External Quantum Efficiency Values Research Articles

Improved Charge Recombination Efficiency in Organic Light‐Emitting Transistors via Luminescent Radicals

AbstractLuminescent radicals are attracting attention as emitters in electroluminescent devices thanks to the exploitation of doublet excitons. Recent studies reveal that exciton formation in radical organic light‐emitting diodes (OLEDs) primarily occurs through a charge trapping mechanism. Although typically detrimental for OLEDs, this might be a key process to elucidate light emission in organic light‐emitting transistors (OLETs). Here, a unipolar n‐type architecture suitable for the implementation of radical emitters is introduced, designed based on computational calculations. The operation of the as‐realized devices incorporating the newly synthesized [2,6‐dichloro‐4‐(2,6‐dimethoxyphenyl)phenyl](3,5‐dichloro‐4‐pyridyl) (2,4,6‐trichlorophenyl)methyl radical is investigated via transient electroluminescence measurements to demonstrate the occurrence of long‐living emission ascribed to the charge trapping mechanisms. Moreover, a comprehensive understanding of the processes governing radical‐OLET is obtained by recording complete 2D maps of both optical and electrical response of the device as a function of applied voltages. Notably, the trapping of electrons by radical moieties is demonstrated to generate a negative charge density in the emissive layer that facilitates holes to be injected: increasing the balance of opposite charge carriers, a tenfold enhancement of the external quantum efficiency (EQE) at the proper source‐drain and source‐gate voltage conditions is reported to reach a maximum EQE value of 0.2%.

Narrowband Emission in Pt(II) Complexes via Ligand Engineering for Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractIn this study, three stable tetradentate Pt(II) complexes are synthesized and characterized, namely, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu, tailored for blue phosphorescent organic light‐emitting diodes to realize high‐efficiency and narrowband emissions via ligand engineering. Biphenyl (Pt‐biPh) or tert‐butyl‐modified biphenyl (Pt‐biPh5tBu and Pt‐biPh4tBu) is introduced into the carbene unit of the ligand to control the intermolecular interactions between the Pt(II) phosphors. Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu exhibit high photoluminescence quantum yields of 74%, 84%, and 92% with exciton lifetimes of 2.2, 2.3, and 2.5 µs, respectively, demonstrating rapid and efficient light emission. Furthermore, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu show maximum external quantum efficiency (EQE) values of 18.1%, 19.0%, and 21.8%, respectively. Pt‐biPh5tBu and Pt‐biPh4tBu exhibit narrowband emission with a full width at half maximum of 21 nm owing to the small vibrational emission because of their sterically hindered and bulky ligand structures. Moreover, phosphor‐sensitized thermally activated delayed fluorescence devices employing a Pt‐biPh4tBu sensitizer achieve a high EQE of 28.6%. In particular, Pt‐biPh4tBu performs better than the state‐of‐the‐art phosphor as the sensitizer of the blue phosphor‐sensitized thermally activated delayed fluorescence devices in terms of the EQE.

Construction of Concentration Quenching‐Resistant Multi‐Resonance TADF Emitters via Positional Isomerization for OLEDs

AbstractMultiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters are promising for high‐definition organic light‐emitting diodes (OLEDs) due to their high exciton utilization and color purity. However, strong interchromophore interactions cause most MR‐TADF emitters with planar structures to aggregate at high doping concentrations, leading to degraded efficiencies. Herein, using benzenesulfonyl‐functionalized dibenzothiophene sulfoximine with steric effects, three MR‐TADF emitters (2SBN, 3SBN, and 4SBN) are synthesized by coupling the classic DtBuCzB skeleton at different sites. Three emitters exhibit green or blue‐green emission with full width at half maximum (FWHM) values less than 29 nm and photoluminescence quantum yields exceeding 90%. OLEDs based on 2SBN, 3SBN, and 4SBN achieve high maximum external quantum efficiency (EQEmax) values of 30.1%, 27%, and 33.8%, respectively, at a 5 wt.% doping concentration. Notably, due to the distorted conformation of 4SBN and suppressed intermolecular interaction, the OLED remains high EQEmax of 28.9% at a doping concentration of 20 wt.%. These results demonstrate the feasibility of molecular design to modulate spatial conformations via positional isomerism to develop MR‐TADF emitters with reduced concentration quenching.

