Photoluminescence Quantum Efficiency Research Articles

Triphenylamine-phenylimidazole based hybridized local and charge-transfer molecular as blue-green/ white light emission emitter for light-emitting diode application

In this work, a new triphenylamine-phenylimidazole derivative named (E)-N,N-diphenyl-4-(2-(4'-(1-phenyl-1H-benzo[d]imidazole-2-yl)-[1,1′-biphenyl]-4-yl)vinyl)aniline (DPAvlBPI) with hybridized local and charge-transfer (HLCT) characteristics was successfully developed. The undoped organic light-emitting diode (OLED) based on DPAvlBPI (XF-OLED) is prepared with a maximum external quantum efficiency (EQE) of 1.23 %, and the exciton utilization efficiency (EUE) can reach 41 %. The Commission Internationale de L'Eclairage (CIE) color coordinate of XF-OLED is (0.1925, 0.3975), indicating that the device is in the blue-green light region. Since the photoluminescence quantum efficiency (PLQY) of DPAvlBPI in neat film is only 0.12, the maximum brightness of the device is 545 cd m−2. However, by dispersing DPAvlBPI in silica gel at a low concentration, the PLQY can approach 1. Therefore, the DPAvlBPI-based organic/inorganic hybrid LED XF-HBLED is prepared, and the device can achieve a luminous efficacy of 18.64 lm/W and EQE of 9.98 % at an operating current of 64.90 mA. To broaden the application scope of DPAvlBPI, a “Halochromism” white light emission system based on DPAvlBPI has been prepared, and the solution type (XF-SWLED) and solid-state(XF-W2) white light emission device based on this system have been successfully realized. The luminous efficacy of XF-W2 with a CIE coordinate of (0.3205, 0.4363) can reach 14.92 lm/W with an EQE of 8.23 % under the operating current of 64.90 mA. This provides a reference for expanding the multifunctional/multi-device applications of HLCT molecules.

Centimeter-Sized Single Crystals of Tetrahedral Manganese (II) Halide Hybrids for Wide-Color Gamut Backlighting Displays.

Phosphors with narrow-band green emissions and high photoluminescent quantum efficiency (PLQY) are significantly required for backlighting displays with wider color gamut. In this work, two centimeter-sized manganese (II) halide single crystals TMG2MnCl4 and TMG2MnBr4 (TMG = 1,1,3,3-tetramethylguanidine) are synthesized, exhibiting bright narrow-band green emissions with high PLQYs up to 62% and 90%, respectively. The narrow-band green light emission is located at 520nm with a full-width at half-maximum (FWHM) of only 57nm. The photoluminescence mechanisms of two single crystals are elaborated. Two white-light-emitting diodes for backlighting displays (BD-WLEDs) based on them are fabricated, exhibiting the widest color gamut of 122% National Television Standards Committee (NTSC), and a luminous efficacy reached ≈93lmW-1 with excellent luminescence stability at high temperatures. These properties indicate the potential applications of tetrahedral manganese (II) hybrids in wide-color gamut backlighting displays.

Heterovalent Doping in CsCdCl3 Enabled Tunable Multimode Luminescence and Photochromism Toward Multilevel Anti‐Counterfeiting

AbstractIntegrating self‐trapped excitons (STEs), dopants, and defect levels in a single‐component metal halide perovskite will be of significance for tunable multimode luminescence and photochromism. Here, a platform utilizing interactions of STEs, defects, and alien dopants in CsCdCl3 by a heterovalent doping strategy is demonstrated, in which the photoluminescence quantum efficiency is improved, and more importantly, the emissions can be manipulated statically and dynamically by dopants and changing excitation wavelength/irradiation time. Meanwhile, the presence of carrier trapping and de‐trapping processes leads to bright orange–near‐infrared persistent luminescence and photochromic behaviors, which can be quickly erased by white light, enabling visual displays and codable in dark and bright dual‐fields. Inspired by these versatile optical characteristics of doped luminescent metal halides, a multilevel encryption and anti‐counterfeiting platform with the advantages of nondestructive and convenient authentication is constructed.

