Unique Photoelectric Properties and Defect Tolerance of Lead-Free Perovskite Cs3Cu2I5 with Highly Efficient Blue Emission

Alkylammonium Halides for Phase Regulation and Luminescence Modulation of Cesium Copper Iodide Nanocrystals for Light-Emitting Diodes

All-inorganic cesium copper halide nanocrystals have attracted extensive attention due to their cost-effectiveness, low toxicity, and rich luminescence properties. However, controlling the synthesis of these nanocrystals to achieve a precise composition and high luminous efficiency remains a challenge that limits their future application. Herein, we report the effect of oleylammonium iodide on the synthesis of copper halide nanocrystals to control the composition and phase and modulate their photoluminescence (PL) quantum yields (QYs). For CsCu2I3, the PL peak is centered at 560 nm with a PLQY of 47.3%, while the PL peak of Cs3Cu2I5 is located at 440 nm with an unprecedently high PLQY of 95.3%. Furthermore, the intermediate-state CsCu2I3/Cs3Cu2I5 heterostructure shows white light emission with a PLQY of 66.4%, chromaticity coordinates of (0.3176, 0.3306), a high color rendering index (CRI) of 90, and a correlated color temperature (CCT) of 6234 K, indicating that it is promising for single-component white-light-emitting applications. The nanocrystals reported in this study have excellent luminescence properties, low toxicity, and superior stability, so they are more suitable for future light-emitting applications.

Recent Advances and Opportunities of Eco-Friendly Ternary Copper Halides: A New Superstar in Optoelectronic Applications

Recently, the newly-emerging lead-free metal-halide materials with less toxicity and superior optoelectronic properties have received wide attention as the safer and potentially more robust alternatives to lead-based perovskite counterparts. Among them, ternary copper halides (TCHs) have become a vital group due to their unique features, including abundant structural diversity, ease of synthesis, unprecedented optoelectronic properties, high abundance, and low cost. Although the recent efforts in this field have made certain progresses, some scientific and technological issues still remain unresolved. Herein, a comprehensive and up-to-date overview of recent progress on the fundamental characteristics of TCH materials and their versatile applications is presented, which contains topics such as: i) crystal and electronic structure features and synthesis strategies; ii) mechanisms of self-trapped excitons, luminescence regulation, and environmental stability; and iii) their burgeoning optoelectronic devices of phosphor-converted white light-emitting diodes (WLEDs), electroluminescent LEDs, anti-counterfeiting, X-ray scintillators, photodetectors, sensors, and memristors. Finally, the current challenges together with future perspectives on the development of TCH materials and applications are also critically described, which is considered to be critical for accelerating the commercialization of these rapidly evolving technologies.

A ligand strategy retarding monovalent copper oxidation toward achieving Cs3Cu2I5 perovskite emitters with enhanced stability for lighting

0D copper-based perovskites (Cs3Cu2I5) have fascinating optical properties, such as strong exciton binding energy, high photoluminescence quantum yield (PLQY) and large Stokes shifts from self-trapped excitons (STEs), which make them highly considerable candidates in the field of lighting. However, the stability of Cs3Cu2I5 is compromised by the oxidation of Cu+ to Cu2+ during the storage or operation process. Here, we proposed a ligand engineering strategy to improve the stability of Cs3Cu2I5via an organic molecule (ethylenediaminetetraacetic acid, EDTA) with multiple functional groups. The strong interaction between carboxyl groups and Cu+ was evidenced through FTIR and XPS, and it could retard monovalent copper oxidation. After storing for 90 days, the EDTA-engineered Cs3Cu2I5 (EDTA-Cs3Cu2I5) maintained its original crystalline structure, while the control Cs3Cu2I5 exhibited an impurity phase. Through quantitative analysis, the content of Cu2+ in EDTA-Cs3Cu2I5 was found to be 83.9% lower than that in control Cs3Cu2I5. Benefiting from the inhibition of Cu+ oxidation, EDTA-Cs3Cu2I5 exhibited improved light emission stability. For example, the optimized EDTA-Cs3Cu2I5 retained 74.7% of the initial photoluminescence (PL) intensity after 90-day storage under ambient conditions, while the pure Cs3Cu2I5 retained only 41.7%. Furthermore, EDTA could passivate defects and enhance the PL properties of the optimized Cs3Cu2I5, which showed a PLQY of 94.7%, much higher than that of 71.4% for pure Cs3Cu2I5. We further constructed a WLED based on the EDTA-engineered Cs3Cu2I5, which showed CIE at (0.3238, 0.3354), a CRI of 91.7, and a T50 of 361 h. The proposed EDTA ligand strategy provides a new way to regulate the light-emitting properties and stabilities of Cs3Cu2I5 for future industrialization.

Pressure Regulating Self-Trapped States toward Remarkable Emission Enhancement of Zero-Dimensional Lead-Free Halides Nanocrystals

Copper(I)-based halides have recently attracted increasing attention as a substitute for lead halides, owing to their nontoxicity, abundance, unique structure, and optoelectric properties. However, exploring an effective strategy to further improve their optical activities and revealing structure-optical property relationships still remain a great concern. Here, by using high pressure technique, a remarkable enhancement of self-trapped exciton (STE) emission associated with the energy exchange between multiple self-trapped states in zero-dimensional lead-free halide Cs₃ Cu₂ I₅ NCs is successfully achieved. Furthermore, high-pressure processing endows the piezochromism of Cs₃ Cu₂ I₅ NCs by experiencing a white light and a strong purple light emission, which is able to be stabilized at near-ambient pressure. The distortion of [Cu₂ I₅ ] clusters composing of tetrahedral [CuI₄ ] and trigonal planar [CuI₃ ] and the decreased Cu-Cu distance between the adjacent Cu-I tetrahedron and triangle are responsible for the significant STEs emission enhancement under high pressure. The experiments combined with first-principles calculations not only shed light on the structure-optical property relationships of [Cu₂ I₅ ] clusters halide, but also provide guidance for improving emission intensity that is highly desirable in solid-state lighting applications.

Lead-free all-inorganic halide double perovskite materials for optoelectronic applications: progress, performance and design

The geometrical and electronic structures of all-inorganic halide double perovskites and their applications in optoelectronic devices are reviewed. Novel design methods are desirable to develop this type of perovskite with superior performance.