of CsPbI3 perovskite quantum dots enables efficient and stable electroluminescent solar cells

Solution-processed CsPbI3 perovskite quantum dots (PQDs) have attracted enormous attention in both photovoltaic and electroluminescent applications in recent years. However, the surface defects of CsPbI3 PQDs in the ligand exchange procedure still suffer the challenge of imperfect passivation, leading to poor device performance and ambient stability. In this work, we propose a modified surface ligand management to deposit CsPbI3 PQD films using a layer-by-layer (LBL) solid-state exchange strategy, and its applications in photovoltaic and electroluminescent devices are studied. The conjugated phenethylammonium iodide (PEAI) ligand, acting as a short-chain ligand with a phenyl group (PEA+ ion) for encapsulating the CsPbI3 PQDs during the LBL procedure, which can both realize enhanced inter-dot coupling and defects passivation compared with conventional post-treatments. We further demonstrate the balanced transport and injection of electrons and holes within the PEAI-LBL based CsPbI3 PQD films. With this approach, the CsPbI3 PQD solar cells based on PEAI-LBL yielded a champion power conversion efficiency (PCE) of up to 14.18% with a high open voltage of 1.23 V, along with obviously electroluminescent red emission properties in one device. Meanwhile, the unencapsulated devices exhibited excellent stability under a high-humidity environment. This strategy should accelerate advancement in utilizing PQDs for bifunctional optoelectronic applications.

Boron-, sulfur- and nitrogen-doped decacyclic multiple resonance emitters for narrowband deep blue electroluminescence

Two boron-, sulfur- and nitrogen-doped polycyclic aromatic hydrocarbon (PAH) multiple resonance (MR) emitters, namely mDBNS and mDBNStBu, are developed by introducing two pairs of boron (B) and sulfur (S) atoms at meta-positions of central benzene and one carbazole moiety in decacyclic aromatic skeletons. The resultant emitters exhibit efficient deep blue narrowband emission at 451–457 nm with full width at half maximum (FWHM) of 18–22 nm in toluene, together with PLQY of 70%–76% and reverse intersystem crossing rate (kRISC) of 1.1–1.2 × 105 s−1. Solution-processed organic light-emitting diodes (OLEDs) employing mDBNStBu as emitters exhibit deep blue electroluminescence at 462 nm with CIE coordinates of (0.13, 0.12), together with a maximum external quantum efficiency (EQEmax) of 10.4%.

Correlation Measurements for Carbon Nanotubes with Quantum Defects.

Single-photon sources are essential building blocks for the development of photonic quantum technology. Regarding potential practical application, an on-demand electrically driven quantum-light emitter on a chip is notably crucial for photonic integrated circuits. Here, we propose functionalized single-walled carbon nanotube field-effect transistors as a promising solid-state quantum-light source by demonstrating photon antibunching behavior via electrical excitation. The sp3 quantum defects were formed on the surface of (7, 5) carbon nanotubes by 3,5-dichlorophenyl functionalization, and individual carbon nanotubes were wired to graphene electrode pairs. Filtered electroluminescent defect-state emission at 77 K was coupled into a Hanbury Brown and Twiss experiment setup, and single-photon emission was observed by performing second-order correlation function measurements. We discuss the dependence of the intensity correlation measurement on electrical power and emission wavelength, highlighting the challenges of performing such measurements while simultaneously analyzing acquired data. Our results indicate a route toward room-temperature electrically triggered single-photon emission.

Synthesis and characterization of a blue host polymer incorporating a chrysene moiety for solution-processed OLEDs

We synthesized two blue fluorescent materials, 6-(3-vinylphenyl)chrysene (St-C) and 6,12-bis(3-vinylphenyl)chrysene (St-C-St), for the first time, incorporating styrene into a chrysene core. These materials were polymerized via radical polymerization, resulting in the formation of polymeric blue-emitting materials, Poly 6-(3-vinylphenyl)chrysene (Poly St-C) and Poly 6,12-bis(3-vinylphenyl)chrysene (Poly St-C-St). Poly St-C exhibited deep blue emission at 395 nm in solution state. We fabricated Organic Light-Emitting Diode (OLED) devices, employing Poly St-C as the host material and 6,12-bis[4-(diphenylamino)phenyl]chrysene (TPA-C-TPA) as the dopant. The OLED device displayed electroluminescence (EL) emission in the deep blue region and achieved Commission Internationale de l‘Éclairage (CIE) coordinates of (0.157, 0.078).

