Impact of the Solvation State of Lead Iodide on Its Two‐Step Conversion to MAPbI3: An In Situ Investigation

Producing high efficiency solar cells without high‐temperature processing or use of additives still remains a challenge with the two‐step process. Here, the solution processing of MAPbI₃ from PbI₂ films in N,N‐dimethylformamide (DMF) is investigated. In‐situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) measurements reveal a sol–gel process involving three PbI₂‐DMF solvate complexes—disordered (P₀) and ordered (P₁, P₂)—prior to PbI₂ formation. When the appropriate solvated state of PbI₂ is exposed to MAI (methylammonium Iodide), it can lead to rapid and complete room temperature conversion into MAPbI₃ with higher quality films and improved solar cell performance. Complementary in‐situ optical reflectance, absorbance, and quartz crystal microbalance with dissipation (QCM‐D) measurements show that dry PbI₂ can take up only one third of the MAI taken up by the solvated‐crystalline P₂ phase of PbI₂, requiring additional annealing and yet still underperforming. The perovskite solar cells fabricated from the ordered P₂ precursor show higher power conversion efficiency (PCE) and reproducibility than devices fabricated from other cases. The average PCE of the solar cells is greatly improved from 13.2(±0.53)% (from annealed PbI₂) to 15.7(±0.35)% (from P₂) reaching up to 16.2%. This work demonstrates the importance of controlling the solvation of PbI₂ as an effective strategy for the growth of high‐quality perovskite films and their application in high efficiency and reproducible solar cells.     

Room‐Temperature Partial Conversion of α‐FAPbI3 Perovskite Phase via PbI2 Solvation Enables High‐Performance Solar Cells

The two‐step conversion process consisting of metal halide deposition followed by conversion to hybrid perovskite has been successfully applied toward producing high‐quality solar cells of the archetypal MAPbI₃ hybrid perovskite, but the conversion of other halide perovskites, such as the lower bandgap FAPbI₃, is more challenging and tends to be hampered by the formation of hexagonal nonperovskite polymorph of FAPbI₃, requiring Cs addition and/or extensive thermal annealing. Here, an efficient room‐temperature conversion route of PbI₂ into the α‐FAPbI₃ perovskite phase without the use of cesium is demonstrated. Using in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and quartz crystal microbalance with dissipation (QCM‐D), the conversion behaviors of the PbI₂ precursor from its different states are compared. α‐FAPbI₃ forms spontaneously and efficiently at room temperature from P₂ (ordered solvated polymorphs with DMF) without hexagonal phase formation and leads to complete conversion after thermal annealing. The average power conversion efficiency (PCE) of the fabricated solar cells is greatly improved from 16.0(±0.32)% (conversion from annealed PbI₂) to 17.23(±0.28)% (from solvated PbI₂) with a champion device PCE > 18% due to reduction of carrier recombination rate. This work provides new design rules toward the room‐temperature phase transformation and processing of hybrid perovskite films based on FA⁺ cation without the need for Cs⁺ or mixed halide formulation.     

Stable High‐Performance Perovskite Solar Cells via Grain Boundary Passivation

The trap states at grain boundaries (GBs) within polycrystalline perovskite films deteriorate their optoelectronic properties, making GB engineering particularly important for stable high‐performance optoelectronic devices. It is demonstrated that trap states within bulk films can be effectively passivated by semiconducting molecules with Lewis acid or base functional groups. The perovskite crystallization kinetics are studied using in situ synchrotron‐based grazing‐incidence X‐ray scattering to explore the film formation mechanism. A model of the passivation mechanism is proposed to understand how the molecules simultaneously passivate the Pb–I antisite defects and vacancies created by under‐coordinated Pb atoms. In addition, it also explains how the energy offset between the semiconducting molecules and the perovskite influences trap states and intergrain carrier transport. The superior optoelectronic properties are attained by optimizing the molecular passivation treatments. These benefits are translated into significant enhancements of the power conversion efficiencies to 19.3%, as well as improved environmental and thermal stability of solar cells. The passivated devices without encapsulation degrade only by ≈13% after 40 d of exposure in 50% relative humidity at room temperature, and only ≈10% after 24 h at 80 °C in controlled environment.     

