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Abstract Functional macromolecular materials promise to enable important improvements in many aspects of everyday life, including for energy applications, novel electronics systems, or wearable health care products. In contrast to widely‐used commodity plastics such as polyolefins, polyamides, or polyesters, it, however, remains challenging to advance detailed insights into the interrelation of structure and performance for functional polymers, limiting progress. The reason is that the macroscopic properties of such polymers often depend on local chain arrangements rather than long‐range order only. Here, it is demonstrated on the example of the well‐investigated ferroelectric poly(vinylidene fluoride) (PVDF) that modern nuclear magnetic resonance (NMR) spectroscopy enables thequantitativeanalysis of the complex solid‐state structure of this polymer, providing unprecedented insight. The precise fractions of chain segments of different conformations are revealed, as well as their spatial distributions with respect to each other. Thereby, a significant population of short‐range ordered chain segments is identified, a large fraction of which in close proximity to defects and disordered segments. Unsurprisingly, different environments lead to different structural dynamics — collectively showing that characterizing local order/disorder and their dynamics is imperative to accurately describe the properties of functional polymers such as PVDF. 

Ruddlesden–Popper perovskites (RPPs) are promising materials for optoelectronic devices. While iodide‐based RPPs are well‐studied, the crystallization of mixed‐halide RPPs remains less explored. Understanding the factors affecting their formation and crystallization are vital for optimizing morphology, phase purity, and orientation, which directly impact device performance. Here, we investigate the crystallization and properties of mixed‐halide RPPs (PEA)₂FA_n−1Pb_n(Br_1/3I_2/3)_3n + 1(PEA = C₆H₅(CH₂)₂NH₃⁺and FA = CH(NH₂)₂⁺) (n = 1, 5, 10) using DMSO ((CH₃)₂SO) or NMP (OC₄H₆NCH₃) as cosolvents and MACl (MA = CH₃NH₃⁺) as an additive. For the first time, the presence of planar defects in RPPs is directly observed by in situ grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) and confirmed through the simulation of the patterns that matched the experimental. GIWAXS data also reveals that DMSO promotes higher crystallinity and vertical orientation, while MACl enhances crystal quality but increases halide segregation, shown here by nano X‐ray fluorescence (nano‐XRF) experiments. For low‐n RPPs, orientation is crucial for solar cell efficiency, but its impact decreases with increasing n. Our findings provide insights into optimizing mixed‐halide RPPs, guiding strategies to improve crystallization, phase control, and orientation for better performance not only in solar cells but also in other potential optoelectronic devices.