Steric Effects in Ruddlesden–Popper Blue Perovskites for High Quantum Efficiency

Abstract

bandgap and low-cost fabrication. Methylammonium (MA) lead halide perovskites, in particular, have drawn much attention as promising materials for next-generation light-emitting diodes (LEDs). In the past 5 years, the external quantum efficiency (EQE) of light-emitting MA perovskite LEDs has increased from <1% to >20% in green, red, and IR spectral ranges. [1][2][3][4][5] However, strategies to fabricate blueemitting Ruddlesden-Popper perovskites (RPPs) typically require to halide substitutions, which result in unstable mixtures that undergo halide phase segregation, and yielding spectrally unstable blue-emitting LEDs. [6][7][8][9] RPPs are layered, quasi-twodimensional structures whose lattices are sliced by two layers of organic spacer cations bound to the (100)-orientated lead bromide octahedra. Their chemical composition is (L) 2 MA n−1 Pb n X 3n+1 , where L is a spacer cation that separates the layers and induces quantum and dielectric confinement. Quasi-2D perovskites with the spacer cation PEA, (PEA) 2 (MA) n−1 Pb n X 3n+1 , have been demonstrated to Ruddlesden-Popper perovskites (RPPs) feature enhanced stability compared to their bulk counterparts and attract attention for potential applications in light-emitting diodes (LEDs). However, to date, blue-emitting RPPs rely on halide compositional tuning, resulting in spectral shifts due to halide segregation under photo-/electrical-excitation. Here, efficient blue-emitting materials with single-halide RPPs using organic spacer engineering are reported. Experimental and computational results show that the (110)-oriented thin films exhibit larger bandgap and enhanced stability regardless of the choice of spacers, relative to the (100)-oriented RPPs. The correlation between the lattice structures and optoelectronic properties reveals that this new class of RPPs exhibits sky-blue emission at 483 nm with a quantum efficiency of ≈62%. Spearman correlation between the steric size of the spacers and the bandgap is estimated to be 92%, showing that the steric effect is crucial influencers. The protocol and strategy established in this study can be exploited to develop blue perovskite LEDs.

Two-dimensional complex metal halides: influence of restricted dimensionality on functional properties

“…These include studies on red emissions, [110][111][112] green emissions, 93,113 and blue emissions. [114][115][116] Blue RP phase emitters, however, lag behind their red and green counterpart mainly due to increased electron-phonon coupling and trap-mediated non-radiative recombination, less efficient energy transfer, and interface uorescence quenching. 117,118 We will begin our discussion by examining a select few signicant works from the initial stages of RP phase research as LEDs.…”