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Hole-collecting monolayers have drawn attention in perovskite solar cell research due to their ease of processing, high performance, and good durability. Since molecules in the hole-collecting monolayer are typically composed of functionalized π-conjugated structures, hole extraction is expected to be more efficient when the π-cores are oriented face-on with respect to the adjacent surfaces. However, strategies for reliably controlling the molecular orientation in monolayers remain elusive. In this work, multiple phosphonic acid anchoring groups were used to control the molecular orientation of a series of triazatruxene derivatives chemisorbed on a transparent conducting oxide electrode surface. Using infrared reflection absorption spectroscopy and metastable atom electron spectroscopy, we found that multipodal derivatives align face-on to the electrode surface, while the monopodal counterpart adopts a more tilted configuration. The face-on orientation was found to facilitate hole extraction, leading to inverted perovskite solar cells with enhanced stability and high-power conversion efficiencies up to 23.0%.

Tin-based halide PVK films grown on organic CTLs have better crystallization than inorganic ones and photogenerated holes seem easier to be extracted than electrons from the film.

The lattice dynamics of CsSnX3(X = Cl, Br, and I) and CsPbI3, which are low-thermal-conductivity materials, are investigated using first-principles phonon calculations. Because of the strong lattice anharmonicity and the accompanying instability of high-temperature cubic phases, the self-consistent phonon theory, which can incorporate the effect of lattice anharmonicity at a mean-field level, is applied in this study. The calculated lattice thermal conductivity reproduced a low thermal conductivity, as shown experimentally, owing to the short phonon lifetime due to the incoherent scattering contribution of Cs atoms. The halogen ion dependence on thermal conductivity reveals that CsSnCl3exhibits an anomalous lattice thermal conductivity that is as low as that of CsSnBr3. This indicates that the lattice dynamics cannot be explained merely in terms of the atomic mass of the compounds. The low thermal conductivity of CsSnCl3is caused by the exceptionally short phonon lifetime; further, a bonding analysis suggests that covalent bonding contributes significantly to the unusual anharmonicity of CsSnCl3.

Research on tin–lead (SnPb) perovskite solar cells (PSCs) has gained popularity in recent years because of their low band gap, which could be applied to tandem solar cells. However, most of the work is based on inverted PSCs using PEDOT:PSS as the hole-transport layer as normal-structure PSCs show lower efficiency. In this work, the reason behind the low efficiency of normal-structure SnPb PSCs is elucidated and surface passivation has been tested as a method to overcome the problem. In the case of normal PSCs, at the interface between the titania layer and SnPb perovskite, there are many carrier traps observed originating from Ti–O–Sn bonds. In order to avoid the direct contact between titania and the SnPb perovskite layer, the titania surface is passivated with carboxylic acid C60resulting in an efficiency increase from 5.14 to 7.91%. This will provide a direction of enhancing the efficiency of the normal-structure SnPb PSCs through heterojunction engineering.

In the composition of Q0.1(FA0.75MA0.25)0.9SnI3, Q is replaced with Na+, K+, Cs+, ethylammonium+(EA+), and butylammonium+(BA+), respectively, and the relationship between actually measured lattice strain and photovoltaic performances is discussed. The lattice strain evaluated by the Williamson–hall plot of X-ray diffraction data decreased as the tolerance factor was close to one. The efficiency of the Sn-perovskite solar cell was enhanced as the lattice strain decreased. Among them, EA0.1(FA0.75MA0.25)0.9SnI3having lowest lattice strain gave the best result of 5.41%. Because the carrier mobility increased with a decrease in the lattice strain, these lattice strains would disturb carrier mobility and decrease the solar cell efficiency. Finally, the results that the efficiency of the SnGe-perovskite solar cells was gradually enhanced from 6.42 to 7.60% during storage, was explained by the lattice strain relaxation during the storage.

The efficiency of Sn-perovskite solar (Sn-PVK) cells was enhanced by adding 1% Samarium iodide (SmI2). Increase in Jscand FF is associated with the enhancement of efficiency and and explained by lower series resistance. SmI2is known as a strong reducing agent and is oxidized to Sm3+by reducing a substrate. By adding 1 and 5% SmI2, the carrier concentration of Sn-perovskite layer due to the presence of Sn4+was decreased from 4.8 × 1022/cm3to 1.2 × 1019/cm3and 6.1 × 1018/cm3respectively, because of the suppression of the oxidation from Sn2+to Sn4+by the strong reducing properties of SmI2. The low charge carrier concentration is also associated with the enhanced solar cell efficiency.The efficiency of Sn-perovskite solar (Sn-PVK) cells was enhanced by adding 1% of Samarium iodide (SmI2). Increase in Jscand FF is associated with the enhancement of the efficiency. They were explained by lower series resistance. SmI2is known as a strong reduced agent and is oxidized to Sm3+by reducing the substrate. By adding 1 and 5% of SmI2, the carrier concentration of Sn-perovskite layer due to the presence of Sn4+was decreased from 4.8 × 1022/cm3to 1.2 × 1019/cm3and 6.1 × 1018/cm3respectively, because of the suppression of the oxidation from Sn2+to Sn4+by the strong reducing properties of SmI2. The low charge carrier concentration is also associated with the enhanced solar cell efficiency.

