  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, 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.