Er‐Doped MgAl2O4 Nanofilms Enabling Highly Efficient Near‐Infrared Electroluminescence from the Silicon‐Based MOS Devices Fabricated by Atomic Layer Deposition

AbstractEr3+‐doped polycrystalline MgAl2O4 (MAO:Er) spinel nanofilms are deposited via atomic layer deposition, and the metal‐oxide–semiconductor light emitting devices are fabricated. The crystallinity and morphology of the MAO:Er nanofilms are explored by modifying the annealing temperatures, Al2O3/MgO ratios and Er2O3 dopant cycles. The similar electroluminescence (EL) emissions peaking at 1530 nm indicates the identical crystal field environment for the doped Er3+ ions. The concentration quenching is verified to occurs via the energy transfer among the neighboring Er3+ ions. The optimal device (800 °C‐annealed, Al2O3/MgO ratio close to stoichiometry, Er3+: 1.85 mol%) yields the highest external quantum efficiency of 28%, the power efficiency of 0.32% and the optical power density of 14.62 mW cm−2. The smooth MAO:Er spinel nanofilms with the low refractive index and high resistance ensure the highly efficient light extraction and the generation of energetic electrons for the impact excitation of Er3+ ions. The trap‐assisted tunneling under operation electric field dominates the conduction mechanism for the EL emissions. The estimated decay lifetime of 1154.4 µs and a large‐stimulated emission cross‐section in the order of 10−15–10−14 cm2 are revealed from the EL emissions. Intense near‐infrared emissions from these Si‐based MAO:Er devices have great potential in the optoelectronic applications.

Functionalization of the Octahydro-Binaphthol Skeleton: A Universal Strategy for Directly Constructing D-A Type Axially Chiral Biphenyl Luminescent Molecules.

D-A type axially chiral biphenyl luminescent molecules are directly constructed through ingenious functionalization of the octahydro-binaphthol skeleton without optical resolution. The circularly polarized organic light-emitting diodes based on them display remarkable circularly polarized electroluminescence emission, a high luminance of >10 000 cd m-2, a maximum external quantum efficiency of 6.6%, and an extremely low-efficiency roll-off. This work provides a universal strategy for developing efficient and diverse axially chiral biphenyl emitters.

Monolayer WS2 electro- and photo-luminescence enhancement by TFSI treatment

Layered material heterostructures (LMHs) can be used to fabricate electroluminescent devices operating in the visible spectral region. A major advantage of LMH-based light emitting diodes (LEDs) is that electroluminescence (EL) emission can be tuned across that of different exciton complexes (e.g. biexcitons, trions, quintons) by controlling the charge density. However, these devices have an EL quantum efficiency as low as ∼10−4%. Here, we show that the superacid bis-(triuoromethane)sulfonimide (TFSI) treatment of monolayer WS2-LEDs boosts EL quantum efficiency by over one order of magnitude at room temperature. Non-treated devices emit light mainly from negatively charged excitons, while the emission in treated ones predominantly involves radiative recombination of neutral excitons. This paves the way to tunable and efficient LMH-based LEDs.

Synthesis and optical properties of dithieno-1,4-thiaborins bearing electron-donating amino groups

