Spacer cation engineering in Ruddlesden-Popper perovskites for efficient red light-emitting diodes with recommendation 2020 color coordinates

•The chemical structures of spacer cations in Ruddlesden-Popper perovskites significantly affect the film properties, including phase distribution, energy funneling process, trap density, and carrier mobility.•The POEA-based RPP films show narrow phase distribution, efficient energy funneling, and low trap density.•The POEA-based red PeLEDs achieve the best device performance with a peak EQE of 10.3%, a maximum brightness of 1052 cd m−2, Rec. 2020 color coordinates of (0.71, 0.29), and excellent spectral stability.