Ligand Engineering Enables Efficient Pure Red Tin-Based Perovskite Light-Emitting Diodes

With increasing ecological and environmental concerns, tin (Sn)-based perovskite light-emitting diodes (PeLEDs) are competitive candidates for future displays because of their environmental friendliness, excellent photoelectric properties, and low-cost solution-processed fabrication. Nonetheless, their electroluminescence (EL) performance still lags behind that of lead (Pb)-based PeLEDs due to the fast crystallization rate of Sn-based perovskite films and undesired oxidation from Sn²⁺ to Sn⁴⁺, leading to poor film morphology and coverage, as well as high density defects. Here, we propose a ligand engineering strategy to construct high-quality phenethylammonium tin iodide (PEA₂SnI₄) perovskite films by using L-glutathione reduced (GSH) as surface ligands toward efficient pure red PEA₂SnI₄-based PeLEDs. We show that the hydrogen-bond and coordinate interactions between GSH and PEA₂SnI₄ effectively reduce the crystallization rate of the perovskites and suppress the oxidation of Sn²⁺ and formation of defects. The improved pure red perovskite films not only show excellent uniformity, density, and coverage but also exhibit enhanced optical properties and stability. Finally, state-of-the-art pure red PeLEDs achieve a record external quantum efficiency of 9.32 % in the field of PEA₂SnI₄-based devices. This work demonstrates that ligand engineering represents a feasible route to enhance the EL performance of Sn-based PeLEDs.     

Sn3N4, ein Zinn(IV)-nitrid – Synthese und erste Strukturbestimmung einer binären Zinn–Stickstoff-Verbindung

Sn₃N₄, a Tin(IV) Nitride – Syntheses and the First Crystal Structure Determination of a Binary Tin-Nitrogen Compound By reaction of SnI₄ with KNH₂ in liquid ammonia at 243 K a white product mixture was obtained. After evaporation of ammonia the solid residue was annealed in vacuum for 2–5 d at 573 K. Subsequently collected x-ray powder diffraction patterns exhibited reflections of KI and a new compound Sn₃N₄. Analogous reactions of SnBr₂ and KNH₂ led to KBr and dark brown microcrystalline Sn₃N₄ but also to metallic tin. The structure of tin(IV)-nitride was determined from X-ray and neutron powder diffraction data: Space group Fd 3 m, Z = 8, a = 9.037(3) Å. Sn₃N₄ crystallizes in a spinel type structure. Both metal atom positions are occupied by tin atoms of oxidation state plus four.     

SnI4⋅(S8)2: A Novel Adduct‐Type Infrared Second‐Order Nonlinear Optical Crystal

A simple adduct from tin tetraiodide SnI₄ and octasulfur S₈, SnI₄?(S₈)₂ ( 1 ), is obtained employing a facile reaction. The combination of Sn⁴⁺ ions with d¹⁰ electron configuration, acentric SnI₄ tetrahedra, and lone‐pair effects of S₈, makes 1 a phase‐matchable infrared NLO crystal with a moderate second‐harmonic generation (SHG) response and a very high laser‐induced damage threshold (LIDT), which is well confirmed by the DFT calculations.     

REACTIVITY OF HALIDE COMPLEXES OF TIN(II) I. The Reduction of Methyl Orange

Abstract

Halide ion is required for the reduction of methyl orange by Sn(II). Equilibrium data on the formation of SnCl^2-n _n and SnI^2-n _n combined with kinetic data indicate that SnCl₃ ^? and SnI₃ ^? form activated complexes with protonated methyl orange. The data also suggest pathways involving SnCl₄ ^? SnCl₅ ³, SnI₅ ³ and SnI₇ ^5-.     