Controlling Nucleation and Crystal Growth Orientation via Intermediate Ion‐Complex Formation for Efficient α‐FA0.95Cs0.05PbI3 Perovskite Solar Cells

The formamidinium–cesium (FA–Cs) alloyed metal halide perovskites demonstrate superior photovoltaics device stability; however, alloying at lower Cs concentrations (≤5%) undergoes complex intermediate phase transitions that disrupt morphological and structural properties. Herein, an intermediate ion‐complex method in a bid is attempted to achieve a near‐optimal energy bandgap of 1.52 eV for α‐FAPbI3 perovskite (alloyed with 5% Cs+ cation). Upon incorporation of judicious amount of smaller and more volatile ions (such as Cl−/Br− and methylammonium [MA]+/Cs+) into the host FAPbI3 system, these ions are observed to persist in the “transitional‐phase” and “stimulate” the formation of α‐phase. Consequently, using X‐ray and photoluminescence quantum efficiency measurements, the formation of a (110)‐plane‐oriented high‐quality FA0.95Cs0.05PbI3 perovskite thin film with significantly reduced nonradiative recombination is confirmed. An area of 25 mm2 yields a power conversion efficiency (PCE) of 20.21% and a stabilized power output of 19.82%, leveraging open‐circuit voltage of 90.4% of that Shockley–Queisser limit. The devices sustain over 1000 h without any PCE degradation.

Unveiling The Role of Cu+ Doping in Rb2AgBr3 Scintillators toward Enhanced Photoluminescence Quantum Efficiency and Light Yield

AbstractDoping in luminescent metal halides has become an effective strategy for tailoring the optoelectronic properties. Herein, Cu+ is introduced into Rb2AgBr3 to design the synthesis of Rb2AgBr3:xCu+, which possess cold‐white light emission at room‐temperature without changing the spectral profiles; however, the Cu+ incorporation significantly enhances the photoluminescence quantum efficiency to 98.8% in Rb2AgBr3:0.05Cu+. Additionally, a high scintillation light yield of up to 79 250 photons MeV−1 and a low detection limit of 714.83 nGy s−1 have been achieved via this Cu+ doping engineering. X‐ray imaging with a spatial resolution of up to 5.8 lp mm−1 is further realized using a large scintillator film prepared by mixing polydimethylsiloxane with Cu+ doped Rb2AgBr3 scintillators. This study provides a Cu+ doping design principle for improving both the photoluminescence and scintillation performances of metal halides.

Advances and future perspectives in polycrystalline halide perovskite light-emitting diodes

Metal halide perovskites (MHPs) have emerged as a highly promising candidate for next-generation light-emitting materials due to their exceptional optoelectronic properties. These properties include superior color purity, high photoluminescence quantum efficiency (PLQY), and the facile tunability of bandgap through compositional and dimensional control. Particularly, polycrystalline perovskites have been introduced as the first perovskite light-emitting diodes (PeLEDs) with superior charge mobility. However, the development of efficient and stable PeLEDs, crucial for commercialization, has proven to be a significant challenge due to the low exciton binding energy (E b) and inherent defects. Nevertheless, recent achievements have demonstrated polycrystalline PeLEDs with an external quantum efficiency (EQE) surpassing 28% and a half-lifetime (T 50) exceeding 30,000 h. In this review, we present the progress of polycrystalline PeLEDs with improved efficiency (PLQY, EQE) and stability by focusing on grain size regulation, defect passivation, and dimensional control. This review offers promising strategies for realizing polycrystalline perovskite material as a light emitter, highlights limitations and provides future perspectives for advancing PeLEDs.

Mismatch of Quasi–Fermi Level Splitting and Voc in Perovskite Solar Cells

AbstractPerovskite solar cells have demonstrated low non‐radiative voltage losses and open‐circuit voltages (VOCs) that often match the internal voltage in the perovskite layer, i.e. the quasi‐Femi level splitting (QFLS). However, in many cases, the VOC differs remarkably from the internal voltage, for example in devices without perfect energy alignment. In terms of recombination losses, this loss often outweighs all non‐radiative recombination losses observed in photoluminescence quantum efficiency measurements by many orders of magnitude. As such, understanding this phenomenon is of great importance for further perovskite solar cell development and tackling stability issues. The classical theory developed for Si solar cells explains the QFLS‐VOC mismatch by considering the partial resistances/conductivities for majority and minority carriers. Here, the authors demonstrate that this generic theory applies to a variety of physical mechanisms that give rise to such a mismatch. Additionally, it is found that mobile ions can contribute to a QFLS‐VOC mismatch in realistic perovskite cells, and it is demonstrated that this can explain various key observations about light soaking and aging‐induced VOC losses. The findings in this paper shine a light on well‐debated topics in the community, identify a new degradation loss, and highlight important design principles to maximize the VOC for improved perovskite solar cells.

Type-I CdSe@CdS@ZnS Heterostructured Nanocrystals with Long Fluorescence Lifetime.

