Thermally stable ethylammonium doping strategy for pure red emission in CsPbI₃ quantum dot light-emitting diodes

All-inorganic CsPbI₃ quantum dots (QDs) exhibit remarkable optoelectronic properties, identifying them as promising candidates for advanced display materials. However, achieving pure-red emission from CsPbI₃ QDs remains a significant challenge due to limitations in bandgap tuning using conventional high-temperature hot-injection methods. Introducing A-site cations, such as ethylammonium (EA⁺), has been shown to modulate near-edge states by inducing lattice distortions. Nevertheless, the thermal instability of EA⁺ salts at high temperatures poses a major obstacle in achieving stable doping. To address this challenge, we harnessed the acid-base equilibrium between ethylammonium salts and oleic acid in the cesium precursor, enabling the in situ formation of thermally stable ethylammonium oleate. This innovation allowed the precise tuning of the emission wavelength within 630-650 nm by controlling EA⁺ doping levels. After optimization of the EA⁺ doping concentration and device architecture, pure-red perovskite light-emitting diodes were achieved with an external quantum efficiency up to 26.1%. Our findings present a groundbreaking methodology for bandgap engineering of CsPbI₃ QDs, providing pivotal insights for the development of advanced perovskite optoelectronic materials and devices.