Band Gap Engineering toward Wavelength Tunable CsPbBr3 Nanocrystals for Achieving Rec. 2020 Displays

For next-generation high-definition displays, the newly recommendation 2020 (Rec. 2020) standard calls for the emission wavelength of green emitters to be kept at 525–535 nm with narrow emission line width below 25 nm. All-inorganic lead halide perovskite CsPbBr3 nanocrystals (NCs) with sharp emission seem as the prefect one to match the call, however, it is a great challenge to tune their emission wavelength to the target window of 525–535 nm because of the intrinsic band gap of CsPbBr3. Herein, we report a facile strategy to prepare CsPbBr3 NCs with finely tunable emissions in the narrow range of 525–535 nm by establishing a CsPbBr3–Cs4PbBr6:Na Type II structure. The doping of the Na ions is the key factor to construct the Type II structure, which induces the formation of the Cs4PbBr6:Na phase and builds CsPbBr3–Cs4PbBr6:Na Type II structure, leading to the tunable emission wavelength of CsPbBr3 NCs. The as-synthesized CsPbBr3 NCs exhibit an ideal emission at 525–535 nm with a narrow emission line width of 23 nm and a high photoluminescence quantum yield (PLQY) of 85%. As a green downconverter, an ultrapure green backlight covers 97% of the Rec. 2020 standard in the CIE 1931 color space, representing the "greenest" backlight up to now.