The high photoluminescence efficiency, color purity, extended gamut, and solution processability make low-dimensional hybrid perovskites attractive for light-emitting diode (PeLED) applications. However, controlling the microstructure of these materials to improve the device performance remains challenging. Here, the development of highly efficient green PeLEDs based on blends of the quasi-2D (q2D) perovskite, PEA₂Cs₄Pb₅Br₁₆, and the wide bandgap organic semiconductor 2,7 dioctyl[1] benzothieno[3,2-b]benzothiophene (C₈-BTBT) is reported. The presence of C₈-BTBT enables the formation of single-crystal-like q2D PEA₂Cs₄Pb₅Br₁₆ domains that are uniform and highly luminescent. Combining the PEA₂Cs₄Pb₅Br₁₆:C₈-BTBT with self-assembled monolayers (SAMs) as hole-injecting layers (HILs), yields green PeLEDs with greatly enhanced performance characteristics, including external quantum efficiency up to 18.6%, current efficiency up to 46.3 cd A⁻¹, the luminance of 45 276 cd m⁻², and improved operational stability compared to neat PeLEDs. The enhanced performance originates from multiple synergistic effects, including enhanced hole-injection enabled by the SAM HILs, the single crystal-like quality of the perovskite phase, and the reduced concentration of electronic defects. This work highlights perovskite:organic blends as promising systems for use in LEDs, while the use of SAM HILs creates new opportunities toward simpler and more stable PeLEDs.