Lead-Free Halide Perovskites and Perovskite Variants as Phosphors toward Light-Emitting Applications

Abstract

Lead halide perovskites have attracted tremendous research interests in the light-emitting field because of their high defect tolerance, solution processability, tunable spectrum, and efficient emission. In terms of luminescence types, both the narrowband emission derived from free-exciton (FE) and broadband white light emission from self-trapped exciton (STE) show great advantages in light-emitting applications. Despite the fascinating characteristics, their commercialization still suffers from the presence of toxic lead (Pb) and unsatisfactory stability. In this spotlight, we mainly focus on the lead-free candidates as phosphors for possible light-emitting applications. Thanks to the chemical diversity of metal halide perovskites and perovskite variants, many excellent lead-free light-emitting materials have recently been synthesized and characterized. We first classify these materials into three types according to material structures, including (1) double perovskites A2B­(I)­B­(III)­X6, (2) vacancy ordered perovskites A2B­(IV)­X6, (3) miscellaneous perovskite variants or halide semiconductors, which refer to halides without clear relation to the perovskite structure. We then highlight the importance of electronic dimensionality, defect passivation, and impurity doping in developing highly efficient perovskite-based emitters. We also discuss their applications in white light-emitting diodes (W-LED). Further challenges toward practical applications and potential applications are also included in a section on outlook and future challenges.

Strongly Emissive Lead‐Free 0D Cs3Cu2I5 Perovskites Synthesized by a Room Temperature Solvent Evaporation Crystallization for Down‐Conversion Light‐Emitting Devices and Fluorescent Inks

“…Strong emission feature of the sample is essential for lighting and displays. PL QYs of the Cs 3 Cu 2 I 5 crystals and powder samples were determined to be 89% and 60%, respectively, under excitation wavelength of 310 nm, which is well comparable to previously reported values for lead‐free 0D perovskite materials 58. PL spectra (Figure 3d) measured at different excitation wavelengths ranging from 290 to 330 nm give same position of a rather broad peak at 442 nm.…”

“…It is noteworthy that the PLE peak position is located at 310 nm which belongs to ultraviolet B (UVB) region (290–320 nm); thus the Cs 3 Cu 2 I 5 sample is suitable for practical use as a phosphor in UV pumped down‐conversion LEDs. Moreover, the reduced self‐absorption due to the large Stokes shift (132 nm) of Cs 3 Cu 2 I 5 is also favorable for its use in lighting 58…”

All‐Inorganic Lead‐Free 0D Perovskites by a Doping Strategy to Achieve a PLQY Boost from <2 % to 90 %

“…All‐inorganic zero‐dimensional (0D) lead halide perovskites with isolated octahedron have attracted extensive attention for optoelectronic applications . Nevertheless, the toxicity and instability of lead perovskite pose a threat to the ecological environment and humans, hindering their further development . Thus, searching for the less toxic or nearly non‐toxic and highly stable lead‐free perovskite becomes an effective solution.…”

A Lead‐Free All‐Inorganic Metal Halide with Near‐Unity Green Luminescence

“…Recently low‐dimensional lead‐free metal halides have been reported to exhibit highly efficient emission via facile solution processing. [ 12–21 ] In particular for yellow and blue light‐emission, the photoluminescence quantum yield (PLQY) has reached near‐unity in some zero‐dimensional (0D) Sn‐based and Cu‐based halide compounds. [ 19,22–26 ] However, to our knowledge, for another one of the three primary colors of light, the PLQY of the reported lead‐free green‐light emitting metal halides, especially all‐inorganic semiconductors, is far behind the performance of lead halide perovskites.…”