Abstract Dibenzo-1,4-heteraborins and their π-extended derivatives have been paid increased attention to because of their potential as optical and electronic functional materials such as organic electroluminescence emitters. However, 1,4-heteraborin compounds with heteroaromatic ring systems remain scarce, even though Liu et al. recently reported the synthesis, properties, and functionalization of dithieno-1,4-thiaborins (DTTBs). In this work, DTTBs with 10H-phenothiazine-10-yl (Pz), 9H-carbazol-9-yl (Cz), and p-(Ph2N)C6H4 groups as electron-donating amino groups at the α-positions of their thiophene moieties were synthesized using palladium-catalyzed coupling reactions. X-ray crystallographic analysis revealed the molecular structure of a DTTB substituted with Pz groups. This analysis showed that the 2 Pz moieties adopted extra (quasi-axial) conformations. The Cz- and p-(Ph2N)C6H4-substituted DTTBs showed red-shifted absorption and emission when compared to the original DTTBs. This shift is due to donor–acceptor interactions between the amino groups and the DTTB cores. The Pz-substituted DTTB exhibited dual fluorescence emissions, originating from the locally excited (LE) and twisted intramolecular charge transfer (TICT) states. The intensity and nature of these emissions varied based on solvent polarity, temperature, and viscosity, suggesting the potential of the Pz-substituted DTTB to act as a fluorescent environment sensor.

Spectrally Stable Deep-Blue Light-Emitting Diodes Based on Layer-Transferred Single-Crystalline Ruddlesden-Popper Halide Perovskites.

A novel approach to producing high-color-purity blue-light-emitting diodes based on single-crystalline Ruddlesden-Popper perovskites (RPPs) is reported. The utilization of a pure bromide composition eliminates any possibility of halide segregation, which can otherwise lead to undesired shifts in the emission wavelength or irreversible degradation of the spectral line width. Phase-pure PEA2MAPb2Br7 single crystals with a lateral size exceeding 1 cm2 can be synthesized using the inverse temperature crystallization method. To prepare RPP layers with a thickness of less than 50 nm, we employ a thinning process of the initially thick bulk crystals, followed by a dry-transfer process to place them onto a hole transport layer and an indium-tin-oxide-coated glass substrate. By utilizing polydimethylsiloxane as a handling layer, deformations of the bulk RPP crystal and exfoliated RPP layer, as well as the formation of defects such as pinholes, can be effectively suppressed. Subsequent depositions of an electron transport layer and a metal contact complete the fabrication of electroluminescence (EL) devices. The EL devices utilizing the single-crystalline RPP demonstrate excellent spectral stability across a broad range of the applied bias voltage spanning from 4.5 to 10 V, exhibiting a significantly narrow line width of 14 nm at an emission wavelength of 440 nm that can potentially cover 99.3% of the Rec. 2020 color gamut. The sharp EL emission spectrum can be effectively preserved, avoiding any broadening of the line width, by suppressing Joule heating throughout the device operation, in addition to the intrinsic stability of single-crystalline RPPs.

Encapsulation of Er-doped GeO2 nanofilms by Al2O3 atomic layers: Surficial sensitivity to trimethylaluminum and improvement on electroluminescence

Based on previous results of the Er-doped GeO2 nanofilms fabricated by atomic layer deposition (ALD), the interfacial reactions of Al2O3 precursor within the GeO2/Al2O3:Er nanolaminates are investigated. The ALD pulse of Al(CH3)3 etches the as-deposited GeO2 nanofilm, while the oxidation of Al(CH3)3 by ozone realizes the deposition of atomic Al2O3 layer onto GeO2 surface. The Al2O3 atomic layers with ≥4 ALD cycles improve the thermal stability of the ALD GeO2 nanofilms, which restrain the formation of nanograins and also the reduction of film thickness during high-temperature annealing, giving rise to smooth GeO2/Al2O3:Er nanolaminates. For the 1530 nm electroluminescence (EL) from the silicon-based devices fabricated using the GeO2/Al2O3:Er nanolaminates annealed at 800 °C, the excitation efficiency is tripled to 22.1 %. The conduction of the energetic electrons resulting in the EL emissions still confirms to the trap-assisted tunneling mechanism within these amorphous GeO2/Al2O3:Er nanolaminates. The prototype devices based on the Al2O3-inserted nanolaminates exhibit comparatively increased operation time. These GeO2/Al2O3:Er nanolaminates with enhanced stability and improved optoelectronics performance pave the way for the practical utilization of ALD GeO2 nanofilms.

