In order to obtain deep-red perovskite light-emitting diodes (LEDs) with high color purity, high luminous efficiency, and simple preparation method, Ethylammonium iodide (EAI) is selected as an organic additive. EAI is doped in CsPbBr0.5I2.5 perovskite precursor solution with the solvent of N’N-dimethylformamide (DMF). In this method, spin-coating is used without using anti-solvent to obtain perovskite films with different EAI doping ratios. It is found that when the doping molar ratio is 0.5∶1 (EAI∶Pb2+), a flat and compact perovskite film is obtained, and the perovskite grains after passivation are reduced to 40 nm. Based on this perovskite film as the light-emitting layer, a deep-red perovskite LED with the structure of ITO (90 nm)/ PVK (30 nm)/ perovskite (40 nm)/ TPBi (55 nm)/ CsF (1.2 nm)/ Al (120 nm) was fabricated, giving a turn-on voltage of 2.7 V, a maximum luminance of 320 cd/m2, a maximum external quantum efficiency (EQE) of 7 %, and a bright red electroluminescence peak of 680 nm with a Commission Internationale del′Eclairage (CIE) coordinates of (0.71, 0.28). Therefore, the organic additive EAI can effectively inhibit the growth of large perovskite grains while reducing the density of defect states. Simple solution processing technology and molecular-scale self-assembly technology are used to obtain high-quality thin films for preparing excellent deep-red perovskite LED.