Stabilization of the unhybridized Sn2+ stannous ion in the BaClF structure and its characterization by119Sn Mössbauer spectroscopy

In divalent tin halides, when the halogen is small and highly electronegative (F, Cl), the tin valence orbitals are hybridized, the tin(II) non-bonded electron pair is located on one of the hybrid orbitals, and the resulting large electric field gradient gives a large quadrupole splitting. The reaction of barium chloride and tin difluoride in aqueous solutions, for large BaCl₂.2H₂O/SnF₂ ratios (>10) results in the precipitation of a white powdered material, which is identified by X-ray diffraction to be BaCIF. However, Tin-119 Mossbauer spectroscopy shows the material contains a fairly large amount of divalent tin in the Sn²⁺ ionic form, with unhybridized orbitals, like in SnCl₂. Using X-ray diffraction, we have established that Sn²⁺ ions substitute 15% of the Ba²⁺ ions at random, and chemical analysis shows the material has the formula Ba_5.66SnCl_7.30F_6.04 and thus is enriched in chlorine.     

A Cation‐Exchange Approach for the Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells

Tin‐based halide perovskite materials have been successfully employed in lead‐free perovskite solar cells, but the overall power conversion efficiencies (PCEs) have been limited by the high carrier concentration from the facile oxidation of Sn²⁺ to Sn⁴⁺. Now a chemical route is developed for fabrication of high‐quality methylammonium tin iodide perovskite (MASnI₃) films: hydrazinium tin iodide (HASnI₃) perovskite film is first solution‐deposited using presursors hydrazinium iodide (HAI) and tin iodide (SnI₂), and then transformed into MASnI₃ via a cation displacement approach. With the two‐step process, a dense and uniform MASnI₃ film is obtained with large grain sizes and high crystallization. Detrimental oxidation is suppressed by the hydrazine released from the film during the transformation. With the MASnI₃ as light harvester, mesoporous perovskite solar cells were prepared, and a maximum power conversion efficiency (PCE) of 7.13 % is delivered with good reproducibility.     

Exciton Localization for Highly Luminescent Two-Dimensional Tin-Based Hybrid Perovskites through Tin Vacancy Tuning

Exciton localization is an approach for preparing highly luminescent semiconductors. However, realizing strongly localized excitonic recombination in low-dimensional materials such as two-dimensional (2D) perovskites remains challenging. Herein, we first propose a simple and efficient Sn²⁺ vacancy (V_Sn) tuning strategy to enhance excitonic localization in 2D (OA)₂SnI₄ (OA=octylammonium) perovskite nanosheets (PNSs), increasing their photoluminescence quantum yield (PLQY) to ≈64 %, which is among the highest values reported for tin iodide perovskites. Combining experimental with first-principles calculation results, we confirm that the significantly increased PLQY of (OA)₂SnI₄ PNSs is primarily due to self-trapped excitons with highly localized energy states induced by V_Sn. Moreover, this universal strategy can be applied for improving other 2D Sn-based perovskites, thereby paving a new way to fabricate diverse 2D lead-free perovskites with desirable PL properties.     

Temperature-Dependent Photoluminescence of Hexafluorobenzene-Intercalated Phenethylammonium Tin Iodide 2D Perovskite

Tin halide perovskites are potential alternatives of lead halide perovskites. However, the easy oxidation of Sn²⁺ to Sn⁴⁺ brings in a challenge. Recently, layered two-dimensional hybrid tin halide perovskites have been shown to partially resist the oxidation process because of the presence of hydrophobic organic molecules. Consequently, such layered hybrid perovskites are being explored for optoelectronic applications. The optical properties of layered tin halide perovskites depend on the interlayer separation and the dielectric mismatch between the organic and inorganic layers. Intercalation (insertion) of a molecular species between the layers modifies the interlayer interactions affecting the optical properties of layered hybrid perovskites. We investigated the effect of hexafluorobenzene (HFB) intercalation in phenethylammonium tin iodide [(PEA)₂SnI₄] using temperature-dependent (6 K to 300 K) photoluminescence (PL). HFB intercalation increases the bandgap. A strong PL quenching is observed in pristine (PEA)₂SnI₄ below 150 K, probably because of the presence of non-emissive states. HFB intercalation suppresses the influence of such non-emissive states resulting in an increase in PL intensity at the cryogenic temperatures. Our results highlight that a simple molecular intercalation (non-covalent interaction) into layered hybrid perovskites can significantly tailor the electronic and optical properties.     

