Metal-halide perovskite solar cells combine high photovoltaic efficiency with low-temperature solution processing, but their performance and durability remain sensitive to precursor coordination, nucleation, drying, grain-boundary formation, and interfacial degradation. This critical narrative review evaluates plant-derived secondary metabolites as process-active additives rather than assuming that biological origin alone confers sustainability or passivation. Evidence is organized for alkaloids and xanthines, polyphenols and phenolic acids, and terpenoids and carotenoids, with explicit separation of experimentally demonstrated mechanisms, computational support, molecular analogy, and design hypotheses. Carbonyl-mediated coordination provides the clearest mechanistic basis for caffeine and related xanthines, whereas selected phenolic compounds have been associated, in separate studies, with coordination, crystallization control, and suppression of Sn²⁺ oxidation. Direct photovoltaic evidence now includes selected monoterpenoids, the sesquiterpene lactone artemisinin, and carotenoids, although the results remain molecule- and process-specific and do not justify class-wide generalization. The review maps molecular descriptors onto precursor chemistry, coating and crystallization variables, film structure, recombination, ion migration, device performance, and stability. Translation beyond laboratory spin coating will require specification-controlled additives, standardized stability protocols, process-compatible formulations, and iterative computational–experimental screening. This evidence-based framework identifies secondary-metabolite scaffolds as a promising but molecule-specific platform for perovskite process engineering, whose sustainability benefit remains to be established through life-cycle assessment.

Thermoset-like polymer composites based on poly(glycidyl methacrylate) (PGMA) functionalized by post-polymerization CO₂ cycloaddition were synthesized and reinforced with varying contents of pecan nut shell (PNS, 10–30 wt%) as a lignocellulosic filler. The CO₂ fixation step, which converts the pendant epoxide groups of PGMA into pendant five-membered cyclic carbonates, was promoted by a new Ni(bpy)₃-templated hybrid lead bromide of empirical formula [Ni(bpy)₃Pb₃Br₈·(DMF)₂], whose crystal structure was solved by single-crystal X-ray diffraction. The resulting materials were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). FTIR confirmed the partial conversion of epoxide groups into cyclic carbonates (ν =1794 and 1270 cm⁻¹) and the incorporation of the lignocellulosic phase. TGA showed a shift of the maximum decomposition temperature toward higher values (up to 418 °C in PGMA–CO₂–PNS) compared to neat PGMA, consistent with restricted segmental mobility imparted by the cyclic carbonate units and PNS filler. DSC revealed an upward shift of the glass transition and the suppression of melting transitions, supporting the formation of a crosslinked, thermoset-like network. SEM micrographs evidenced effective dispersion of PNS within the matrix and improved interfacial continuity at higher filler loadings. Overall, the combination of CO₂ valorization through cyclic-carbonate functionalization and lignocellulosic reinforcement provides an accessible route to sustainable thermoset-like composites with enhanced thermal stability, suitable for applications with low structural demands.