Synthesis, Photoluminescence, and Electroluminescence of Phosphorescent Dipyrido[3,2-a;2'3'-c]phenazine-Platinum(II) Complexes Bearing Hole-Transporting Acetylide Ligands.

In this study, novel phosphorescent dipyrido[3,2-a;2'3'-c]phenazine (dppz)-platinum(II)-phenylacetylide complexes were developed to fabricate non-doped organic light-emitting diodes (OLED) by solution-processing. To facilitate the charge carrier injection into the emitting layer (EML), 3,6-di-tert-butylcarbazole-functinalized phenylacetylides were employed. As for the dppz ligand, 9,9-dihexylfluoren-2-yl and 4-hexylthiophen-2-yl side-arms were introduced to the 2,7-positions, which led to reddish orange and red photoluminescence (PL), respectively, in solution and film states (PL wavelength: ca. 600 and ca. 625 nm, respectively). The carbazole-appended phenylacetylide ligands hardly affected the emission color, although unsubstituted phenylacetylides gave rise to aggregate- or excimer-based near-infrared PL with a low quantum yield. Two types of non-doped OLEDs were fabricated: single-layer and multilayer devices. In both devices, the organic layers were fabricated by spin-coating, and the EML consisted of a neat film of the corresponding platinum(II) complex. Therein, electroluminescence spectra corresponding to those of PL were observed. The single-layer devices exhibited low device efficiencies due to a deteriorated charge carrier balance. The multilayer devices possessed hole- and electron-transporting layers on the anode and cathode sides of the EML, respectively. Owing to an improved charge carrier balance, the multilayer devices exhibited higher device performance, affording considerably improved values of luminance and external quantum efficiency.

Enhanced Quantum Efficiency of Near-IR Perovskite Light Emitting Diodes Via Dual Interfacial Modification

Near-infrared (NIR) light-emitting diodes play a crucial role in a wide range of applications, including sensors, night vision displays, security systems, medicine, spectroscopy, and military applications. The potential for high-performance NIR perovskite light-emitting diodes (NIR-PeLEDs) has been highlighted with the impressive advancement of fluorescent perovskite thin films. These PeLEDs exhibit promising features such as a tunable band gap, high color purity, and low non-radiative recombination rates. Despite these advantages, the current state-of-the-art NIR-PeLEDs faces challenges primarily related to poor film quality and increased defect states, leading to limitations in external quantum efficiency (EQE) and operational stability. In addressing these issues, we present a novel dual interfacial modification approach involving the incorporation of fluorinated phenethylammonium iodide (F-PEAI), a bulky organic cation, at both the bottom and top interfaces of perovskite emitting films. The modified interfaces result in perovskite films with a smoother surface morphology, complete coverage, and high crystallinity, leading to a red-shifted fluorescence band extending toward 800 nm. Furthermore, the introduction of F-PEAI facilitates the formation of compact and fine grains in perovskite films, contributing to an enhanced photoluminescence quantum yield (PLQY). Consequently, NIR-PeLEDs modified with F-PEAI demonstrate improved EQE values coupled with enhanced operational stability. The combination of electrical, optical, and physical analyses of both films and devices underscores the effectiveness of the dual interface modification in developing efficient NIR perovskite LEDs suitable for practical applications.

