Pure Red Light-Emitting Diodes Based on Quantum Confined Quasi-Two-Dimensional Perovskites with Cospacer Cations

Efficient and spectrally stable pure-red perovskite light-emitting diodes (PeLEDs) are still rare and urgently needed for high-definition display. The traditional color tuning method by varying halide composition undergoes phase segregation and has spectral instability issues. Instead of halide mixing, we fabricate pure-red PeLEDs based on quasi-two-dimensional (quasi-2D) perovskites by simultaneously incorporating phenethylammonium (PEA) and 1-naphthylmethylammonium (NMA) cations. The control of PEA and NMA cospacer ratio modulates the phase distribution and the resulting different color emission. The PeLEDs with PEA:NMA molar ratio of 5:5 exhibit a pure-red (635 nm) electroluminescence (EL) with a CIE coordinate (0.709, 0.285) approaching the Rec. 2020 specification. Meanwhile, the optimized devices exhibit an external quantum efficiency (EQE) of 12.41% and a maximum brightness of 1452.6 cd m^–2, which are among the best-performing pure-red PeLEDs based on quasi-2D perovskite to date. Additionally, our PeLEDs demonstrate stable EL spectra under different operating voltages and continuous operation.