2D/quasi-2D Dion-Jacobson perovskites for light emitting applications

Abstract

Recently, low-dimensional perovskites have attracted increasing attention. Compared to the 3D counterparts, the quasi-2D perovskites exhibit improved stability under harsh environmental conditions due to the incorporation of the hydrophobic organic spacers. The formed multiple-quantum-wells structure prevents the diffusion of moisture and oxygen into the interior and benefits the light emission accounting for the confinement effect and the resulting large exciton binding energy. Simply through composition engineering and dimensional engineering, the blue to deep blue color emission can be achieved. Thereby the 2D/quasi-2D perovskites have been considered a promising candidate for the next generation of light-emitting diodes (LEDs). However, the blue PeLEDs exhibit worse performance than the green and red, considering the deterioration of perovskites, phase segregation, mismatched charge transport layers, and unbalanced electron−hole injection. Dion–Jacobson (DJ) phase 2D/quasi-2D perovskites are expected to demonstrate improved efficiency and stability. However, the studies of DJ phase PeLEDs are ultra-rare. Here, the DJ phase perovskites with sky-blue emission were obtained through the incorporation of different types of ligand cations, and their optical properties related to the phase distribution were discussed. Thereafter the hole transport layers for controlled hole injection and balanced charge recombination were developed. The final DJ phase sky-blue PeLED with improved performance was obtained. In addition, perovskites face a critical issue: the toxic Pb can severely contaminate the environment and damage human health. To tackle the barrier, Tin (Sn) has been explored as an alternative for the replacement of Pb. However, the poor stability of Sn2+ will lead to the formation of self-doping background and vacancy defects detrimental to perovskite stability and the corresponding device’s performance. Hence, the DJ phase spacer HDA was introduced to form the low-dimensional Sn-perovskites (both film and powder) for the optical properties and stability investigation. The process of phase transformation from 2D HDASnBr4 to 1D HDA3SnBr8(H2O) phase during the ambient exposure was revealed, and the humidity-dependent optical properties were discovered. To further improve the stability, additives were induced in both HDA Sn-perovskite films and powder to achieve extended lifetimes.