Peripheral carbazole units-decorated MR emitter containing B−N covalent bond for highly efficient green OLEDs with low roll-off

Boron−nitrogen doped multiple resonance (BN-MR) emitters, characterized by B−N covalent bonds, offer distinctive advantages as pivotal building blocks for facile access to novel MR emitters featuring narrowband spectra and high efficiency. However, there remains a scarcity of exploration concerning synthetic methods and structural derivations to expand the library of novel BN-MR emitters. Herein, we present the synthesis of a BN-MR emitter, tCz[B−N]N, through a one-pot borylation reaction directed by the amine group, achieving an impressive yield of 94%. The emitter is decorated by incorporating two 3,6-di-t-butylcarbazole (tCz) units into a B−N covalent bond doped BN-MR parent molecule via para-C−π−D and para-N−π−D conjugations. This peripheral decoration strategy enhances the reverse intersystem crossing process and shifts the emission band towards the pure green region, peaking at 526 nm with a narrowband full-width at half maximum (FWHM) of 41 nm. Consequently, organic light emitting diodes (OLEDs) employing this emitter achieved a maximum external quantum efficiency (EQEmax) value of 27.7%, with minimal efficiency roll-off. Even at a practical luminance of 1000 cd∙m−2, the device maintains a high EQE value of 24.6%.

Comprehensive investigation on ruthenium doped Sn2S3 thin films for photo sensing applications

This study investigates the deposition of tin trisulfide (Sn2S3) films onto glass substrates through the nebulizer spray technique, employing aqueous solutions of SnCl2 and SC (NH2)2 at a molar ratio of Sn to S of 1:2 under various doping concentrations of ruthenium (1, 2, 3, 4, and 5 wt %). The crystallography, morphology, chemical, optical and photo sensing characteristics of deposited thin films has been comprehensively analysed using an X-ray diffractometer, Field emission scanning electron microscope annexed with energy dispersive X-ray analyser, UV-VIS spectrometer, Photoluminescence spectroscopy and a digital Keithley source meter. The X-ray diffraction investigation clearly establishes the polycrystalline nature of the films possessing orthorhombic crystal structure. The surface morphology was visualized via Field Emission Scanning Electron Microscope which confirmed the existence of spherical nano grains at 3 % Ru doping concentration. The energy dispersive X-ray analyser spectrum was used to probe the elements present in the prepared thin film and it supports the presence of Sn, S and Ru. The optical absorption and transmittance spectra were observed in the wavelength range between 450 and 900 nm for all the samples. Enhanced absorption in the visible region is observed from the absorption spectra. Direct allowed band gap values ranging around 2.05 eV–1.92 eV is observed for these Ru doped spray pyrolyzed Sn2S3 thin films. The I–V characteristics of the samples, studied under both light and dark conditions, demonstrate an increase in current values with higher concentrations of Ru doping. The highest value of the photo current (36 μA) was observed for 3 wt % ruthenium doped film. Highest responsivity of 67.6 × 10−2 A/W was observed for 3 % Ru doped Sn2S3 film. The same sample showed a highest detectivity and external quantum efficiency values of 8.70 × 109 Jones and 157 % respectively. The quick response of the detector can be affirmed from the short rise and fall time of 1.22 s and 1.21 s, respectively. Therefore, the Sn2S3 material doped with 3 % ruthenium, produced via the current economical method, emerges as a promising candidate for application in photo-detectors.

Effects of carbazolyl and diphenylamino substituents bearing methoxy groups on the performance of hole-transporting materials in OLEDs

Newly designed and synthesized derivatives of pentaphenylbenzene with methoxy-substituted carbazolyl or diphenylamino moieties were investigated to estimate their applicability as hole transport materials. Both the compounds exhibit high thermal stability. The intramolecular charge transfer is blocked for the film of the compound containing diphenylamino groups. The intermolecular charge transfer is induced in the film of carbazolyl-containing compound. The derivative of pentaphenylbenzene and diphenylamine exhibits higher hole drift mobility (2.4·10−3 cm2/V·s at the electric field of 5.5·105 V/cm) and by 0.1 eV lower ionization potential than the carbazolyl-containing compound. Both the compounds were utilized as hole-transporting materials in a series of organic light emitting diodes (OLEDs) based on of thermally activated delayed fluorescence. With the maximum values of external quantum efficiency of 25.9 % and power efficiency of 43.4 lm/W, OLEDs containing the layers of the synthesized compounds outperformed the device based on TCTA by 4 %, without the change in spectral properties. Variable angle spectroscopic ellipsometry revealed the moderate average roughness of the films of the compound deposited by the thermal vacuum evaporation technique with an arithmetic mean deviation of not more than 0.8 nm. The prominent hole transport characteristics of the compounds make them good candidates for utilization in optoelectronic devices.

