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Significant interest exists in water-tolerant 2D lead iodide perovskites owing to their stability and proven potential in photovoltaic and photonic applications. These materials have solid-state phase transitions that are accessible below 100 °C. Here, the study witnesses the multiple phase transitions of the last members of a series of organic–inorganic hybrid materials, [(CnH2n+1NH3)2PbI4], with even n as n = 14, 16, and 18, once again. By employing temperature-dependent steady-state photoluminescence (PL) and temperature-dependent time-resolved photoluminescence (TRPL) spectroscopy in the temperature range of −18 to +90 °C and at −196 °C, we explore the thermal responses of these materials. The investigation reveals reversible phase transitions occurring between room temperature (RT) and elevated temperatures, impacting the optical properties and emitting colors of the perovskite compounds. The longer the alkyl chain, the higher the phase transition temperature, attributed to increased conformational disorder and enhanced perovskite symmetry. The decay constants for all compounds are very close in value, which confirms the underlying excited-state dynamics, pointing to contributions primarily from inorganic components across different phases. We anticipate that our results on the detection of phase transitions in 2D perovskites will not only motivate the use of these techniques for detecting phase transitions but also would help to understand their excited states in more details to selectively use them for solar cell and next-generation display technologies. [ABSTRACT FROM AUTHOR]

Electrochemical impedance spectroscopy (EIS) is a commonly used steady-state technique to examine the internal resistance of electron-transfer processes in solar cell devices, and the results are directly related to the photovoltaic performance. In this study, EIS was performed to study the effects of accelerated ageing, aiming for insights into the degradation mechanisms of dye-sensitized solar cells (DSSCs) containing cobalt tris(bipyridine) complexes as redox mediators. Control experiments based on aged electrolytes differing in concentrations of the redox couple components and cation co-additives were conducted to reveal the correlation of the cell degradation with external and internal properties. The failure modes of the cells emerged as changes in the kinetics of charge- and ion-transfer processes. An insufficient concentration of the redox complexes, in particular Co(III), was found to be the main reason for the inferior performance after ageing. The related characterization of electrolytes aged outside the solar cell devices confirms the loss of active Co(III) complexes in the device electrolytes. A new EIS feature at low frequencies emerged during ageing and was analysed. The new EIS feature demonstrates the presence of an unexpected rate-limiting, charge-transfer process in aged devices, which can be attributed to the TiO2/electrolyte interface. High-resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) was performed to identify the reduction of a part of Co(III) to Co(II) after ageing, by investigating the Co K absorption edge. The HERFD-XAS data suggested a partial reduction of Co(III) to Co(II), accompanied by a difference in symmetry of the reduced species. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have emerged as attractive materials for use in solar cells, light emitting diodes and other optoelectronic devices, mainly due to their impressive charge transport properties, strong light absorption, long carrier diffusion lengths and long excited state lifetime. The extensive research on these materials has paved the way for a new class of materials: metal halide perovskite nanocrystals (NCs). Due to their high photoluminescence quantum yield and narrow emission that can be tuned by size and compositional variations, perovskite NCs are considered to be ideal candidates compared to traditional quantum dots. With the growing interest in these materials and the current challenges in their commercialization, this review aims mainly to provide the necessary understanding of the influence of capping ligands on the synthesis and application of perovskite NCs. The different synthetic approaches and the role of ligands in determining the morphological and optical properties of the resulting NCs will be discussed. Thereafter, we review the advances in understanding the surface chemistry and ligation in the metal halide perovskite NCs. Lastly, we review the ligand exchange and management processes that are shown to be beneficial in improving the performance and stability of perovskite nanocrystal films for optoelectronic applications. [ABSTRACT FROM AUTHOR]

An ultrasound-assisted extraction (leaching) method of valuable metals from discarded lithium-ion batteries (LiBs) is reported. Mild organic citric or acetic acids were used as leaching agents for a more environmentally-friendly recovery of the lithium, nickel, cobalt, and manganese from the discharged and crushed lithium nickel-manganese-cobalt oxide (NMC) LiBs. The extraction was performed with the presence/absence of continuous ultrasound (US) energy supplied by a 110 W ultrasonic bath. The effect of temperature (30–70 °C), reducing agent concentration (H2O2: 0–2.0 vol%), as well as choice of specific acid on the metal dissolution were investigated. The US leaching decreased the leaching time by more than 50% and improved the leached percentage of Li, Mn, Co, and Ni due to the local heat and improved mass transfer between solid and liquid interfaces in the process. The X-ray diffraction results of residues from the US leaching further confirmed an improved dissolution of the crushed layered NMC structure, resulting in the significant improvement of the leached amounts of the valuable metals. Furthermore, it is demonstrated that using citric acid eliminated the need of additional reducing agents and suppressed the dissolution of copper (Cu) due to its inhibitor effect on the Cu surface, i.e. compared with using acetic acid as leaching reagent. Overall, it is shown that recovery of the battery metals can be facilitated and carried out in a more energy-efficient manner at low temperatures (50 °C) using ultrasound to improve metal ions mass transportation in the residue layers of the NMC during the organic acid leaching. [ABSTRACT FROM AUTHOR]