Antioxidant Grain Passivation for Air‐Stable Tin‐Based Perovskite Solar Cells

Tin‐based perovskites with excellent optoelectronic properties and suitable band gaps are promising candidates for the preparation of efficient lead‐free perovskite solar cells (PSCs). However, it is challenging to prepare highly stable and efficient tin‐based PSCs because Sn²⁺ in perovskites can be easily oxidized to Sn⁴⁺ upon air exposure. Here we report the fabrication of air‐stable FASnI₃ solar cells by introducing hydroxybenzene sulfonic acid or its salt as an antioxidant additive into the perovskite precursor solution along with excess SnCl₂. The interaction between the sulfonate group and the Sn²⁺ ion enables the in situ encapsulation of the perovskite grains with a SnCl₂–additive complex layer, which results in greatly enhanced oxidation stability of the perovskite film. The corresponding PSCs are able to maintain 80 % of the efficiency over 500 h upon air exposure without encapsulation, which is over ten times longer than the best result reported previously. Our results suggest a possible strategy for the future design of efficient and stable tin‐based PSCs.     

Cyclische Diazastannylene. XXVIII. Anorganische Polycyclen aus der Reaktion eines Bis(amino)-stannylens bzw. eines Iminostannylens mit SnCl2, SnBr2 und tert-Butoxizinn(II)-chlorid bzw. -bromid

Cyclic Diazastannylenes. XXVIII. Inorganic Polycyclic Compounds from the Reaction of Bis(amino)stannylene or Iminostannylene with SnCl₂, SnBr₂, and tert-Butoxitin(II) Chloride or Bromide The cyclic bis(amino)stannylene 1 may react with tert-butoxitin(II) chloride or bromide yielding a Lewis acid-base adduct 4 resp. 5 , in which the two molecules are held together via N→Sn (233.8(3) pm) and O→Sn (215.1(2) pm) bonds. The resulting adduct 4 contains therefore two four membered rings sharing one common edge as found by X-ray structure determination. If 1 is allowed to react with SnCl₂ or SnBr₂, the salts Me₂Si(N^tBu)₂Sn₂Br⁺Sn₂Br₅^? ( 7 ) are formed. Structure analysis reveals the cations in 6 and 7 to be very similar: SnCl⁺ and SnBr⁺ are coordinated by the “trihapto ligand” 1 in a way resulting a polycyclic SiN₂Sn₂X-arrangement. To a central Sn₂N₂ tetrahedron Si and halogen X are added occupying and bridging two opposite edges (mean values: N? Sn = 232(5) ( 6 ), N? Sn = 230(2) ( 7 ), Sn? C1 = 265(1), Sn? Br = 275(1) pm). The reaction intermediate (SnN^tBu)₂ adds to SnCl₂ to form the crystalline polymer ( ^tBuN)₂Sn₃C1₂ (8) . X-ray structure determination reveals the solid to be built up by one-dimensional chains of polycyclic Sn₃(N^tBu)₂C1₃ sharing two chlorine atoms with neighbouring units. The unit Sn₃(N^tBu)₂C1₃ can be visualized as an equilateral triangle of chlorine atoms, on which a smaller triangle of tin atoms is superimposed; the corners of the smaller triangle being located in the middle of the larger triangle's edges. The tin atoms are bipyramidally coordinated by two N? ^tBu-groups thus forming a nearly perfect Sn₃N_2s trigonal bipyramide (Sn? N = 222.7(3) pm). Two chlorine atoms of the triangle are connected to neighbouring units, the chlorine atoms thus attain an unusual nearly square-planar coordination sphere (Sn? Cl(mean) = 308(5) pm). The tertbutyl groups at the nitrogen atoms “screen” the inorganic part of the structure leading to a layer structure.     