Reduced graphene oxide decorated CuO@NiO nanocomposite and their improved photosensitive activity for photodetection applications

In our proposed work, pure rGO and CuO@NiO/rGO (CNR) nanocomposites (NCs) with different ratios of CuO@NiO:rGO (90:10, 75:25 and 50:50) were synthesized and explored by XRD, SEM with EDX, TEM, XPS, UV–visible, PL and utilized to measure the current – voltage characteristics under dark and illumination conditions. TEM analysis indicates ultra-thin nanosheets of rGO with lengths of several tens of micrometer and CuO@NiO particle sizes is ∼50 nm. XPS analysis showed the presence of element and chemical states for Cu, Ni, O, and C in CNR-(50:50) sample. The energy gap (Eg) of pure rGO is 3.99eV whereas the CNR for 90:10, 75:25 and 50:50 NCs energy gap (Eg) values are viz., 1.43eV, 1.41eV and 1.39eV. The diode characteristic of CNR-(50:50)/n-Si exhibit lower ideality factor (n = 1.96), higher barrier height (ΦB = 0.80eV) under illumination condition. The CNR-(50:50)/n-Si photodiode exhibits higher photosensitivity (PS), responsivity (R), External Quantum Efficiency (EQE) and detectivity (D*) values of 956.45 %, 656.29 mA/W, 367.6/1 % and 5.72 × 1012 (Jones) respectively.

Photoluminescence of Platinum(II) Complexes with Diazine-Based Ligands.

In the last past twenty years, research on luminescent platinum (II) complexes has been intensively developed for useful application such as organic light emitting diodes (OLEDs). More recently, new photoluminescent complexes based on diazine ligands (pyrimidine, pyrazine, pyridazine, quinazoline and quinoxaline) have been developed in this context. This review will summarize the photophysical properties of most of the phosphorescent diazine Pt(II) complexes described in the literature and compare the results to pyridine analogues whenever possible. Based on the emission color, and the photoluminescence quantum yield (PLQY) values, the relationship between structure modification, and photophysical properties are highlighted. Tuning of emission color, quantum yields in solution and solid state and, for some complexes, aggregation induced emission (AIE) or thermally activated delayed fluorescence (TADF) properties are described. When emitting OLEDs have been built from diazine Pt(II) complexes, the external quantum efficiency (EQE) values and luminance for different emission wavelengths and in some cases, chromaticity coordinates obtained from devices, are given. Finally, this review highlights the growing interest in studies of new luminescent diazine Pt(II) complexes for OLED applications.

Self-powered stable high-performance UV–Vis–NIR broadband photodetector based on PVP-Cobalt@Carbon nanofibers/n-GaAs heterojunction

The self-powered PVP-Co@C nanofibers/n-GaAs heterojunction photodetector (HJPD) was fabricated by electrospinning of the nanofibers onto GaAs. An excellent rectification ratio of 6.60 × 106 was obtained from I–V measurements of the device in the dark. The I–V measurements of the fabricated device under 365 nm, 395 nm and 850 nm lights, as well as I–V measurements in visible light depending on the light intensity, were performed. The HJPD demonstrated excellent photodetection performance in terms of a good responsivity of ∼225 mA W−1 (at −1.72 V) and at zero bias, an impressive detectivity of 6.28 × 1012 Jones, and a high on/off ratio of 8.38 × 105, all at 365 nm wavelength. In addition, the maximum external quantum efficiency and NPDR values were 3495% (V = −1.72 V) and 2.60 × 1010 W−1 (V = 0.0 V), respectively, while the minimum NEP value was ∼10−14 W.Hz−1/2 for 365 nm at V = 0.V volts. The HJPD also exhibited good long-term stability in air after 30 d without any encapsulation.