Optical Filter Design for Daylight Outdoor Electroluminescence Imaging of PV Modules

This paper presents an advanced outdoor electroluminescence (EL) imaging system for inspecting solar photovoltaic (PV) modules under varying daylight conditions. EL imaging, known for its effectiveness in non-destructively detecting PV module defects, is enhanced through specialized optical filters. These filters, including a bandpass filter targeting EL emissions and a neutral density filter to reduce background light, significantly improve the system’s signal-to-noise ratio (SNR). The experimental results demonstrate the system’s enhanced performance, with superior clarity and detail in EL emissions, enabling precise defect localization and characterization at the cellular level. Notably, the system achieves an SNR improvement, with values consistently above two, outperforming previous systems and confirming its suitability for efficient solar PV maintenance and diagnostics. This research offers a flexible approach to optimizing EL imaging quality across various solar irradiance levels and angles, essential for improved PV module performance and reliability. The system effectively handles different PV module configurations, orientations, and types, including monofacial and bifacial arrays. It showcases robust imaging capabilities under high solar irradiance and different sun illumination levels, maintaining high-quality imaging due to its optimized filter design. Additionally, the system’s adaptability in detecting EL emissions from series-connected PV modules is highlighted, demonstrating its comprehensive evaluation capabilities for PV array performance.

Selective syntheses of homoleptic Ir(iii) complexes bearing di-CF3-functionalized benzoimidazol-2-ylidenes for generation of blue phosphorescence

Di-CF3-functionalized benzo[d]imidazol-3-ium pro-chelates were employed in the selective syntheses of fac-coordinated Ir(iii) carbene emitters for efficient blue electroluminescence and hyperphosphorescence.

Asymmetric multiple resonance thermally activated delayed fluorescence emitters for sky-blue and pure blue electroluminescence

Two asymmetric MR-TADF materials, Cz-SCz and BCz-SCz, exhibit sky-blue and pure blue emission with small FWHMs of 28 and 24 nm, respectively. OLEDs display EQEmax values of up to 20.5%, and that with BCz-SCz achieves pure blue emission with a CIEy coordinate below 0.15.

Donor engineering to regulate fluorescence of a symmetrical structure based on a fluorene bridge for white light emission.

A white organic light-emitting device (WOLED) obtained using blue and yellow complementary colors possesses extremely high optical efficiency. We designed and prepared a completely symmetric D-π-D type efficient blue light small molecule FFA based on octylfluorene as a π bridge, where the undoped device showed efficient blue organic light-emitting device (OLED) performance with a maximum emission wavelength of 428 nm, Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.11) and one of the narrowest full width at half maximum (FWHM) of 35 nm. To improve the matching measure of complementary color materials for achieving white light emission, a yellow light small molecule FCzA was prepared by adjusting the conjugation degree of peripheral electron-donating groups based on the same fluorene-based π bridge with FFA. Undoped devices based on FCzA demonstrated an electroluminescence (EL) emission peak at 576 nm with CIE coordinates of (0.43, 0.49) and a relatively wide FWHM of 130 nm. Ultimately, the white OLED device was modulated with CIE coordinates located at (0.33, 0.38) via proportional regulation with a mixture of FFA and FCzA in a ratio of 10 : 3 as the light-emitting layer.

Highly efficient pure organic near-ultraviolet (NUV) electro-fluorescent materials with high electron mobility and improved hole mobility.

The lack of blue-emissive materials with high efficiency and excellent color purity commonly represents a pivotal obstacle in the development of organic light-emitting diodes (OLEDs). In this work, two blue to near-ultraviolet (NUV) donor-π-acceptor (D-π-A) emitters based on a fluorene π-bridge, 9-PCZCFTZ and 3-PCZCFTZ, are thus designed and synthesized, and non-doped devices derived from these two materials exhibit electroluminescence (EL) emission peaks at 404 nm and 417 nm, respectively. Interestingly, due to the specific stacking, a phenomenon appears in both materials in which the mobility of the electron is much higher than that of the hole, prompting us to use host doping to increase the hole mobilities, which ultimately leads to excellent OLED performances. As a result, the maximum external quantum efficiency (EQEmax) values of 9-PCZCFTZ and 3-PCZCFTZ in the doped devices reach as high as 14.5% and 10.8% respectively. Notably, both OLEDs show high blue purity very close to the BT.2020 standard.

