Although lambda 5-phosphinine derivatives are known as a promising class of blue fluorescent emitters, those photoluminescent quantum yield (PLQY) values have been reached up to 92 %, however, only a few examples have been explored as an emitter for blue organic light-emitting device (OLED), and the external quantum efficiency (EQE) has been below 2.4 % so far. In this study, we newly developed two types of blue lambda 5-phosphinine derivatives namely CN-COCF3 and CO2Me-CHO, and investigated the photophysical properties in the solid states. The photophysical analyses in solid state films suggested that the strong electron-accepting nature of these lambda 5-phosphinine derivatives caused the inferior PLQY values, and the exciplex formation with the host and neighboring materials should be avoided to improve the device efficiency. By choosing suitable host and neighboring materials with deep ionization potentials, we successfully realized efficient blue fluorescent OLEDs with EQE of over 4 % and CIE (0.14, 0.18). This is among the best in lambda 5-phosphinine-based blue OLEDs so far.

In this study on perovskite solar cells (PVSCs), we incorporate N-benzylhydroxylamine (N-BzHoA) as an additive into the precursor solution. The addition of N-BzHoA suppressed the formation of unwanted PbI _2 and δ-phase perovskite without affecting the band gap, confirming uniform and large grains in the perovskite film. The fabricated inverted PVSCs exhibited remarkably improved properties compared to the control device, with a power conversion efficiency of 17.49%, reduced hysteresis, and more than 89% retention of the initial capacity after 100 h of light exposure. Thus, this study highlights the effectiveness of N-BzHoA as an effective additive for inverted PVSCs.

Although Earth-abundant, ubiquitous, metal-based thermally activated delayed fluorescence (TADF) complexes are among the most promising candidate materials for next-generation organic light-emitting devices (OLEDs), few complexes are explored. Herein, a highly emissive aluminum(III)-TADF complex-Al(MCzDBM)(3)-with three beta-diketone ligands is presented as a sensitizer for multiresonance (MR)-TADF emitters. This complex exhibited green emission with suitable photophysical functions as a sensitizer, such as a high photoluminescent quantum yield (PLQY) of up to 97% with reduced aggregation-caused quenching, a high radiative rate constant (k(r)) of 5.6 x 10(7) s(-1), and a short delayed lifetime (tau(d)) of 4.0 mu s in the solid state. A solution-processed Al(MCzDBM)(3)-based OLED exhibited an external quantum efficiency (EQE) of 23.6%. This complex sensitized a yellow MR-TADF emitter, yielding a near-unity PLQY, and is used to fabricate a solution-processed hyperfluorescent OLED with an EQE of 21.6% and full width at half maximum of 45 nm.

Blue phosphors are indispensable in constructing organic light-emitting diodes (OLEDs). Herein, we reported two Ir(III) complexes, namely f-CN1 and f-CN2, with asymmetrically arranged benzo[d]imidazolylidenes, to which the peri-cyano substituent has concurrently induced both the selective aryl cyclometalation and emission tuning in giving one single blue Ir(III) phosphor. With the aforementioned 'one stone for two birds' tactics, these carbene complexes exhibited photoluminescent peak (lambda(max)) at similar to 472 nm and excellent quantum yields (83-100 %) in doped thin films. Consequently, the fabricated OLED devices delivered maximum external quantum efficiencies (EQE(max)) of 23.6 % and 20.2 %, respectively. Furthermore, hyper-OLED devices with f-CN1 and multi-resonant TADF terminal emitter m-DiNBO displayed an EQE(max) of 30.8 % with CIEx,y coordinates of (0.13, 0.10), together with impressive EQE of 26.9 % at practical brightness of 100 cd m(-2).

The transition dipole moments of a heteroleptic iridium complex are actively controlled by using cyano-containing carbazole-based hosts. The orientation ratio ( Θ ) is improved from 65% to 78%. The Θ value is correlated with the T g value of host material.

The horizontal orientation of the emissive transition dipole moment (TDM) of emissive molecules is a crucial factor in improving the efficiency of organic light-emitting diodes (OLEDs). However, the mechanism of this horizontal orientation remains unclear. Herein, to elucidate the horizontal orientation mechanism of the TDM of the molecules in thermally activated delayed fluorescent (TADF) emitters, the relationship between the horizontal orientation ratio (Theta) of the TDM and the key parameters of stick-like TADF emitters dispersed in carbazole-based host materials is systematically and quantitatively investigated. The introduction of functional groups containing weak CH/n (n = O, N) hydrogen bonds into the host material is found to significantly increase the Theta values up to 30%. The physical parameters of the dispersed emitter exhibit a strong relationship with the Theta values, with the following influence order: glass transition temperature (Tg) >= total surface area of the largest pi-plane and the corresponding parallel pi-plane > molecular weight > aspect ratio > permanent dipole moment. The Tg value of the host material is another key parameter determining the Theta values. By using a P=O-based host material, namely mCP2PO, a high PLQY of 97%, a high Theta value of 88%, and a sky-blue OLED with an EQE of 37.6% are simultaneously realized.

Three phenylene-bridged MR-TADF emitters with different numbers of carbazole units are developed. These emitters exhibit sky-blue emission around 480 nm with a small FWHM of ∼31 nm, near-unity PLQY, and an EQE of nearly 30%.

A series of β-diketone-based TADF emitters named MCzX derivatives are designed and prepared. Among these emitters, MCzDBM exhibits a PLQY of 79%, horizontal emission dipole orientation ratio of 88%, and high EQE of approximately 25%.