High performance Al/WSe2/CuO/ITO structure based broadband photodetector

This letter reports a Al/WSe2/CuO/ITO structure based broadband photodetector. The low cost spin coating technique is utilized to deposit, p-type WSe2 film and n-type CuO film. The Al contacts were deposited over WSe2 film using thermal evaporation unit. The suggested photodetector gives the broad photo response with maximum Responsivity RS (A/W) and External Quantum Efficiency (EQE) value of 3099 A/W, 3680 A/W, and 493 A/W; 1.20 × 106%, 1.52× 106% and 2.04 × 105% at 350 nm (UV), 500 nm (visible) and 950 nm (IR) under application of −2 V bias. The EQE value beyond 100% are attributed to trap assisted photomultiplication mechanism.

Estimation of Junction Temperature in Single 228 nm‐Band AlGaN Far‐Ultraviolet‐C Light‐Emitting Diode on c‐Sapphire Having 1.8 mW Power and 0.32% External Quantum Efficiency

The increasing resistance of methicillin‐resistant Staphylococcusaureus to antibiotics is a major challenge faced by mankind in thehistory of medical science and according to United Nations, 700‐000 patients worldwide die every year from an infection with multidrug‐resistant organisms (MROs). Aluminum gallium nitride‐based 228 nm Far‐ultraviolet‐C (Far‐UVC) lightsources can be safely used as a germicidal application in both manned as wellas in unmanned environments against these MROs. Previously, the 228 nm Far‐UVC light‐emitting diode (LED) with emission power of 1 mW was reported by ourgroup, however, the value of external quantum efficiency (EQE) was not reportedusing conventional thick Ni (20 nm)/Au (100 nm) p‐electrode. Herein, animproved Far‐UVC LED on c‐Sapphire is attempted using a special technique in SR4000 type of metal‐organic chemical vapor deposition reactor to control the Al composition in n‐AlGaN buffer and across the 2 inch‐wafer. As a result, the light emission power of 1.8 mW and EQE of 0.32% in 228 nm Far‐UVC LED aresuccessfully achieved using very thin p‐electrode (Ni/Au). However, arelatively high junction temperature of ≈100°C around thejunction of Far‐UVC LED is observed. Finally, some simple heat‐sink modules forheat dissipation of Far‐UVC LED panel with light power of 30 mW are implemented.

Electroconductive and photoelectric properties of Pt/(100) β-Ga2O3 Schottky barrier diode based on Czochralski grown crystal

Pt/(100) β-Ga2O3 Schottky barrier diodes were fabricated using a plate cleaved from the crystal grown by Czochralski method. Their electroconductive and photoelectric characteristics were studied. The following values were obtained: the Schottky barrier height (1.69/1.62/1.74 eV), ideality coefficient (1.09/1.14), saturation current density (9.91 × 10–15 A/cm2), diode series resistance (7.98 kΩ), and net donor concentration [(1.8–2.4) × 1018 cm–3]. The diodes demonstrate a high rectification ratio of 1010 at an applied voltage of ± 1 V and a relatively low experimental value of the leakage current density ∼10–11 A/cm2. These structures are solar-blind and also capable of operating in self-powered mode. The diodes are highly sensitive to short-wave ultraviolet radiation with a wavelength λ ≤ 265 nm. The maximum values of responsivity (20.4 A/W), external quantum efficiency (1.2 × 104%), and detectivity (9.6 × 1015 Hz0.5 × cm × W–1) of diodes were registered under exposure to irradiation at λ = 210 nm and at applied voltage of −1 V. The responsivity and external quantum efficiency values in the self-powered operation mode were 12.3 A/W and 7.2 × 103%, respectively. The diodes showed low rise and decay times in self-powered operation mode for photodiode based on Ga2O3: 14 and 30 ms, respectively.