Novel broadband near-infrared emission in Cr3+-activated Sr3ZnGe5O14 phosphor for an electroluminescent stable pc-LED

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have exhibited tremendous potential in spectroscopic technology, promoting the demand of developing novel NIR materials with excellent properties. In this paper, a series of germanate based NIR phosphors Sr3ZnGe5O14: xCr3+ (0 ≤ x ≤ 0.05) were synthesized by high temperature solid state reaction. The X-ray diffraction (XRD), scanning electron microscopy (SEM), Ultraviolet diffuse reflection, photoluminescence spectra and PL decay were measured to analyze the crystal structure, morphology properties and elements composition, PL emission properties and lifetimes of these NIR phosphors. Results demonstrated that phosphors Sr3ZnGe5O14: xCr3+ (0 ≤ x ≤ 0.05) crystallized in a trigonal with a space group of P321(150) with a broad band gap (Eg) of 4.70–4.59 eV. Sample Sr3ZnGe5O14: 0.03Cr3+ with the best PL emission properties showed a good thermal stability with the PL emission intensity remains 69 % of its initial value at 420 K. It's worth noting that the NIR device based on Sr3ZnGe5O14: 0.03Cr3+ displays an impressive electroluminescent emission stability, for example, the electroluminescent emission intensity is still about 92.3 % of its initial value when the NIR pc-LED light up for 18 h. These research results provided an important guidance for developing novel Cr3+ doped germanate based NIR phosphors with excellent thermal and electroluminescent emission stability.

Unveiling the Potential of Infrared Thermography in Quantitative Investigation of Potential-Induced Degradation in Crystalline Silicon PV Module

Potential-induced degradation-shunting (PID-s) is a severe degradation mechanism in photovoltaic (PV) cells that significantly impacts module performance. Regular monitoring and quantitative assessment of PID-s are crucial for ensuring long-term reliability of PV systems. Current-voltage (I-V) characteristics and electroluminescence (EL) imaging are commonly used for quantitative performance evaluation of PID-s affected PV modules. However, conducting I-V measurements is time-consuming when performed across large PV installations, while EL imaging has limitations for severely PID-s affected cells with no EL emission. This article proposes the use of inverse infrared (IRINV) thermography as an alternative investigation technique for PID-s in a PV module. IRINV imaging is fast and also effectively maps the severely PID-s affected cells in a PV module. This article unveils the potential of IRINV thermography in quantitative investigation of PID-s in crystalline silicon PV modules. The module level investigations present insights into the correlations between cell temperature and power output under different imaging conditions using Pearson correlation. Results indicate that steady-state operation with medium input current provides the most suitable condition for quantitative PID-s investigation. Furthermore, cell level analysis of temperature distribution and its variation with PID-s progression has been investigated using histogram and kernel density estimation (KDE) statistical tools, revealing distinct patterns as PID-s progresses. A PID-s severity index is proposed based on KDE, providing a quantitative measure of PID-s severity in cells within a PV module. This work provides valuable insights into the use of IRINV thermography as an alternative technique for assessment of PID-s in PV module inspection.

1530-nm electroluminescence from p-Ga2S3:Er/n+-Si heterojunctions induced by Zener tunneling

Silicon-based near-infrared (NIR) light sources with a simple structure are significant for circuit integration and fiber optic communications. Herein, 1530-nm electroluminescence (EL) from p-Ga2S3:Er/n+-Si junction light-emitting devices (LEDs) is reported with Er-doped Ga2S3 nanofilms as the photoemission layer and heavily doped n-type silicon as the substrate. The 1530-nm EL emission is attributed to the energy transfer between the Ga2S3 host and the Er3+ dopant, and it reaches its maximum at Er-doping concentration of 1 mol. % as the device works at −4.8 mA. The Er-related NIR EL occurs only at reverse voltages because the holes and electrons for recombination in Ga2S3:Er come from the Zener tunneling in the depletion region and the direct ITO injection, respectively. The realization of 1530-nm p-Ga2S3:Er/n+-Si LEDs offers opportunities for silicon-based integrated light sources.