Engineering Stable Lead-Free Tin Halide Perovskite Solar Cells: Lessons from Materials Chemistry.

Substituting toxic lead with tin (Sn) in perovskite solar cells (PSCs) is the most promising route toward the development of high-efficiency lead-free devices. Despite the encouraging efficiencies of Sn-PSCs, they are still yet to surpass 15% and suffer detrimental oxidation of Sn(II) to Sn(IV). Since their first application in 2014, investigations into the properties of Sn-PSCs have contributed to a growing understanding of the mechanisms, both detrimental and complementary to their stability. This review summarizes the evolution of Sn-PSCs, including early developments to the latest state-of-the-art approaches benefitting the stability of devices. The degradation pathways associated with Sn-PSCs are first outlined, followed by describing how composition engineering (A, B site modifications), additive engineering (oxidation prevention), and interface engineering (passivation strategies) can be employed as different avenues to improve the stability of devices. The knowledge about these properties is also not limited to PSCs and also applicable to other types of devices now employing Sn-based perovskite absorber layers. A detailed analysis of the properties and materials chemistry reveals a clear set of design rules for the development of stable Sn-PSCs. Applying the design strategies highlighted in this review will be essential to further improve both the efficiency and stability of Sn-PSCs.

High Power Irradiance Dependence of Charge Species Dynamics in Hybrid Perovskites and Kinetic Evidence for Transient Vibrational Stark Effect in Formamidinium.

Hybrid halide perovskites materials have the potential for both photovoltaic and light-emitting devices. Relatively little has been reported on the kinetics of charge relaxation upon intense excitation. In order to evaluate the illumination power density dependence on the charge recombination mechanism, we have applied a femtosecond transient mid-IR absorption spectroscopy with strong excitation to directly measure the charge kinetics via electron absorption. The irradiance-dependent relaxation processes of the excited, photo-generated charge pairs were quantified in polycrystalline MAPbI3, MAPbBr3, and (FAPbI3)0.97(MAPbBr3)0.03 thin films that contain either methylamonium (MA) or formamidinium (FA). This report identifies the laser-generated charge species and provides the kinetics of Auger, bimolecular and excitonic decay components. The inter-band electron-hole (bimolecular) recombination was found to dominate over Auger recombination at very high pump irradiances, up to the damage threshold. The kinetic analysis further provides direct evidence for the carrier field origin of the vibrational Stark effect in a formamidinium containing perovskite material. The results suggest that radiative excitonic and bimolecular recombination in MAPbI3 at high excitation densities could support light-emitting applications.

Solid Solution Metal Chalcogenides for Sodium-Ion Batteries: The Recent Advances as Anodes.

The sodium-ion battery (SIB) has attracted ever growing attention as a promising alternative of the lithium-ion battery (LIB). Constructing appropriate anode materials is critical for speeding up the application of SIB. This review aims at guiding anode design from the material's perspective, and specifically focusing on solid solution metal chalcogenide anode. The sodium ion storage mechanisms of a solid solution metal chalcogenide anode is overviewed on basis of the elements it is composed of, and discusses how the solid solution character alters the electrochemical performances through diffusion and surface-controlled processes. In addition, by classifying solid solution metal chalcogenide as cation and anion, their recent applications are updated, and understanding the roles of guest elements in improving the electrochemical behaviors of a solid solution metal chalcogenide is carried out. After that, discussion of possible strategies to further optimize these anode materials in the future, flowing from crystal structure design to morphology control and finally to the intimacy improvement between conductive matrix and solid solution metal chalcogenide are also provided.

Degradation mechanism of hybrid tin-based perovskite solar cells and the critical role of tin (IV) iodide.