Chiral dual-core emitters based-on through-space coupling for high-performance OLEDs with little efficiency roll-off

Through-space coupling (TSC) is the essential component of π-stacked systems and has promise in charge transport and electronic communication, which is of great significance for the construction of efficient and stable photoelectric devices. In this work, we demonstrate a chiral dual-core strategy for the design of high-performance organic circularly polarized emitters, which features of connecting two thermally activated delayed fluorescence (TADF) luminophores with chiral linkage that allows efficient TSC to occur. Using this strategy, a pair of dual-core enantiomers, R/S-DNKP, were designed and synthesized by linking two benzophenone derivatives with a 1,1′-bi-2-naphthol unit. Compared to the mono-core counterpart NKP, the dual-core emitters exhibited the photoluminescence quantum yields up to 94 %. Moreover, benefiting from their chiral helical folding configurations, the R/S-DNKP enantiomers exhibited the luminescence dissymmetry factor (|glum|) value of +2.7 × 10−3 and −2.6 × 10−3 in doped films. Notably, the electroluminescence devices based on the R/S-DNKP enantiomers achieved external quantum efficiency values of 21.5 % and 19.7 % with little roll-off. It is believed that this molecular design strategy will pave new routes for the development of high-performance chiral emitters for future organic photonic devices.

Detection performance of flower-like hydrothermally synthesized ZnO in silicon-type photodetector

Zinc oxide (ZnO) is a versatile compound or metal oxide with a wide range of applications across various industries such as electronics, optoelectronics, and gas sensors, etc. A simple hydrothermal method was used to synthesize ZnO flower-like structures in this study. The synthesized ZnO structures were analyzed by x-ray diffractometer (XRD) and scanning electron microscope (SEM). We used ZnO structures as an interfacial layer for a Schottky-type silicon-based photodetector. While Au and Al metals were employed as metallic and ohmic contacts, respectively, p-Si was utilized as a semiconductor and substrate. Thus, Au/ZnO/p-Si sandwich was successfully fabricated and tested by current–voltage (I–V) measurements under dark and various light power illumination densities from 10 mW cm−2 to 150 mW cm−2 as well as the various wavelengths in the case of same power. The I–V characteristics were used to determine the diode and photodetection parameters. The fabricated heterostructure exhibited 77.51 mA W−1 responsivity, 1.30 × 1010 Jones specific detectivity, and 26.33% external quantum efficiency (EQE) values.

Modulating the Locally Excited States with a Regulating Substituent for Highly Efficient Red/Near‐Infrared Thermally Activated Delayed Fluorescence Emitters

AbstractDeveloping highly efficient red/near‐infrared (NIR) thermally activated delayed fluorescence (TADF) materials is important for organic light‐emitting diodes (OLEDs). Here, two TADF emitters, APTT and APTI, which have the same D/A backbone but different attaching groups at acenaphtho‐[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC) core, are reported. The appended regulating groups can not only suppress the D/A rotation due to the space confinement effects but also modulate the locally excited triplet state (3LE). The improved molecular rigidity suppresses the non‐radiative process, accounting for the improved photoluminescence quantum yields (PLQYs), while the modulated 3LE promotes the reverse intersystem crossing (RISC) process due to the high utilization efficiency of triplets. Consequently, both APTT and APTI demonstrate high PLQY and fast RISC process, thereby enhancing TADF efficiency. The doped devices based on APTT and APTI achieve maximum external quantum efficiency (EQEmax) values of 20.5% and 25.4% with emission peaks at 664 and 670 nm, respectively. The non‐doped devices of APTT and APTI achieve the EQEmax of 2.8% and 2.9% with emission peaks at 788 and 794 nm, respectively. Encouragingly, the non‐doped devices of APTI have set new records for near‐infrared TADF OLEDs based on the APDC core. This study provides an efficient approach to modulating the optoelectronic properties of highly efficient NIR TADF OLEDs.

