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A cyclometalated Pt(IV) compound, Pt[(dfpypy).sub.2](Me)Cl (1), with blue phosphorescence was prepared using 2',6'-dinuoro-2,3'-bipyridine (dfpypy) as a C^N chelate ligand. Compound 1 exhibits distorted octahedral geometries around the platinum ion and has strong intermolecular interactions via interatomic contacts (H***N/F/Cl) involving hydrogen bond interactions based on Hirshfeld surface analysis. This compound shows bright blue phosphorescence emissions with [[lambda].sub.max] = 427 and 455 nm and a high photoluminescence quantum efficiency ([[PHI].sub.PL] = 0.60). Furthermore, a good blue colour purity with Commission Internationale de L'Eclairage (1931) coordinates (x, y) of (0.14, 0.17) was observed in the thin film, which was close to pure blue. TD-DFT calculations revealed that the electronic transition can be attributed to a combination of intraligand charge transfer ([[pi].sub.bpy] - [[pi]*.sub.bpy]) and ligand-to-ligand charge transfer [[p.sub.z](Cl)-[pi]*(dfpypy)] with a small contribution from metal-to-ligand charge transfer ([Pt.sub.d]-[[pi]*.sub.bpy]). Owing to the introduction of the electronegative C[and]N chelate dfpypy, the emission of compound 1 was blueshifted by 20 nm compared with its analog [[Pt(ppy).sub.2](Me)Cl] ([[lambda].sub.max] = 447), where ppy is 2-phenylpyridine. Key words: blue phosphorescence, quantum efficiency, colour purity, intraligand charge transfer, ligand-to-ligand charge transfer Nous avons préparé un composé cyclométallé à base de Pt(IV), le Pt(dfpypy)2(Me)Cl (1), présentant une phosphorescence bleue dans lequel la 2',6'-difluoro-2,3'-bipyridine (dfpypy) est utilisée comme ligand chélatant C[and]N. Selon l'analyse de surface d'Hirshfeld, le composé 1 présente une géométrie octaédrique déformée autour de l'ion platine et de fortes interactions intermoléculaires par contacts interatomiques (H***N/F/Cl) impliquant des liaisons hydrogène. Ce composé produit des émissions phosphorescentes bleu vif aux longueurs d'onde [[lambda].sub.max] de 427 et de 455 nm et présente une efficacité quantique de photo luminescence élevée (rendement quantique de photoluminescence, [[PHI].sub.PL] = 0,60). En outre, la couleur bleue observée dans le film mince était d'une bonne pureté selon les coordonnées de la Commission internationale de l'éclairage (1931) [x = 0,14, y = 0,17], qui correspondent à une couleur proche du bleu pur. D'après des calculs basés sur la théorie de la fonctionnelle de la densité dépendante du temps (TD-DFT), la transition électronique serait attribuable majoritairement au transfert de charge intraligand (TCIL, [[pi].sub.bpy]-[[pi]*.sub.bpy]) et au transfert de charge de ligand à ligand [TCLL, [p.sub.z](Cl)-[pi]*(dfpypy)], et dans une moindre mesure au transfert de charge du métal au ligand (TCML, [Pt.sub.d]-[[pi]*.sub.bPy]). L'ajout du chelate C[and]N électronégatif dfpypy a eu pour effet de décaler de 20 nm vers le bleu l'émission du composé 1 par rapport à son analogue [Pt[(ppy).sub.2](Me)Cl] ([[lambda].sub.max] = 447; ppy = 2-phénylpyridine). [Traduit par la Rédaction] Mots-clés : phosphorescence bleue, efficacité quantique, pureté de couleur, transfert de charge intraligand, transfert de charge de ligand à ligand, 1. Introduction Recently, bipyridine (pypy = 2,3'-bipyridine) ligand-based cyclometalated iridium(III) and platinum(II) compounds have attracted considerable interest owing to their excellent external quantum efficiency (EQE) in blue phosphorescent organic light-emitting [...]