The reaction selectivity of an electrode catalyst can be modulated by regulating its crystal structure, and the modified electrode may show different CO2reduction selectivity from that of its constituent metal. In this study, we investigated the mechanisms of the electrochemical CO2reduction on an electrodeposited Cu3Sn alloy by experimental and theoretical analyses. The electrodeposited Cu3Sn alloy electrode showed selectivity for CO production at all the applied potentials, and HCOOH production increased with an increase in the applied potential. In particular, hydrocarbon generation was well suppressed on Cu3Sn(002). To understand this selectivity change in electrochemical CO2reduction, we conducted density functional theory calculations for the reaction on the Cu3Sn(002) surface. According to the theoretical analysis, the Cu sites in Cu3Sn(002) contributed more to the stabilization of H*, COOH*, and CO* as compared with the Sn sites. Furthermore, the results indicated that Cu3Sn(002) decreased the surface coverage of reaction intermediates such as H*, COOH*, and CO*. We believe that these effects promoted CO* desorption while suppressing H2generation, CO* protonation, and C–C bond formation. The results also suggested that the surface Sn concentration significantly affected the reaction selectivity for HCOOH production from CO2.

We have performed elastic neutron scattering experiments on the superconductor La1.85Ho0.03Sr0.12CuO4to study the effect of substitution of a cation with a large magnetic moment at La site on the static spin correlation. In the Ho-free sample with a hole concentration of 0.12, the spatially-modulated magnetic order is known to be stabilized at temperature below Tspin∼30 K. In the present Ho-doped sample, we found the appearance of magnetic peaks at (0.5, 0.5 ± 0.119, 0) positions below Tspin∼35 K, which is similar to the observation in the pristine sample. Furthermore, the volume-corrected intensities in the Ho-free and Ho-doped samples are comparable, suggesting a negligible effect of Ho-substitution at La sites. These results are quite a contrast to the huge enhancement of the magnetic intensity and the increase of Tspinby substituting a comparable amounts of magnetic Fe3+ions onto CuO2planes. Therefore, the stability of the stripe order induced by the cation substitution is sensitive to the site at which the substitution occurs.

The crystal and magnetic structures of polycrystalline BiCoO3 have been determined by the Rietveld method from neutron diffraction data measured at temperatures from 5 to 520 K. BiCoO3 (space group P4mmZ = 1; a = 3.72937(7) Å and c = 4.72382(15) Å at room temperature; tetragonality c/a = 1.267) is isotypic with BaTiO3 and PbTiO3 in the whole temperature range. BiCoO3 is an insulator with a Néel temperature of 470 K. A possible model for antiferromagnetic order is proposed with a propagation vector of k = (1/2, 1/2, 0). In this model, magnetic moments of Co3+ ions are parallel to the c direction and align antiferromagnetically in the ab plane. The antiferromagnetic ab layers stack ferromagnetically along the c axis, forming a C-type antiferromagnetic structure. Refined magnetic moments at 5 and 300 K are 3.24(2)μB and 2.93(2)μB, respectively. The structure refinements revealed no deviation from stoichiometry in BiCoO3. BiCoO3 decomposed in air above 720 K to give Co3O4 and sillenite-like Bi25CoO39.

Transition-metal sulfide SnS2has aroused wide concern due to its high capacity and nanosheet structure, making it an attractive choice as the anode material in sodium-ion batteries. However, the large volume expansion and poor conductivity of SnS2lead to inferior cycle stability as well as rate performance. In this work, FeS2was in situ introduced to synchronously grow with SnS2on rGO to prepare a heterojunction bimetallic sulfide nanosheet SnS2/FeS2/rGO composite. The composition and distinctive structure facilitate the rapid diffusion of Na+and improve the charge transfer at the heterogeneous interface, providing sufficient space for volume expansion and improving anode materials’ structural stability. SnS2/FeS2/rGO bimetallic sulfide electrode boasts a capacity of 768.3 mA h g–1at the current density of 0.1 A g–1, and 541.2 mA h g–1at the current density of 1 A g–1in sodium-ion batteries, which is superior to that of either single metal sulfide SnS2or FeS2. TDOS calculation further confirms that the binding of FeS2/SnS2–Na is more stable than FeS2and SnS2alone. The superior electrochemical performance of the SnS2/FeS2/rGO composite material makes it a promising candidate for sodium storage.

Despite the similarities of the optoelectronic properties between tin halide and lead halide perovskites, the performance of tin perovskite solar cells (PSCs) is still far below that of lead PSCs with highest reported efficiency to date of around 10%. This is due to the chemical instability of tin halide perovskite crystals and the energy band levels mismatch between the perovskite and charge transport layers. In this work, tin halide PSCs with efficiency of more than 13% has been fabricated by regulating the A site cation to achieve a tolerance factor of nearly 1. The partial substitution of formamidinium cation with ethylammonium cation affords a more stable tin perovskite crystal and at the same time suppresses the trap density by as much as 1 order of magnitude. Furthermore, the more favourable energy levels of the EA-substituted tin perovskites enhanced the charge extraction process into the charge transport layers and thus reducing the charge carrier recombination. This work provides a proof that tin-halide PSCs has the potential to compete with more toxic lead-based PSCs, and hopefully will pave the future direction for fabricating more efficient and stable lead-free PSCs.

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