Single crystals of Spiro(TFSI)2 were grown, the optical and electronic properties were characterized and compared with neutral Spiro-OMeTAD. Density-functional theory was used to get insights into binding and band structure properties. The flat valence bands indicate a rather limited orbital overlap in Spiro(TFSI)2. [ABSTRACT FROM AUTHOR]

We report the significant role of synthetic routes and the importance of solvents in the synthesis of organic–inorganic lead iodide materials. Through one route, the intercalation of dimethylformamide in the crystal structure was observed leading to a one--dimensional (1D) [NH3(CH2)4NH3]Pb2I6 structure of the product. This product was compared with the two-dimensional (2D) [NH3(CH2)4NH3]PbI4 recovered from aqueous solvent based synthesis with the same precursors. UV-visible absorption spectroscopy showed a red-shift of 0.1 eV for the band gap of the 1D network in relation to the 2D system. This shift primarily originates from a shift in the valence band edge as determined from photoelectron- and X-ray spectroscopy results. These findings also suggest the iodide 5p orbital as the principal component in the density of states in the valence band edge. Single crystal data show a change in the local coordination around iodide, while in both materials, lead atoms are surrounded by iodide atoms in octahedral units. The conductivity of the one-dimensional material ([NH3(CH2)4NH3]Pb2I6) was 50% of the two-dimensional material ([NH3(CH2)4NH3]PbI4). The fabricated solar cells reflect these changes in the chemical and electronic structure of both materials, although the total light conversion efficiencies of solar cells based on both products were similar. [ABSTRACT FROM AUTHOR]

The synthetic route and properties of three 2D hybrid organic/inorganic lead iodide perovskite materials are reported. The 2D perovskites were synthesized from the reaction between PbI2 and the di-cations of 1,4-diaminobutane, 1,6-diaminohexane, and 1,8-diaminooctane. The resulting products were [NH3(CH2)4NH3]PbI4 (BdAPbI4), [NH3(CH2)6NH3]PbI4 (HdAPbI4), and [NH3(CH2)8NH3]PbI4 (OdAPbI4). Structural characterization shows that two dimensional perovskite structures were formed with inorganic structural planes separated by organic layers. Absorption spectra show band gaps of 2.37 eV (BdAPbI4), 2.44 eV (HdAPbI4), and 2.55 eV (OdAPbI4). The 2D perovskite materials were investigated as light absorbing materials in solid state solar cells. The best performing material under moist, ambient conditions was BdAPbI4 (1.08% efficiency), which was comparable to methylammonium Pb(ii) iodide (MAPbI3) solar cells (2.1% efficiency) manufactured and studied under analogous conditions. When compared to MAPbI3, the 2D materials have larger band gaps and lower photoconductivity, while BdAPbI4 based solar cells shows a comparable absorbed photon-to-current efficiency as compared to MAPbI3 based ones. [ABSTRACT FROM AUTHOR]

Alkylammonium lead(ii) iodide materials (APbI3), based on the general formula of CH3–(CH2)n–NH3PbI3, may lead to a monumental leap in developing affordable photovoltaics. Herein, we correlate the structure and function relationships of alkylammonium lead(ii) iodide in solar cells. We investigated changes in the structure of APbI3 materials by varying the alkylammonium cations in their structure. As the size of the alkylammonium cation increased, the crystallographic unit cell increased in size and yielded lower symmetry crystals. High symmetry materials, those with cubic symmetry, showed the highest conductivity, the smallest bandgap, and produced the best performing solar cells. Structural changes were investigated by X-ray crystallography, X-ray powder diffraction, and Raman scattering. [ABSTRACT FROM AUTHOR]

