Scalable Synthesis of Lead-Free Tetramethylammonium Manganese Halides for Highly Efficient Backlight Displays

Lead-free halides have emerged as clean candidates for lighting and display applications because of their superior optoelectronic properties and environmental friendliness. As for the commercialization, the simple synthetic process, scaled production, low-cost, and excellent performance are the upmost factors. In this work, lead-free tetramethylammonium manganese halides are quantitatively synthesized using a mechanochemical approach, in which [(CH3)4N]2MnCl4 powders show green emission with a photoluminescence quantum yield (PLQY) of 21% and (CH3)4NMnCl3 powders possess red emission with a PLQY of 51%, arising from the intrinsic 4T1(4G) & RARR; 6A1(6S) d-d transition of Mn2+. To further boost the green emission efficiency, the composition engineering strategies by Br/Cl substitution and excess organic halide compensation are developed, achieving a high PLQY of 98% for the obtained [(CH3)4N]2MnBr4 powders. Furthermore, white light emitting diode (WLED) devices are fabricated by combining green [(CH3)4N]2MnBr4 powders with red (CH3)4NMnCl3 powders or single crystals, which exhibit a high luminous efficacy (98.06 or 142.40 lm W-1), wide color gamut (over 100 % of NTSC in CIE 1931), and good operating stability (maintained above 80% efficiency after 176 h). This work suggests ball-milling as a mass synthesis method for metal halides and provides a new Mn2+-based phosphor for white LEDs in backlight display applications. Lead-free metal halides are clean candidates for future lighting and displays. A facile, scalable, and eco-friendly ball-milling method is presented to obtain tetramethylammonium manganese halides. The [(CH3)4N]2MnBr4 have a near-unity green emission efficiency and can be combined with (CH3)4NMnCl3 red emitters to fabricate light emitting diodes, achieving a maximum luminous efficacy of 142.40 lm W-1 and wide color gamut of 100% NTSC.image