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1. Tuning cesium–guanidinium in formamidinium tin triiodide perovskites with an ethylenediammonium additive for efficient and stable lead-free perovskite solar cells

   https://doi.org/10.1039/d0ma00520g  

   Tosado, Gabriella A.; Zheng, Erjin; Yu, Qiuming (December 2020, Materials Advances)

   null (Ed.)

   Achieving efficient and stable tin-based perovskite solar cells remains challenging. In this work, we incorporate the ethylenediammonium diiodide (EDAI 2 ) additive into a cesium–guanidinium doped formamidinium tin triiodide perovskite with the composition of (CsGA) x FA 1−2x SnI 3 + y % EDAI 2 . This new perovskite utilizes the strong hydrogen bonding of the guanidinium cation and the lattice strain relaxation of the small cesium cation as well as the hollowing and passivation effects of the EDAI 2 additive. The EDAI 2 additive not only yields pinhole-free cubic phase perovskite films but also decreases both shallow and deep trap states in the perovskite films. These effects are pronounced with the increase of substitution of the pair of GA + and Cs + . The new perovskites are deployed in inverted planar solar cells. A maximum power conversion efficiency (PCE) of 5.01% is achieved with the (CsGA) 0.15 FA 0.70 SnI 3 + 0% EDAI 2 device but the device degrades after storage in a nitrogen-filled glove box for 30 days. Both performance and stability are improved with the addition of EDAI 2 . A maximum PCE of 5.72% is achieved with the (CsGA) 0.15 FA 0.70 SnI 3 + 1.0% EDAI 2 device. The (CsGA) 0.15 FA 0.70 SnI 3 + 1.5% EDAI 2 devices exhibit a maximum PCE of 5.69% and the performance is further increased to 6.39% after storage in a nitrogen-filled glove box for 4 days; 70% of the initial PCE is retained after 45 days. This study demonstrates the benefit of tuning cation sizes and introducing divalent cations to integrate stabilizing factors into pure Sn perovskites, creating new routes for efficient and stable lead-free perovskite solar cells. 

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2. Room temperature synthesis of lead-free FASnI ₃ perovskite nanocrystals with improved stability by SnF ₂ additive

   https://doi.org/10.1063/5.0125100  

   Chen, Zeying; Dhakal, Tara P. (March 2023, Applied Physics Reviews)

   Tin halide perovskites are among the candidates for replacing lead-based ones for less toxicity and comparable optical properties. However, stability remains a challenge due to the easier oxidation of Sn 2+ than Pb 2+ . Here, for the first time, we applied the ligand-assisted reprecipitation method to synthesize CH(NH 2 ) 2 SnI 3 (FASnI 3 ) orthorhombic perovskite nanocrystals with an average diameter of 7.7 nm and a photoluminescence emission at 825 [Formula: see text] 2 nm (1.5 eV). The influence of synthesis parameters, including precursor solvent, precipitation media, temperature, and time on optical properties of nanocrystals, was studied. By incorporating SnF 2 , the stability of the nanocrystals was improved, and the oxidation from FASnI 3 to FA 2 SnI 6 was significantly delayed, which was quantitively demonstrated and confirmed by observing the characteristic diffraction peaks of the perovskite phase using x-ray diffraction at various exposure time to air. The addition of SnF 2 is optimized to be 6%. The FASnI 3 nanocrystals stayed stable for at least 265 days under N 2 storage at room temperature and relative humidity of 20%. 

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3. Kinetic versus thermodynamic metalation enables synthesis of isostructural homo- and heterometallic trinuclear clusters

   https://doi.org/10.1039/d0cc02346a  

   Hyun, Sung-Min; Upadhyay, Apoorva; Das, Anuvab; Burns, Corey P.; Sung, Siyoung; Beaty, Jeremy D.; Bhuvanesh, Nattamai; Nippe, Michael; Powers, David C. (June 2020, Chemical Communications)

   null (Ed.)

   Temperature-dependent metalation of the new hexadentate ligand (tris(5-(pyridin-2-yl)-1 H -pyrrol-2-yl)methane; H 3 TPM) enables the selective synthesis of both mononuclear ( i.e. Na(THF) 4 [Fe(TPM)], kinetic product) and trinuclear ( i.e. Fe 3 (TPM) 2 , thermodynamic product) complexes. Exposure of Na(THF) 4 [Fe(TPM)] to FeCl 2 or ZnCl 2 triggers cluster expansion to generate homo- or heterometallic trinuclear complexes, respectively. The developed approach enables systematic variation of ion content in isostructural metal clusters via programmed assembly. 

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4. Kinetically Controlled Growth of Sub‐Millimeter 2D Cs ₂ SnI ₆ Nanosheets at the Liquid–Liquid Interface

   https://doi.org/10.1002/smll.202006279  

   Zhu, Weiguang; Shen, Junhua; Li, Mingxin; Yang, Kun; Bu, Wei; Sun, Yi‐Yang; Shi, Jian; Lian, Jie (December 2020, Small)

   Abstract Cs₂SnI₆perovskite displays excellent air stability and a high absorption coefficient, promising for photovoltaic and optoelectronic applications. However, Cs₂SnI₆‐based device performance is still low as a result of lacking optimized synthesis approaches to obtain high quality Cs₂SnI₆crystals. Here, a new simple method to synthesize single crystalline Cs₂SnI₆perovskite at a liquid–liquid interface is reported. By controlling solvent conditions and Cs₂SnI₆supersaturation at the liquid–liquid interface, Cs₂SnI₆crystals can be obtained from 3D to 2D growth with controlled geometries such as octahedron, pyramid, hexagon, and triangular nanosheets. The formation mechanisms and kinetics of complex shapes/geometries of high quality Cs₂SnI₆crystals are investigated. Freestanding single crystalline 2D nanosheets can be fabricated as thin as 25 nm, and the lateral size can be controlled up to sub‐millimeter regime. Electronic property of the high quality Cs₂SnI₆2D nanosheets is also characterized, featuring a n‐type conduction with a high carrier mobility of 35 cm²V⁻¹s⁻¹. The interfacial reaction‐controlled synthesis of high‐quality crystals and mechanistic understanding of the crystal growth allow to realize rational design of materials, and the manipulation of crystal growth can be beneficial to achieve desired properties for potential functional applications. 

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5. ipso -Arylative polymerization as a route to π-conjugated polymers: synthesis of poly(3-hexylthiophene)

   https://doi.org/10.1039/C8PY00605A  

   Shih, Feng-Yang; Tian, Sisi; Gallagher, Nicholas; Park, Young S.; Grubbs, Robert B. (January 2018, Polymer Chemistry)

   ipso -Arylative cross-coupling with two 3-hexylthiophene derivatives, (5-bromo-4-hexylthiophen-2-yl)diphenylmethanol and 2-(5-bromo-4-hexylthiophen-2-yl)propan-2-ol, has been used to prepare poly(3-hexylhiophene) (P3HT) as a model conjugated polymer. P3HT with number-average molecular weights ranging from 8–20 kg mol −1 ( Đ 1.4–2.2) was prepared from 5-bromo-4-hexylthiophen-2-yl)diphenylmethanol with a Pd(OAc) 2 /PCy 3 /Cs 2 CO 3 catalyst system. Only oligomerization of 2-(5-bromo-4-hexylthiophen-2-yl)propan-2-ol ( M n ≈ 3 kg mol −1 ) was observed under similar conditions. Studies with model compounds suggest that side reactions involving end-group loss limit ultimate molecular weights. 

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