Electroluminescence efficiencies and stabilities of quasi-two-dimensional halide perovskites are restricted by the formation of multiple-quantum-well structures with broad and uncontrollable phase distributions. Here, we report a ligand design strategy to substantially suppress diffusion-limited phase disproportionation, thereby enabling better phase control. We demonstrate that extending the π-conjugation length and increasing the cross-sectional area of the ligand enables perovskite thin films with dramatically suppressed ion transport, narrowed phase distributions, reduced defect densities, and enhanced radiative recombination efficiencies. Consequently, we achieved efficient and stable deep-red light-emitting diodes with a peak external quantum efficiency of 26.3% (average 22.9% among 70 devices and cross-checked) and a half-life of ~220 and 2.8 h under a constant current density of 0.1 and 12 mA/cm², respectively. Our devices also exhibit wide wavelength tunability and improved spectral and phase stability compared with existing perovskite light-emitting diodes. These discoveries provide critical insights into the molecular design and crystallization kinetics of low-dimensional perovskite semiconductors for light-emitting devices.

Perovskite solar cells (PSCs) have delivered a power conversion efficiency (PCE) of more than 25% and incorporating polymers as hole‐transporting layers (HTLs) can further enhance the stability of devices toward the goal of commercialization. Among the various polymeric hole‐transporting materials, poly(triaryl amine) (PTAA) is one of the promising HTL candidates with good stability; however, the hydrophobicity of PTAA causes problematic interfacial contact with the perovskite, limiting the device performance. Using molecular side‐chain engineering, a uniform 2D perovskite interlayer with conjugated ligands, between 3D perovskites and PTAA is successfully constructed. Further, employing conjugated ligands as cohesive elements, perovskite/PTAA interfacial adhesion is significantly improved. As a result, the thin and lateral extended 2D/3D heterostructure enables as‐fabricated PTAA‐based PSCs to achieve a PCE of 23.7%, improved from the 18% of reference devices. Owing to the increased ion‐migration energy barrier and conformal 2D coating, unencapsulated devices with the new ligands exhibit both superior thermal stability under 60 °C heating and moisture stability in ambient conditions.

High energy density lithium–sulfur batteries (LSBs) are a potential replacement for lithium-ion batteries (LIBs). However, practical lifetimes are inhibited by lithium polysulfide (LiPS) shuttling. Concurrently, plastic waste accumulation worldwide threatens our ecosystems. Herein, a fast and facile strategy to upcycle polyethylene terephthalate (PET) waste into useful materials is investigated. Dilithium terephthalate (Li₂TP) and dipotassium terephthalate (K₂TP) salts were synthesized from waste soda bottles via microwave depolymerization and solution coated onto glass fiber paper (GFP) separators. Salt-functionalized separators with Li₂TP@GFP and K₂TP@GFP mitigated LiPS shuttling and improved electrochemical performance in cells. Pore analysis and density functional theory (DFT) calculations indicate the action mechanism is synergistic physical blocking of bulky LiPS anions in nanopores and diffusion inhibition via electrostatic interactions with abundant carboxylate groups. LSBs with K₂TP@GFP separator showing highest LiPS affinity and smallest pore size demonstrated enhanced initial capacity as compared to non-modified GFP by 5.4% to 648 mAh g⁻¹, and increased cycle 100 capacity by 23% to 551 mAh g⁻¹. Overall, K₂TP@GFP retained 85% of initial capacity after 100 cycles with an average capacity fading of 0.15% per cycle. By comparison, GFP retained only 73% of initial capacity after 100 cycles with 0.27% average capacity loss, demonstrating effective LiPS retention.

Organic-inorganic hybrid perovskite semiconductors are under investigation for many applications owing to their excellent optoelectronic properties and relatively simple processing. Two-dimensional (2D) halide perovskites are an attractive class of hybrid perovskites that have additional optoelectronic tunability due to their accommodation of relatively large organic ligands. Nevertheless, contemporary ligand design depends on either expensive trial-and-error testing of whether a ligand can be integrated within the lattice or conservative heuristics that unduly limit the scope of ligand chemistries. Here, the structural determinants of ligand incorporation and perovskite stability are established by molecular dynamics (MD) simulations of over ten thousand perovskites, including an algorithmically generated set of prospective ligand chemistries and all previously reported experimental primary ammonium ligands based on C, H, O, S, and N. The simulation results show near-perfect predictions of positive and negative literature examples, predict trade-offs between several ligand features and perovskite stability, and ultimately predict an inexhaustibly large 2D-compatible ligand design space. This dataset is used to train machine learning classifiers capable of predicting the geometric stability of perovskite structures based solely on generalizable ligand features, thus providing an inexpensive tool for screening putative ligands. As a demonstration, the model was used to down-select five new ligands that were successfully synthesized and incorporated into 2D perovskites. This work provides a new paradigm for future low-dimensional perovskite design.