Conventional single-component quantum dots (QDs) suffer from low recombination rates of photogenerated electrons and holes, which hinders their ability to meet the requirements for LED and laser applications. Therefore, it is urgent to design multicomponent heterojunction nanocrystals with these properties. Herein, we used CdSe quantum dot nanocrystals as a typical model, which were synthesized by means of a colloidal chemistry method at high temperatures. Then, CdS with a wide band gap was used to encapsulate the CdSe QDs, forming a CdSe@CdS core@shell heterojunction. Finally, the CdSe@CdS core@shell was modified through the growth of the ZnS shell to obtain CdSe@CdS@ZnS heterojunction nanocrystal hybrids. The morphologies, phases, structures and performance characteristics of CdSe@CdS@ZnS were evaluated using various analytical techniques, including transmission electron microscopy, X-ray diffraction, UV-vis absorption spectroscopy, fluorescence spectroscopy and time-resolved transient photoluminescence spectroscopy. The results show that the energy band structure is transformed from type II to type I after the ZnS growth. The photoluminescence lifetime increases from 41.4 ns to 88.8 ns and the photoluminescence quantum efficiency reaches 17.05% compared with that of pristine CdSe QDs. This paper provides a fundamental study and a new route for studying light-emitting devices and biological imaging based on multicomponent QDs.

Optically Active A‐Shaped Cyclic Molecules Based on Planar Chiral [2.2]Paracyclophanes Emitting Bright Circularly Polarized Luminescence with High Anisotropy Factors

AbstractOptically active A‐shaped cyclic molecules are synthesized by incorporating a planar chiral [2.2]paracyclophane unit to form a helical structure. These molecules exhibit large molar absorption coefficients, moderate photoluminescence (PL) quantum efficiencies, and high circularly polarized luminescence (CPL) anisotropy factors, resulting in high CPL brightness values (BCPL values). According to the time‐dependent density functional theory (TD‐DFT) theoretical studies, extended π‐conjugated moieties act as light‐harvesting units, and emissions occur from the helical skeletons. The TD‐DFT calculations reproduce the experimentally determined absorption, PL, circular dichroism, and CPL properties of the A‐shaped cyclic molecules.

Asymmetric Ternary Spiro Phosphine Oxide Hosts for Yellow Thermally Activated Delayed Fluorescence Diodes with External Quantum Efficiency Beyond 30%

AbstractYellow thermally activated delayed fluorescence (TADF) organic light‐emitting diodes (OLEDs) are indispensable for lighting, navigation, caution, and so on; however, their development is far behind those of three‐elementary‐color and white analogs, partially because of the lack of host specificity. In this contribution, spiro[bithoxanthene] (ST) and spiro[thioxanthene‐xanthene] (STX) are used as spiro skeletons to form asymmetric ternary structures through introducing two electron‐donating tert‐butyl carbazole (tBCz) and one electron‐withdrawing diphenyl phosphine oxide (DPPO) groups on different rings. The resulting hosts named STSPOtBCz2 and STXSPOtBCz2 not only inherit the steric hindrance of their spiro skeletons, but also achieve the ambipolar characteristics. Their suitable triplet energy levels (T1) of ≈2.5 eV support efficient energy transfer to a conventional yellow TADF emitter 4CzTPNBu with the T1 of ≈2.2 eV. It is shown that compared to STSPOtBCz2 with a symmetric core, the accumulated asymmetry of the spiro skeleton and the kind, number, and position of substitution groups in STXSPOtBCz2 further suppresses the emission quenching, resulting in the state‐of‐the‐art photoluminescent and electroluminescent quantum efficiencies of 93% and 30.6%, respectively. The maximum power efficiency beyond 90 lm W−1 further demonstrates the great potential of multi‐asymmetric host systems for energy‐saving practical application.

Customizable Scintillator of Cs3 Cu2 I5 :2% In+ @Paper for Large-Area X-Ray Imaging.

High-resolution X-ray imaging is increasingly required for medical diagnosis and large-area detection. However, the issues of scattering and optical crosstalk are limiting the spatial resolution of the indirect X-ray imaging. In this study, a feasible and efficient strategy is proposed to in situ synthesize flexible Cs3 Cu2 I5 :2%In+ @paper as a superior scintillator film, which can be scaled up to an ultra-large area of 4800 cm2 . The as-obtained Cs3 Cu2 I5 :2%In+ @paper performs a fascinating photoluminescence quantum efficiency up to 88.14%, a steady state light yield of 70169 photons/MeV, and spatial resolution of 15 lpmm-1 . Moreover, the suppressed physical scattering and optical crosstalk of the corresponding film are demonstrated. Accordingly, this work explores a feasible fabrication of customizable scintillation films with large area for high-resolution X-ray detection.