Potentiating Hemorrhage in a Periadolescent Rat Model of Closed-Head Traumatic Brain Injury Worsens Hyperexcitability but Not Behavioral Deficits

Post-traumatic epilepsy (PTE) and neurocognitive deficits are devastating sequelae of head injuries that are common in adolescents. Investigating desperately needed treatments is hindered by the difficulties in inducing PTE in rodents and the lack of established immature rat models of pediatric PTE. Hemorrhage is a significant risk factor for PTE, but compared to humans, rats are less prone to bleeding because of their rapid blood coagulation system. In this study, we promoted bleeding in the controlled cortical impact (CCI) closed-head injury model with a 20 min pre-impact 600 IU/kg intraperitoneal heparin injection in postnatal day 35 (P35) periadolescent rats, given the preponderance of such injuries in this age group. Temporo-parietal CCI was performed post-heparin (HTBI group) or post-saline (TBI group). Controls were subjected to sham procedures following heparin or saline administration. Continuous long-term EEG monitoring was performed for 3 months post-CCI. Sensorimotor testing, the Morris water maze, and a modified active avoidance test were conducted between P80 and P100. Glial fibrillary acidic protein (GFAP) levels and neuronal damage were also assessed. Compared to TBI rats, HTBI rats had persistently higher EEG spiking and increased hippocampal GFAP levels (p < 0.05). No sensorimotor deficits were detected in any group. Compared to controls, both HTBI and TBI groups had a long-term hippocampal neuronal loss (p < 0.05), as well as contextual and visuospatial learning deficits (p < 0.05). The hippocampal astrogliosis and EEG spiking detected in all rats subjected to our hemorrhage-promoting procedure suggest the emergence of hyperexcitable networks and pave the way to a periadolescent PTE rat model.     

TILLING-by-Sequencing+ to Decipher Oil Biosynthesis Pathway in Soybeans: A New and Effective Platform for High-Throughput Gene Functional Analysis

Reverse genetic approaches have been widely applied to study gene function in crop species; however, these techniques, including gel-based TILLING, present low efficiency to characterize genes in soybeans due to genome complexity, gene duplication, and the presence of multiple gene family members that share high homology in their DNA sequence. Chemical mutagenesis emerges as a genetically modified-free strategy to produce large-scale soybean mutants for economically important traits improvement. The current study uses an optimized high-throughput TILLING by target capture sequencing technology, or TILLING-by-Sequencing⁺ (TbyS⁺), coupled with universal bioinformatic tools to identify population-wide mutations in soybeans. Four ethyl methanesulfonate mutagenized populations (4032 mutant families) have been screened for the presence of induced mutations in targeted genes. The mutation types and effects have been characterized for a total of 138 soybean genes involved in soybean seed composition, disease resistance, and many other quality traits. To test the efficiency of TbyS⁺ in complex genomes, we used soybeans as a model with a focus on three desaturase gene families, GmSACPD, GmFAD2, and GmFAD3, that are involved in the soybean fatty acid biosynthesis pathway. We successfully isolated mutants from all the six gene family members. Unsurprisingly, most of the characterized mutants showed significant changes either in their stearic, oleic, or linolenic acids. By using TbyS⁺, we discovered novel sources of soybean oil traits, including high saturated and monosaturated fatty acids in addition to low polyunsaturated fatty acid contents. This technology provides an unprecedented platform for highly effective screening of polyploid mutant populations and functional gene analysis. The obtained soybean mutants from this study can be used in subsequent soybean breeding programs for improved oil composition traits.     

Kinetic Stabilization of the Sol–Gel State in Perovskites Enables Facile Processing of High‐Efficiency Solar Cells

Perovskite solar cells increasingly feature mixed‐halide mixed‐cation compounds (FA_1?x?yMA_xCs_yPbI_3?zBr_z) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti‐solvent processing window for the fabrication of high‐quality films and efficient solar cells. This window widens from seconds, in the case of single cation/halide systems (e.g., MAPbI₃, FAPbI₃, and FAPbBr₃), to several minutes for mixed systems. In situ X‐ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol–gel and to the number of crystalline byproducts; the processing window therefore depends directly on the precise cation/halide composition. Moreover, anti‐solvent dripping is shown to promote the desired perovskite phase with careful formulation. The processing window of perovskite solar cells, as defined by the latest time the anti‐solvent drip yields efficient solar cells, broadened with the increasing complexity of cation/halide content. This behavior is ascribed to kinetic stabilization of sol–gel state through cation/halide engineering. This provides guidelines for designing new formulations, aimed at formation of the perovskite phase, ultimately resulting in high‐efficiency perovskite solar cells produced with ease and with high reproducibility.