Impact of Processing on Structural and Compositional Evolution in Mixed Metal Halide Perovskites during Film Formation

Understanding crystallization processes and their pathways in metal‐halide perovskites is of crucial importance as this strongly affects the film microstructure, its stability, and device performance. While many approaches are developed to control perovskite formation, the mechanisms of film formation are still poorly known. Using time‐resolved in situ grazing incidence wide‐angle X‐ray scattering, the film formation of perovskites is investigated with average stoichiometry Cs_0.15FA_0.85PbI₃, where FA is formamidinium, using the popular antisolvent dropping and gas jet treatments and this is contrasted with untreated films. i) The crystallization pathways during spin coating, ii) the subsequent postdeposition thermal annealing, and iii) crystallization during blade coating are studied. The findings reveal that the formation of a nonperovskite FAPbI₃ phase during spin coating is initially dominant regardless of the processing and that the processing treatment (e.g., antisolvent dropping, gas jet) has a significant impact on the as‐cast film structure and affects the phase evolution during subsequent thermal treatment. It is shown that blade coating can be used to overcome the nonperovskite phase formation via solvothermal direct crystallization of perovskite phase. This work shows how real‐time investigation of perovskite formation can help to establish processing–microstructure–functionality relationships.     

Revealing the Perovskite Film Formation Using the Gas Quenching Method by In Situ GIWAXS: Morphology,Properties, and Device Performance

The optoelectronic properties, morphology, and consequently the performance of metal halide perovskite solar cells are directly related to the crystalline phases and intermediates formed during film preparation. The gas quenching method is compatible with large-area deposition, but an understanding of how this method influences these properties and performance is scarce in the literature. Here, in situ grazing incidence wide angle X-ray scattering is employed during spin coating deposition to gain insights on the formation of MAPbI₃ and Cs_xFA_1−xPb(I_0.83Br_0.17)₃ perovskites, comparing the use of dimethyl sulfoxide (DMSO) and 2-methyl-n-pyrrolidone (NMP) as coordinative solvents. Intermediates formed using DMSO depend on the perovskite composition (e.g., Cs content), while for NMP the same intermediate [PbI₂(NMP)] is formed independently on the composition. For MAPbI₃ and Cs_xFA_1−xPb(I_0.83Br_0.17)₃ with a small amount of Cs (10% and 20%), the best efficiencies are achieved using NMP, while the use of DMSO is preferred for higher (30% and 40%) amount of Cs. The inhibition of the 2H/4H hexagonal phase when using NMP is crucial for the final performance. These findings provide a deep understanding about the formation mechanism in multication perovskites and assist the community to choose the best solvent for the desired perovskite composition aiming to perovskite-on-silicon tandem solar cells.     

In Situ Observation of Crystallization Dynamics and Grain Orientation in Sequential Deposition of Metal Halide Perovskites

Metal halide perovskites have revolutionized the development of highly efficient, solution‐processable solar cells. Further advancements rely on improving perovskite film qualities through a better understanding of the underlying growth mechanism. Here, a systematic in situ grazing‐incidence X‐ray diffraction investigation is performed, facilitated by other techniques, on the sequential deposition of formamidinium lead iodide (FAPbI₃)‐based perovskite films. The active chemical reaction, composition distribution, phase transition, and crystal grain orientation are all visualized following the entire perovskite formation process. Furthermore, the influences of additive ions on the crystallization speed, grain orientation, and morphology of FAPbI₃‐based films, along with their photovoltaic performances, are fully evaluated and optimized, which leads to highly reproducible and efficient perovskite solar cells. The findings provide key insights into the perovskite growth mechanism and suggest the fabrication of high‐quality perovskite films for widespread optoelectronic applications.     