Recently, cobalt redox electrolyte mediators have emerged as a promising alternative to the commonly used iodide/triiodide redox shuttle in dye-sensitized solar cells (DSCs). Here, we report the successful use of a new quasi-liquid, polymer-based electrolyte containing the Co3+/Co2+ redox mediator in 3-methoxy propionitrile solvent in order to overcome the limitations of high cell resistance, low diffusion coefficient and rapid recombination losses. The performance of the solar cells containing the polymer based electrolytes increased by a factor of 1.2 with respect to an analogous electrolyte without the polymer. The performances of the fabricated DSCs have been investigated in detail by photovoltaic, transient electron measurements, EIS, Raman and UV-vis spectroscopy. This approach offers an effective way to make high-performance and long-lasting DSCs. [ABSTRACT FROM AUTHOR]

The oxidation of iodide to diiodide, I2−, by the metal-to-ligand charge-transfer (MLCT) excited state of [Ru(deeb)3]2+, where deeb is 4,4′-(CO2CH2CH3)2-2,2′-bipyridine, was quantified in acetonitrile and dichloromethane solution at room temperature. The redox and excited state properties of [Ru(deeb)3]2+were similar in the two solvents; however, the mechanisms for excited state quenching by iodide were found to differ significantly. In acetonitrile, reaction of [Ru(deeb)3]2+*and iodide was dynamic (lifetime quenching) with kinetics that followed the Stern–Volmer model (KD= 1.0 ± 0.01 × 105M−1, kq= 4.8 × 1010M−1s−1). Excited state reactivity was observed to be the result of reductive quenching that yielded the reduced ruthenium compound, [Ru(deeb−)(deeb)2]+, and the iodine atom, I. In dichloromethane, excited state quenching was primarily static (photoluminescence amplitude quenching) and [Ru(deeb−)(deeb)2]+formed within 10 ns, consistent with the formation of ion pairs in the ground state that react rapidly upon visible light absorption. In both solvents the appearance of I2−could be time resolved. In acetonitrile, the rate constant for I2−growth, 2.2 ± 0.2 × 1010M−1s−1, was found to be about a factor of two slower than the formation of [Ru(deeb−)(deeb)2]+, indicating it was a secondary photoproduct. The delayed appearance of I2−was attributed to the reaction of iodine atoms with iodide. In dichloromethane, the growth of I2−, 1.3 ± 0.4 × 1010M−1s−1, was similar to that in acetonitrile, yet resulted from iodine atoms formed within the laser pulse. These results are discussed within the context of solar energy conversion by dye-sensitized solar cells and storage viachemical bond formation. [ABSTRACT FROM AUTHOR]

Inverse-vulcanized polymeric sulfur has been prepared and utilized for solid-state dye sensitized solar cells. A power conversion efficiency of 1.5% was recorded with a short-circuit current of 4.1 mA cm−2 and an open-circuit voltage of 0.75 V under standard AM 1.5G illumination (1000 W m−2). The results in the present study qualify the new polymeric sulfur material as a future candidate as low-cost, hole-transport material for solid-state dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]

Correction for ‘Structure and function relationships in alkylammonium lead(ii) iodide solar cells’ by Majid Safdari et al., J. Mater. Chem. A, 2015, DOI: 10.1039/c4ta06174h. [ABSTRACT FROM AUTHOR]

We report on the synthesis and characterization of a donor-acceptor ruthenium polypyridyl complex as a photosensitizer for p-type dye-sensitized solar cells (DSSCs). The electrochemical, photophysical, and photovoltaic performance of two ruthenium-based photosensitizers were tested in NiO-based DSSCs; bis-(2,2'-bipyridine-4,4'-dicarboxylic acid)(2)N-(1,10-phenanthroline)-4-nitronaphthalene-1,8-dicarboximide ruthenium(II), ([Ru(dcb)(2)(NMI-phen)](PF(6))(2)) and tris-(2,2'-bipyridine-4,4'-dicarboxylic acid)(3) ruthenium(ii), [(Ru(dcb)(3))Cl(2)]. The presence of an electron-accepting group, 4-nitronaphthalene-1,8-dicarboximide (NMI), attached to the phenanthroline of [Ru(dcb)(2)(NMI-phen)](2+) resulted in long-lived charge separation between reduced [Ru(dcb)(2)(NMI-phen)](2+) and NiO valence band holes; 10-50 μs. In the reduced state for [Ru(dcb)(2)(NMI-phen)](2+), the electron localized on the distal NMI group. In tests with I(3)(-)/I(-) and Co(4,4'-di-tert-butyl-bipyridine)(3)(2+/3+) electrolytes, [Ru(dcb)(2)(NMI-phen)](2+) outperformed [Ru(dcb)(3)](2+) in solar cell efficiency in devices. A record APCE (25%) was achieved for a ruthenium photosensitizer in a p-type DSSC. Insights on photosensitizer regeneration kinetics are included.