Tin perovskites have emerged as promising alternatives to toxic lead perovskites in next-generation photovoltaics, but their poor environmental stability remains an obstacle towards more competitive performances. Therefore, a full understanding of their decomposition processes is needed to address these stability issues. Herein, we elucidate the degradation mechanism of 2D/3D tin perovskite films based on (PEA)0.2(FA)0.8SnI3 (where PEA is phenylethylammonium and FA is formamidinium). We show that SnI4, a product of the oxygen-induced degradation of tin perovskite, quickly evolves into iodine via the combined action of moisture and oxygen. We identify iodine as a highly aggressive species that can further oxidise the perovskite to more SnI4, establishing a cyclic degradation mechanism. Perovskite stability is then observed to strongly depend on the hole transport layer chosen as the substrate, which is exploited to tackle film degradation. These key insights will enable the future design and optimisation of stable tin-based perovskite optoelectronics.

Ultrathin polymethylmethacrylate interlayers boost performance of hybrid tin halide perovskite solar cells.

Introducing a polymethylmethacrylate (PMMA) layer at the (PEA)0.2(FA)0.8SnI3 perovskite/hole transport layer interface leads to a remarkable improvement in the photogenerated current density and fill factor, resulting in an increase in the power conversion efficiency from 6.5% to 10%. PMMA is proposed to mitigate interfacial charge losses and to induce a more favourable distribution of 2D perovskite phases, elucidating a pathway towards the development of high-performance tin-based perovskite solar cells.

2D Phase Purity Determines Charge-Transfer Yield at 3D/2D Lead Halide Perovskite Heterojunctions.

Targeted functionalization of 3D perovskite with a 2D passivation layer via R-NH3I treatment has emerged as an effective strategy for enhancing both the efficiency and chemical stability of ABX3 perovskite solar cells, but the underlying mechanisms behind these improvements remain unclear. Here, we assign a passivation mechanism where R-NH3I reacts with excess PbI2 in the MAPbI3 film and unsaturated PbI6 octahedra to form (R-NH3)2(MA)n-1PbnI3n+1. Crucially, we show that precise control of the 2D (R-NH3)2(MA)n-1PbnI3n+1 layer underpins performance improvements: n = 1 yields over a 2-fold improvement in hole injection to the HTL; n > 1 deteriorates hole injection. Ultrafast transient absorption spectroscopy suggests this n-dependence is rooted in the fact that fast (<6 ns) hole injection does not occur between the 3D and 2D layers. These results help explain contemporary empirical findings in the field and set out an important design rule for the further optimization of multidimensional perovskite optoelectronics.

Fine mapping of a palea defective 1 (pd1), a locus associated with palea and stamen development in rice.

KEY MESSAGE : pd1, a genetic factor in a 69 kb region between RM11239 and RM11245 on rice chromosome 1, controls stamen number and palea development. Spikelets are important organs that store photosynthetic products in rice. Spikelet development directly affects grain yield and rice quality. Here, we report a palea defective (pd1) mutant identified from selfing progenies of indica cv. 93-11 after (60)Co γ ray treatment. pd1 mutant flowers only had four stamens (wild-type has six), but pollen fertility was not affected. Compared with 93-11 palea, pd1 mutant palea showed smaller and flatter leaf, which caused the lemma to bend excessively inward. pd1 mutants had only 46% seed setting rate and 21.6 g 1000-grain weight, which led to two-thirds loss of grain yield. Scanning electron microscope analysis revealed that pd1 mutants had reduced epidermal cell size and reduced numbers of fibrous sclerenchyma cells in both palea and lemma. To analyze the genetic factors involved, we crossed pd1 mutants with three japonica cultivars and generated F1 and F2 populations. The F1 phenotype and F2 segregation ratio indicated that a recessive gene controlled the mutant traits. Using the F2 population, we found that pd1 mapped between the simple sequence repeat markers RM11236 and RM11280 on rice chromosome 1. From a segregating population of 2836 plants, 77 recombinants were screened by RM11236 and RM11280. High-resolution linkage analysis narrowed the pd1 locus to a 69 kb region between RM11239 and RM11245 that contained 10 open reading frames (ORFs). Sequence alignment and quantitative real-time PCR expression analysis of these ORFs between 93-11 and pd1 mutant plants found no unequivocal evidence to identify the pd1 gene.