Fabrication of Bi-doped In2S3 thin films for highly sensitive UV photodetector applications

Fabrication of highly sensitive, high-speed photodetectors, especially using cost-effective and less toxic materials, has attracted continuous attention due to their outstanding advantages. In this report, we present different properties of Bi-doped (0,1, 3, and 5 wt%) In2S3 thin films for UV photodetectors. Bi-doped (0, 1, 3, and 5 wt%) In2S3 thin films were coated on glass substrates at a temperature of 350 °C using a low-cost nebulizer spray pyrolysis method. X-ray diffraction XRD analysis confirmed the cubic phase β-In2S3 for all the deposited films and high crystallinity is obtained for 1 wt% Bi-doped film. The presence of densely packed grains in 1 wt% Bi-doped In2S3 thin film and also small grains observed for undoped In2S3 sample is evident form morphology studies. Bi doping has caused an enhancement of optical absorption and incorporation of 1 wt% of Bi3+ into In2S3 has shifted the optical band gap from 2.87 to 2.78 eV. Current − Voltage characteristics and Current–Time characterization are used to know the key parameters of the photodetectors. Among all fabricated photodetectors, the In2S3 thin film doped with 1 wt% Bi showed superior photodetector performance with calculated Responsivity (R), Detectivity (D*), and External quantum efficiency (EQE) values of 0.65 AW−1, 15 × 1010 Jones, 125 % respectively. Transient photo-response analysis showed low rise and fall time of 3.21 and 3.78 s respectively for the 1 wt% Bi-doped sample. Optimally doped In2S3: Bi (1 wt%) thin film is most suited to fabricate photo sensing-based optoelectronic devices in UV region of the spectrum.

Zirconium doped indium oxide thin films as transparent electrodes for photovoltaic applications

In this work we report on ultra-thin Zirconium doped In2O3 transparent conductive films grown at room temperature via RF-Magnetron co-sputtering. Samples from 15 nm to 90 nm thick, and low Zr atomic concentration (0.6–0.9 at.%), were annealed at T = 200 °C after the deposition. The phase-transition from amorphous to crystalline, confirmed by XRD measurements, leads to an improvement of both electrical and optical properties. The thinnest film (15 nm) shows electrical resistivity as low as 5 × 10−4 Ωcm, with carrier mobility of 20 cm2V−1s−1, and optical transmittance up to 80 % in visible and near-infrared range. IZrO electrode performances were tested through external quantum efficiency (EQE) measurements on a semi-finite Silicon Heterojunction bi-facial solar cell. The EQE values for 90 nm thick film are comparable to that of standard ITO when IZrO films are implemented as front electrodes. These results suggest that ultra-thin IZrO films may be successfully used to reduce costs and the amount of Indium used in Indium-based transparent conductive oxide layers for solar cells.

Efficient OLEDs with Alleviated Efficiency Roll‐Off Based on MR‐TADF Materials Containing Indolo[3,2,1‐jk]carbazole

AbstractThe multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials can meet the requirement of a high color gamut of displays due to their narrowband emission. However, most reported organic light‐emitting diodes (OLEDs) based on MR‐TADF materials suffer from severe efficiency roll‐off. Herein, three green MR‐TADF emitters, p‐ICz‐BNCz, m‐ICz‐BNCz, and dm‐ICz‐BNCz, are obtained by introducing bulky indolo[3,2,1‐jk]carbazole (ICz) units into the classical DtBuCzB skeleton at the para or meta positions relative to the boron‐substituted phenyl ring. Compared with the para‐substitution of ICz, the meta‐substitution not only increases the reverse intersystem crossing rate constants of m‐ICz‐BNCz and dm‐ICz‐BNCz by nearly three times, but also makes their configurations more twisted. The two factors work together to improve the utilization of triplet excitons of the emitters, showing photoluminescence quantum yields exceeding 90%. As a result, the two corresponding OLEDs exhibit maximum external quantum efficiency (EQEmax) values of 28% and 32.9%, respectively, with low‐efficiency roll‐off. At the high brightness of 1000 cd m−2, the EQE values of the two devices still maintain at 19.3% and 25.0%, respectively. In addition, green emissions with Commission Internationale de l'Eclairage coordinates of (0.20, 0.70) and (0.30, 0.67) are also observed.