Transition metal schiff base chelates as ligands for phenyltin(IV) chlorides

Summary Binuclear complexes of phenyltin(IV) chlorides with transition metal chelates of tetradentate Schiff bases derived from acetylacetone, benzoylacetone oro-hydroxyacetophenone and ethylenediamine or propylenediamine, of the general formula Ph_nSnCl₄-nML (where n = 1 or 2, M = Ni¹¹ or Cu¹¹ and L^2–= the Schiff base dianion), have been synthesised and characterized through elemental analysis, conductance and i.r. spectroscopic data. The coordination of metal chelates to tin involves two triply bonded oxygen atoms giving rise to an octahedral environment around Sn^IV. The molar conductance of the complexes in nitrobenzene shows the presence of the uncoordinated ML and phenyltin(IV) chloride moieties in solution.Author to whom all correspondence should be directed.     

The relationship between SnII fraction and visible light activated photocatalytic activity of SnOx·SiO2 glass studied by Mössbauer spectroscopy

The relationship between local structure and visible-light photocatalytic ability of tin silicate glass prepared by sol–gel method was investigated. ¹¹⁹Sn Mössbauer spectrum of SnO_x·SiO₂ glass prepared from SnCl₂ showed a small peak of Sn^II component besides the major amount of Sn^IV. The smallest bandgap energy of 2.5 ± 0.5 eV was estimated from Tauc plot, and the largest first order rate constant (k) of (13.8 ± 0.1) 10⁻³ min⁻¹ was recorded from the methylene blue degradation test under visible-light irradiation. It is concluded that Sn^II shows remarkable photocatalytic ability when it is incorporated into silica glass matrix.

     

The Reaction of SnCl2 with Br2 and I2 in Weak Donor Solvents

The compounds SnCl₂Br₂(MeCN)₂, “Sn₃Cl₈Br₄(THF)₆”, and “Sn₃Cl₁₀Br₂(OEt₂)₆” were obtained by reaction between SnCl₂ and Br₂ in acetonitrile (MeCN), tetrahydrofuran (THF) and diethyl ether (OEt₂). The two last are solid solutions of SnCl₄L₂ and SnCl₂Br₂L₂ (L = THF, OEt₂) in the proportions 1:2 and 2:1, respectively. The compounds are characterized by IR, Raman, and Mössbauer spectroscopy, a C₁ symmetry being found for SnCl₂Br₂ (MeCN)₂ together with a C_2v symmetry, with the ligands in trans positions, for SnCl₂Br₂L₂ (L = THF, OEt₂). The Mössbauer spectrum of SnBr₄(THF)₂ was also obtained, which has not previously been reported. The reaction between SnCl₂ and I₂ has also been studied in the same solvents, and the formation of SnCl₄L₂ (L = MeCN, THF, OEt₂), SnI₄, and a small amount of SnI₃Cl was observed, which have been identified by Raman spectroscopy.     

Ionische Kronenetherkomplexe von Zinn(II) und Zinn(IV): [Sn(15-Krone-5)] [SnCl6] und [SnCl3(18-Krone-6)]2[Sn2Cl10]; Synthesen,IR-Spektren und 119Sn-Mößbauer-Spektren

Ionic Crown Ether Complexes of Tin(II) and Tin(IV): [Sn(15-Crown-5)][SnCl₆] and [SnCl₃(18-Crown-6)]₂[Sn₂Cl₁₀]; Syntheses, IR Spectra, and ¹¹⁹Sn-Mössbauer Spectra [Sn(15-crown-5)][SnCl₆] ( 1 ,) has been prepared by the reaction of SnCl₂, SnCl₄, and 15-crown-5 in the molar ratio of 1 : 1 : 1 in acetonitrile solution, forming a white insoluble crystal powder. [SnCl₃(18-crown-6)]₂[Sn₂Cl₁₀] ( 2 ,) as well as [SnCl₃(18-crown-6)][BiCl₄] · CH₃CN ( 3 ,) are prepared by the reaction of SnCl₄ with 18-crown-6 (molar ratio 2 : 1), and of SnCl₄, 18-crown-6, and BiCl₃ (molar ratio 1 : 1 : 1), respectively. According to IR-spectroscopy and ¹¹⁹Sn-Mössbauer-spectroscopy 1–3 , have ionic structures; the cation of 1 , being polymeric via a sandwich-like structure.     