Abstract Perovskite solar cells (PSCs) expressed great potentials for offering a feasible alternative to conventional photovoltaic technologies. 2D/3D hybrid PSCs, where a 2D capping layer is used over the 3D film to avoid the instability issues associated with perovskite film, have been reported with improved stabilities and high power conversion efficiencies (PCE). However, the profound analysis of the PSCs with prolonged operational lifetime still needs to be described further. Heading towards efficient and long-life PSCs, in-depth insight into the complicated degradation processes and charge dynamics occurring at PSCs' interfaces is vital. In particular, the Au/HTM/perovskite interface got a substantial consideration due to the quest for better charge transfer; and this interface is debatably the trickiest to explain and analyze. In this study, multiple characterization techniques were put together to understand thoroughly the processes that occur at the Au/HTM/perovskite interface. Inquest analysis using current–voltage (I–V), electric field induced second harmonic generation (EFISHG), and impedance spectroscopy (IS) was performed. These techniques showed that the degradation at the Au/HTM/perovskite interface significantly contribute to the increase of charge accumulation and change in impedance value of the PSCs, hence resulting in efficiency fading. The 3D and 2D/3D hybrid cells, with PCEs of 18.87% and 20.21%, respectively, were used in this study, and the analysis was performed over the aging time of 5000 h. Our findings propose that the Au/HTM/perovskite interface engineering is exclusively essential for attaining a reliable performance of the PSCs and provides a new perspective towards the stability enhancement for the perovskite-based future emerging photovoltaic technology.

The current study provides an insight into the thermal stability of perovskite solar cells (PSCs) and the factors causing their degradation. To this end, a systematic stability study was carried out on n-i-p type perovskite solar cells involving mesoporous TiO2 layer. The samples were subjected to varying moisture and thermal conditions under light soaking while being exposed to long-term indoor (5000 h) and outdoor (75 h) harsh environmental conditions (i.e. 30%-80% RH and 40 °C-70 °C). To identify performance and morphological changes of PSCs after exposure to thermal stress, advanced characterization techniques including impedance spectroscopy, scanning electron microscopy and glow discharge optical emission spectrometry along with I-V characteristics were used. The un-encapsulated samples exposed to high thermal stress (40-70 °C) show degradation in their efficiency more than 40% within the 75 h of thermal stress. In contrast, the samples that were kept at room temperature were found to be very stable over 5000 h. [ABSTRACT FROM AUTHOR]

In the title compound, [Ag(CF 3 SO 3 )(C 10 H 6 F 2 N 2 ) 2 ], the Ag I centre adopts a highly distorted trigonal-planar coordination environment resulting from its coordination by one O atom of the tri-fluoro-methane-sulfonate anion and the pyridine N atoms of two crystallographically independent 2',6'-di-fluoro-2,3'-bi-pyridine ligands, which display very similar conformations to one another. Pairwise Ag⋯O-SO 2 CF 3 - [Ag⋯O = 2.8314 (14) Å] inter-actions and inter-molecular C-H⋯O inter-actions between inversion-related units lead to the formation of an eight-membered cyclic dimer in which the silver atoms are separated by 6.2152 (3) Å. In the crystal, the dimers are linked through C-H⋯O hydrogen bonds, halogen⋯π and weak π-π stacking inter-actions, resulting in the formation of a three-dimensional supra-molecular network. The title compound exhibits a strong and broad emission band from 400 nm to 550 nm in solution and its photoluminescence quantum efficiency is estimated to be ca 0.2, indicating that the title compound could have applications as an emitting material in organic light-emitting diodes (OLEDs)., (© Moon et al. 2021.)

The title compound, [Pt(C 21 H 12 F 2 N 3 O)Cl], crystallizes with two crystallographically independent mol-ecules ( A and B ) in the asymmetric unit, which adopt similar conformations. The Pt II atoms in both mol-ecules adopt distorted square-planar geometries, coordinated by one C and two N atoms from the tridentate 2',6'-di-fluoro-6-[3-(pyridin-2-yl-oxy)phen-yl]-2,3'-bi-pyridine ligand and a chloride anion: the C and Cl atoms are trans . In the crystal, C-H⋯Cl/F hydrogen bonds, F⋯π and weak π-π stacking inter-actions between adjacent A and B mol-ecules and between pairs of inversion-related B mol-ecules lead to the formation of a two-dimensional supra-molecular network lying parallel to the ab plane. The sheets are stacked along the c- axis direction and linked by F⋯π and weak π-π stacking inter-actions between pairs of inversion-related A mol-ecules, forming a three-dimensional supra-molecular network. The photoluminescence quantum efficiency of the title compound in the blue-green region of the visible region (λ max = 517 and 544 nm) is estimated to be ∼0.2-0.3, indicating that the title compound could be a suitable candidate as the emitting material in organic light-emitting diode (OLED) applications., (© Park et al. 2021.)