Modulation of intramolecular charge transfer in D-A functionalized pyrrolopyrazine and their application in luminescent solar concentrators

In this study, we fabricated LSCs using pyrrolopyrazine-based organic fluorophore (PP2) with an intramolecular charge transfer (ICT) function and aggregation-induced emission. PP2 incorporates unique features, including an intramolecular charge transfer (ICT) function and aggregation-induced emission. The pyrrolopyrazine core of PP2 is decorated with an electron-rich dimethylamine group and two electron-poor cyano groups, enhancing its potential for light harvesting in LSC applications. In the polymethylmethacrylate (PMMA) matrix, PP2 showed strong absorption near ultraviolet (395 nm–406 nm), emitted green-colored visible light (474 nm–478 nm), and exhibited a photoluminescence quantum efficiency (PLQY) of 67%. The external photon efficiency (ηext) and internal photon efficiency (ηint) of the fabricated LSC under AM 1.5G illumination (1 sun) were 3.36% and 39.1%, respectively. Subsequently, we conducted an analytical simulation to estimate the ηext and the ηint as the dimensions of the LSC were scaled up. In addition, the photovoltaic performance measurement under 1 sun showed a power conversion efficiency (ηPCE) of 1.074% with a scattering background and 0.633% without a scattering background. Thus, this research introduces PP2 as a novel fluorophore with promising prospects for advancing the field of LSC technology.

Controlled Photoluminescence Lifetimes and Quantum Efficiencies in Mn-Doped Two-Dimensional Perovskite via A-Site Cation Engineering

Controlled Photoluminescence Lifetimes and Quantum Efficiencies in Mn-Doped Two-Dimensional Perovskite via A-Site Cation Engineering

Valence conversion and site reconstruction in near-infrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

Achievement of high photoluminescence quantum efficiency and thermal stability is challenging for near-infrared (NIR)-emitting phosphors. Here, we designed a “kill two birds with one stone” strategy to simultaneously improve quantum efficiency and thermal stability of the NIR-emitting Ca3Y2-2x(ZnZr)xGe3O12:Cr garnet system by chemical unit cosubstitution, and revealed universal structure-property relationship and the luminescence optimization mechanism. The cosubstitution of [Zn2+–Zr4+] for [Y3+–Y3+] played a critical role as reductant to promote the valence transformation from Cr4+ to Cr3+, resulting from the reconstruction of octahedral sites for Cr3+. The introduction of [Zn2+–Zr4+] unit also contributed to a rigid crystal structure. These two aspects together realized the high internal quantum efficiency of 96% and excellent thermal stability of 89%@423 K. Moreover, information encryption with “burning after reading” was achieved based on different chemical resistance of the phosphors to acid. The developed NIR-emitting phosphor-converted light-emitting diode demonstrated promising applications in bio-tissue imaging and night vision. This work provides a new perspective for developing high-performance NIR-emitting phosphor materials.

Bulk crystal growth and characterization of intrinsic scintillator CaNb2O6

Single crystal CaNb2O6 was grown by the optical floating-zone method and characterized for a new intrinsic scintillator. Under Ar and O2 growth atmospheres, the as-grown crystal rods (Ф 4–5 mm) exhibit a greyish and a colorless appearance, respectively, which are related with the oxygen vacancy. They both show a broad emission band with the maximum at 480 nm under UV excitation, while the one grown in O2 is brighter with a photoluminescence quantum efficiency of 44%. Consequently, a 25% higher scintillation light yield was obtained in the crystals grown in O2 compared to those in Ar. The other scintillation properties including radioluminescence spectrum, pulsed X-ray decay and afterglow were also characterized and compared.

Phosphine-Oxide-Balanced Intra- and Interchain Through-Space Charge Transfer in Thermally Activated Delayed Fluorescence Polymers: Beyond 30% External Quantum Efficiency.