Schwache Sn…I‐Wechselwirkungen in den Kristallstrukturen der Iodostannate [SnI4]2– und [SnI3]–

Weak Sn…I Interactions in the Crystal Structures of the Iodostannates [SnI₄]^2– and [SnI₃]^– Iodostannate complexes can be crystallized from SnI₂ solutions in polar organic solvents by precipitation with large counterions. Thereby isolated anions as well as one, two or three‐dimensional polymeric anionic substructures are established, in which SnI₃^– and SnI₄^2– groups are linked by weak Sn…I interactions. Examples are the iodostannates [Me₃N–(CH₂)₂–NMe₃][SnI₄] ( 1 ), (Ph₄P)₂[Sn₂I₆] ( 2 ), [Me₃N–(CH₂)₂–NMe₃][Sn₂I₆] ( 3 ), [Fe(dmf)₆][SnI₃]₂ ( 4 ) and (Pr₄N)[SnI₃] ( 5 ), which have been characterized by single crystal X‐ray diffraction. [Me₃N–(CH₂)₂–NMe₃][SnI₄] ( 1 ): a = 671.6(2), b = 1373.3(4), c = 2046.6(9) pm, V = 1887.7(11) · 10⁶ pm³, space group Pbcm;(Ph₄P)₂[Sn₂I₆] ( 2 ): a = 1168.05(6), b = 717.06(4), c = 3093.40(10) pm, β = 101.202(4)°, V = 2541.6(2) · 10⁶ pm³, space group P2₁/n;[Me₃N–(CH₂)₂–NMe₃][Sn₂I₆] ( 3 ): a = 695.58(4), b = 1748.30(8), c = 987.12(5) pm, β = 92.789(6)°, V = 1199.00(11) · 10⁶ pm³, space group P2₁/c;[Fe(dmf)₆][SnI₃]₂ ( 4 ): a = 884.99(8), b = 1019.04(8), c = 1218.20(8) pm, α = 92.715(7), β = 105.826(7), γ = 98.241(7), V = 1041.7(1) · 10⁶ pm³, space group P1;(Pr₄N)[SnI₃] ( 5 ): a = 912.6(2), b = 1205.1(2), c = 1885.4(3) pm, V = 2073.5(7) · 10⁶ pm³, space group P2₁2₁2₁.     

Distannabarrelenes with Three Coordinated SnII Atoms

Crystalline 1,4-distannabarrelene compounds [(ADC^Ar)₃Sn₂]SnCl₃ ( 3 - Ar ) (ADC^Ar={ArC(NDipp)₂CC}; Dipp=2,6-iPr₂C₆H₃, Ar=Ph or DMP; DMP=4-Me₂NC₆H₄) derived from anionic dicarbenes Li(ADC^Ar) ( 2 - Ar ) (Ar=Ph or DMP) have been reported. The cationic moiety of 3 - Ar features a barrelene framework with three coordinated Sn^II atoms at the 1,4-positions, whereas the anionic unit SnCl₃ is formally derived from SnCl₂ and chloride ion. The all carbon substituted bis-stannylenes 3 - Ar have been characterized by NMR spectroscopy and X-ray diffraction. DFT calculations reveal that the HOMO of 3 - Ph (ϵ=−6.40 eV) is mainly the lone-pair orbital at the Sn^II atoms of the barrelene unit. 3 - Ar readily react with sulfur and selenium to afford the mixed-valence Sn^II/Sn^IV compounds [(ADC^Ar)₃SnSn(E)](SnCl₆)_0.5 (E=S 4 - Ar , Ar=Ph or DMP; E=Se 5 - Ph ).     