In Situ Photosynthesis of an MAPbI3/CoP Hybrid Heterojunction for Efficient Photocatalytic Hydrogen Evolution

Halide perovskite like methylammonium lead iodide perovskite (MAPbI₃) with its prominent optoelectronic properties has triggered substantial concerns in photocatalytic H₂ evolution. In this work, to attain preferable photocatalytic performance, a MAPbI₃/cobalt phosphide (CoP) hybrid heterojunction is constructed by a facile in situ photosynthesis approach. Systematic investigations reveal that the CoP nanoparticle can work as co‐catalyst to not only extract photogenerated electrons effectively from MAPbI₃ to improve the photoinduced charge separation, but also facilitate the interfacial catalytic reaction. As a result, the as‐achieved MAPbI₃/CoP hybrid displays a superior H₂ evolution rate of 785.9 µmol h^?1 g^?1 in hydroiodic acid solution within 3 h, which is ≈8.0 times higher than that of pristine MAPbI₃. Furthermore, the H₂ evolution rate of MAPbI₃/CoP hybrid can reach 2087.5 µmol h^?1 g^?1 when the photocatalytic reaction time reaches 27 h. This study employs a facile in situ photosynthesis strategy to deposit the metal phosphide co‐catalyst on halide perovskite nanocrystals to conduct photocatalytic H₂ evolution reaction, which may stimulate the intensive investigation of perovskite/co‐catalyst hybrid systems for future photocatalytic applications.     

In Situ Formation of Conductive Metal Sulfide Domain in Metal Oxide Matrix: An Efficient Way to Improve the Electrochemical Activity of Semiconducting Metal Oxide

A new effective way to improve the electrochemical activity of semiconducting metal oxide is developed by the in situ formation of conductive metal sulfide domain in the metal oxide matrix. The Li_0.96Ti_1.08S₂?Li₄Ti₅O₁₂ nanocomposites with tunable compositions and electrical properties are synthesized by the reaction of Li₄Ti₅O₁₂ with CS₂ at elevated temperature. The resulting incorporation of conductive Li_0.96Ti_1.08S₂ domain in the Li₄Ti₅O₁₂ matrix is effective in enhancing the electrical conductivity and electrode activity of semiconducting lithium titanate. As anode materials for lithium ion batteries, the obtained Li_0.96Ti_1.08S₂?Li₄Ti₅O₁₂ nanocomposites show much greater discharge capacity and better rate characteristics than does the pristine Li₄Ti₅O₁₂. The usefulness of the present method is further evidenced from the improvement of the electrochemical activity of semiconducting CsTi₂NbO₇ after the reaction with CS₂. The present study clearly demonstrates the in situ formation of conductive metal sulfide domain using CS₂ liquid can provide an efficient and universal way to improve the electrode functionality of semiconducting metal oxide.     

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.     

Liberating the Electrolyte via In Situ Conversion of an Amide,Sulfonate-Containing Monomer Precursor for High-Temperature Graphite/NCM Batteries

High-temperature (HT) operation and storage performance of Li-ion batteries (LIBs) are essential for applications in electric vehicles, grid storage, or defense missions. Unfortunately, severe capacity fading is witnessed due to growing instability of the electrode/electrolyte interphase at HT. Herein, the study liberates the electrolyte from the task of film-formation. Instead, it takes advantage of the favorable solid-electrolyte interphase (SEI)-forming functional groups by priorly anchoring them on graphite surface. Specifically, via molecular design, unsaturated CC bond, together with amide and sulfonate groups, are concurrently involved, namely the lithium-2-acrylamido-2-methyl-1-propanesulfonate (Li-AMPS). Upon electrochemical cycle, the unsaturated CC bond in Li-AMPS turns into a radical that induces polymerization between CC bonds to construct a polymeric network. The presence of amide and sulfonate groups endows the SEI with nitrogen, sulfur-based reduction products OSO₂Li and Li₃N, etc. As such, the designed interphase makes the use of propylene carbonate-based electrolyte possible. By assembling full cells with the modified graphite and LiNi_0.5Co_0.2Mn_0.3O₂ (cathode loading of ≈18.5 mg cm⁻²), the capacity retention of the full cell has increased from 53.2% (with pristine graphite) to 77.8% after 300 cycles under 60 °C. A 2 Ah, 265 Wh kg⁻¹ pouch cell is also able to operate for 200 cycles at an extreme temperature of 80 °C with the modified graphite.