A highly luminescent mononuclear Al complex with beta-diketone ligands exhibiting superior thermally activated de-layed fluorescence (TADF) properties was developed in this work. The complex showed yellow emission with promising photofunctions, including a near-unity photoluminescence quantum yield (PLQY), a rapid radiative decay rate, and a short delayed fluorescence lifetime in the solid state. When applied in a solution-processed organic light-emitting device, an external quantum efficiency (EQE) exceeding 18% and a low turn-on voltage of 2.9 V at 1 cd/m2 were obtained, sur-passing those of the corresponding beta-diketone ligand. Metal complexation with Al generated unique electronic structures that significantly strengthened the photofunctions of the origi-nal beta-diketone ligand in the solid state.

All inorganic cesium lead halide perovskite with CsPbX 3 (X = Cl - , Br - , or I - ) have been demonstrated a novel classified colloidal quantum dots (QDs). Perovskite QDs have also expected great potential for the application in light-emitting devices (LEDs) due to their superior chemical stability, narrow emission spectra enable coverage the next generation of standard for display, B.T. 2020 color gamut, high photoluminescence quantum yields (PLQYs) of up to 90%, plainly tunable emission wavelength in full visible range by halide anion composition (X site = Cl - for blue emission, Br - for green emission, or I - for red emission) or size of QDs. Perovskite QDs are consisted almost entirely of inorganic elements, the energy levels of perovskite QDs are similar to the organic light-emitting materials, which lead to fabrication of device with similar structure of organic light-emitting devices (OLEDs). The external quantum efficiency (EQE) of LEDs based on CsPbX 3 QDs have rapidly increased from 0.1% to over 20% for past only few years.

Here, we demonstrate anion-exchange red perovskite QDs CsPb(Br/I)3 from pristine CsPbBr3 using ammonium-iodine salts, long alkyl-based oleylammonium iodide (OAM-I) and aryl-based aniline hydoroiodide (An-HI), for use in highly efficient light-emitting devices (LEDs). The anion-exchange CsPb(Br/I)3 films exhibit a strong red-shift in their of photoluminescence (PL) spectrum from the green emission at 508 nm in the case of the pristine QDs to one in the deep-red region at 649 nm owing to the replacement of Br– anions by I–¬ anions in the perovskite QDs. LEDs formed using the anion-exchange CsPb(Br/I)3 based on OAM-I show an remarkable high EQE of more than 20% as well as high color purity, with the Commission Internationale de l'Eclairage (CIE) at (0.72, 0.28), which completely cover BT.2020 color gamut. Similarly, the LEDs formed using the QDs based on An-HI show a peak EQE of 14.1% and CIE coordinates of (0.71, 0.28). Further, they exhibit longer operational stability as compared to that of LEDs formed using the OAM-I-based CsPb(Br/I)3.

Perovskite quantum dots have significant potential for light-emitting devices because of their high colour purity and colour tunability in the visible spectrum. Here, we report highly efficient red perovskite quantum dot-based light-emitting devices. The quantum dots were fabricated by anion exchange from pristine CsPbBr3 using halide-anion-containing alkyl ammonium and aryl ammonium salts. Anion-exchange quantum dots based on ammonium iodine salts exhibited a strong redshift from green emission to a deep-red emission at 649 nm as well as higher photoluminescence quantum yields. Furthermore, the quantum dot-based light-emitting device with the alkyl ammonium iodine salt exhibited an external quantum efficiency of 21.3% and high colour purity, with Commission Internationale de l'Eclairage coordinates of (0.72, 0.28), while the light-emitting device with the aryl ammonium iodine salt showed an external quantum efficiency of 14.1%. Finally, the operational stability of the latter was 36 times higher because the surface ligand density of the corresponding quantum dots was lower.

Cesium lead halide (CsPbX3, X = Cl, Br, or I) perovskite quantum dots (QDs) are known as ionic nanocrystals, and their optical properties are greatly affected by the washing solvent used during the purification process. Here, we demonstrate the purification process of CsPbBr3 perovskite QDs using low-dielectric-constant solvents to completely remove impurities, such as the reaction solvent and desorbed ligands. The use of the ether solvent diethylene glycol dimethyl ether (diglyme), having a low dielectric constant of ε = 7.23, as a poor solvent for reprecipitation allowed for multiple wash cycles, which led to high purity and high photoluminescence quantum yield for CsPbBr3 QDs. The light-emitting device constructed with the CsPbBr3 QDs and washed twice with diglyme (two-wash) showed a low turn-on voltage of 2.7 V and a peak external quantum efficiency of over 8%. Thus, the purification of perovskite QDs with multiple wash cycles using a low-dielectric-constant solvent is an effective approach for enhancing not only the optical properties but also the efficiency of perovskite quantum dot light-emitting devices.

All inorganic perovskites quantum dots (PeQDs) have attracted much attention for used in thin film display applications and solid-state lighting applications, owing to their narrow band emission with high photoluminescence quantum yields (PLQYs), color tunability, and solution processability. Here, we fabricated low-driving-voltage and high-efficiency CsPbBr3 PeQDs light-emitting devices (PeQD-LEDs) using a PeQDs washing process with an ester solvent containing butyl acetate (AcOBu) to remove excess ligands from the PeQDs. The CsPbBr3 PeQDs film washed with AcOBu exhibited a PLQY of 42%, and a narrow PL emission with a full width at half-maximum of 19 nm. We also demonstrated energy level alignment of the PeQD-LED in order to achieve effective hole injection into PeQDs from the adjacent hole injection layer. The PeQD-LED with AcOBu-washed PeQDs exhibited a maximum power efficiency of 31.7 lm W-1 and EQE of 8.73%. Control of the interfacial PeQDs through ligand removal and energy level alignment in the device structure are promising methods for obtaining high PLQYs in film state and high device efficiency.