Polarography of tin(II) chloride in acetonitrile

Polarographic and spectrophotometric data show that tin(II) chloride is a weak electrolyte in dilute acetonitrile solutions. The dominant species, SnCl₂, exists in a labile equilibrium with the ions SnCl⁺ and SnCl₃^- Oxidation and reduction of these ionic species is responsible for all observed polarographic plateaux. The dichloro—tin(II) molecule is shown to be a good acceptor species in acetonitrile solution, readily forming 1:1 complexes with ligands such as 4-picoline N-oxide.     

The liquid—liquid extraction of platinum in the presence of tin(II) chloride from dilute hydrochloric acid into 4-methyl-2-pentanone

The distribution of complexes of type [Pt(SnCl₃)_nCl_4?n]^2? (n = 1–4) and [Pt(SnCl₃)₅]^3? between 1.5–3.5 M hydrochloric acid and 4-methyl-2-pentanone is discussed in detail. Platinum can be quantitatively extracted into the organic phase from hydrochloric acid solutions containing tin(II) chloride when the mole ratio Sn²⁺: Pt²⁺ > 5. In the presence of sufficient tin(II) chloride, the [Pt(SnCl₃)₅]^3? anion is the predominant species extracted into the organic phase. Similar results pertain to starting solutions of either Ptcl^2?₄ or PtCl^2?₆, although Pt⁴⁺ is rapidly reduced to Pt²⁺. Small amounts of Co²⁺, Ni²⁺, Fe³⁺ and Cu²⁺ do not interfere.     

[{Cp*(CO)2Fe}6Sn6O8]2+, ein kationischer Zinnoxocluster mit metallorganischen Substituenten

[{Cp*(CO)₂Fe}₆Sn₆O₈]²⁺, a Cationic Tin Oxo Cluster with Organometallic Substituents The reaction of [{Cp*(CO)₂Fe}SnCl₃] 1 (Cp^* = Pentamethylcyclopentadienyl) with Ag₂O in acetone leads to the formation of [{Cp*(CO)₂Fe}₆Sn₆O₈][AgCl₂]₂( 2 ). 2 contains the novel tin oxo cluster cation [{Cp*(CO)₂Fe}₆Sn₆O₈]²⁺ which consists of six {Cp*(CO)₂Fe}Sn‐groups bridged by eight μ₃ oxygen atoms (Sn—O = 209.2(3)‐212.5(3) pm). The resulting Sn₆O₈ cage exhibits a distorted rhombodocahedral structure. The [AgCl₂]^— anion is essentially linear with a Ag—Cl bond length of 250.3(3) pm.     

Bis‐aroylhydrazone based on 2,2′‐bis substituted diphenylamine for synthesis of new binuclear organotin (IV) complexes: Spectroscopic characterization,crystal structures,in vitro DNA‐binding,plasmid DNA cleavage,PCR and cytotoxicity against MCF7 cell line

New dinuclear organotin (IV) complexes, Me₄Sn₂L, Ph₄Sn₂L and Bu₄Sn₂L, have been synthesized from reaction of R₂SnCl₂ (R = Me, Ph and Bu) with a 2,2′‐bis‐substituted diphenylamine arοylidene hydrazone, H₄L. The synthesized compounds were investigated by elemental analysis and infrared, ¹H‐NMR and ¹¹⁹Sn‐NMR spectroscopy. The structures of H₄L, Me₄Sn₂L and Bu₄Sn₂L were also confirmed by X‐ray crystallography. H₄L molecules adopt (E)‐configuration and keto‐tautomeric form in the solid state. In all complexes, the bis‐hydrazone acts as a tetra‐anionic ligand with two contiguous ONO tridentate domains that coordinate the two R₂Sn moieties in the enolate form. The coordination environments of both tin centers are five‐coordinate. DNA‐binding studies were performed by UV–Vis spectroscopy, and the results indicate that the synthesized compounds significantly interact with calf thymus‐DNA in the intercalative mode. The results of polymerase chain reaction assay show that all the compounds affect on amplification of DNA, and complexes are more effective than ligands. The in vitro cytotoxicity against the human breast cancer line (MCF7) was determined using the MTT assay, and H₄L and the dibutytin complex showed higher activity.