Through-space charge transfer (TSCT) is crucial for developing highly efficient thermally activated delayed fluorescence polymers. The balance of intra- and interchain TSCT can markedly improve performance, but it is still a big challenge. In this work, an effective strategy for "intra- and interchain TSCT balance" is demonstrated by way of a series of non-conjugated copolymers containing a 9,9-dimethylacridine donor and triazine-phosphine oxide (PO)-based acceptors. Steady-state and transient emission spectra indicate that compared to the corresponding blends, the copolymers can indeed achieve balanced intra- and interchain TSCT by accurately optimizing the inductive and steric effects of the acceptors. The DPOT acceptor with the strongest electron-withdrawing ability and the second bigger steric hindrance endows its copolymers with state-of-the-art photoluminescence and electroluminescence quantum efficiencies beyond 95% and 32%, respectively. This demonstrates that, compared to other congeners, the synergistic inductive and steric effects effectively enhance TSCT in DPOT-based copolymers for radiation, and suppress singlet and triplet quenching. The record-high efficiencies of its devices make this kind of copolymers hold the potential for low-cost, large-scale, and high-efficiency applications.

Bright circularly polarized photoluminescence in chiral layered hybrid lead-halide perovskites.

Hybrid perovskite semiconductor materials are predicted to lock chirality into place and encode asymmetry into their electronic states, while softness of their crystal lattice accommodates lattice strain to maintain high crystal quality with low defect densities, necessary for high luminescence yields. We report photoluminescence quantum efficiencies as high as 39% and degrees of circularly polarized photoluminescence of up to 52%, at room temperature, in the chiral layered hybrid lead-halide perovskites (R/S/Rac)-3BrMBA2PbI4 [3BrMBA = 1-(3-bromphenyl)-ethylamine]. Using transient chiroptical spectroscopy, we explain the excellent photoluminescence yields from suppression of nonradiative loss channels and high rates of radiative recombination. We further find that photoexcitations show polarization lifetimes that exceed the time scales of radiative decays, which rationalize the high degrees of polarized luminescence. Our findings pave the way toward high-performance solution-processed photonic systems for chiroptical applications and chiral-spintronic logic at room temperature.

8-Phenylquinoline-Based Tetradentate 6/6/6 Platinum(II) Complexes for Near-Infrared Emitters.

A series of novel tetradentate 6/6/6 Pt(II) complexes containing an 8-phenylquinoline-benzo[d]imidazole-carbazole ligand was designed; the Pt(II) complexes could be synthesized by metalizing the corresponding ligand with K2PtCl4 in high isolated yields of 60-90%. Experimental and theoretical studies suggested that the ligand modification of the quinoline moieties of the Pt(II) complexes could tune their electrochemical, photophysical, and excited-state properties. Notably, all the Pt(II) complexes exhibited highly electrochemical stabilities with reversible redox processes except the quasi-reversible reduction of PtYL3. The large π-conjugation of the ligand together with increased metal-to-ligand charge-transfer (3MLCT) characters in T1 states enabled the Pt(II) complexes to show broad Gaussian-type NIR emission spectra with high photoluminescence quantum efficiencies of 1.2-1.5% and short τ of 0.8-1.5 μs in dichloromethane at room temperature. This work should provide a valuable reference for the design and development of monomer NIR emitters.

Growth and Scintillation Properties of Na+-Doped CsCu2I3 Single Crystals

CsCu2I3 crystal is a promising Cu-based halide material for scintillation detection. In this paper, Na+ ion-doped CsCu2I3 crystals with a size of ϕ12 mm × 50 mm were grown successfully using the vertical Bridgman method, and the properties were systematically investigated. CsCu2I3:Na crystals exhibit yellow light emission peaking at 575 nm and a large Stokes shift of 1.55 eV. Based on the results of the XRD and XPS, the Na+ was introduced successfully. The optical absorption spectra show that the band gap of CsCu2I3 crystals was narrowed when the Na+ was doped. The photoluminescence quantum efficiency (PLQY) is improved from 16.4% to 19.6%. Finally, the X-ray-induced afterglow, and scintillation (energy resolution, light yield and decay time) under a 137Cs source were measured and discussed. These results illustrate that CsCu2I3:Na crystals have potential applications in the radiation detection field.

Enhanced Charge Balance for Efficient Electroluminescence from Cesium Copper Halides.

Cesium copper halides have the advantages of high photoluminescence quantum efficiency and good stability, making them attractive for replacing toxic lead halides in the field of perovskite light-emitting diodes (LEDs). However, due to their shallow conduction band and the lack of electron transport layers compatible with it, it remains a great challenge to achieve charge balance in LED devices. This drawback manifests as the accumulation of holes at the interface between the emitting layer and electron transport layer, resulting in nonradiative recombination. Here, we demonstrate an effective approach to address this issue by suppressing hole injection, which is realized through modification of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) layer with polyethylenimine. This leads to cesium-copper-halide LEDs with a high external quantum efficiency of 5.6%, representing an advance in device architecture for efficient electroluminescence from cesium copper halides.