Kim and co-workers report systematical studies with methylammonium chloride (MACl) in formamidinium lead iodide (FAPbI 3 )-based perovskite thin films. The MACl addition could induce the intermediate phase with pure a-phase without annealing, effectively stabilizing the structure, only through cationic site substitution. The film quality can be significantly improved, exhibiting a 63 increase in grain size, a 33 increase in phase crystallinity, and a 4.33 increase in photoluminescence lifetime. The resulting optimized solar cells achieved a peakscan efficiency of above 24%.

Further improvement and stabilization of perovskite solar cell (PSC) performance are essential to achieve the commercial viability of next-generation photovoltaics. Considering the benefits of fluorination to conjugated materials for energy levels, hydrophobicity, and noncovalent interactions, two fluorinated isomeric analogs of the well-known hole-transporting material (HTM) Spiro-OMeTAD are developed and used as HTMs in PSCs. The structure–property relationship induced by constitutional isomerism is investigated through experimental, atomistic, and theoretical analyses, and the fabricated PSCs feature high efficiency up to 24.82% (certified at 24.64% with 0.3-volt voltage loss), along with long-term stability in wet conditions without encapsulation (87% efficiency retention after 500 hours). We also achieve an efficiency of 22.31% in the large-area cell.

Hard carbon is the most promising anode material for sodium‐ion batteries and potassium‐ion batteries owing to its high stability, widespread availability, low‐cost, and excellent performance. Understanding the carrier‐ion storage mechanism is a prerequisite for developing high‐performance electrode materials; however, the underlying ion storage mechanism in hard carbon has been a topic of debate because of its complex structure. Herein, it is demonstrated that the Li+‐, Na+‐, and K+‐ion storage mechanisms in hard carbon are based on the adsorption of ions on the surface of active sites (e.g., defects, edges, and residual heteroatoms) in the sloping voltage region, followed by intercalation into the graphitic layers in the low‐voltage plateau region. At a low current density of 3 mA g–1, the graphitic layers of hard carbon are unlocked to permit Li+‐ion intercalation, resulting in a plateau region in the lithium‐ion batteries. To gain insights into the ion storage mechanism, experimental observations including various ex situ techniques, a constant‐current constant‐voltage method, and diffusivity measurements are correlated with the theoretical estimation of changes in carbon structures and insertion voltages during ion insertion obtained using the density functional theory.

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