Modification of mixed-halide quasi-2D perovskites by aminophylline towards efficient and spectrally stable blue light-emitting diodes with low efficiency roll-off

Abstract

During the past few years, significant progress has been achieved with blue perovskite light-emitting diodes (PeLEDs) based on quasi-two-dimensional (quasi-2D) perovskites with chloride (Cl) and bromine (Br) ions toward improving their external quantum efficiencies (EQEs). However, mixed-halide quasi-2D PeLEDs still suffer from serious efficiency roll-off and spectral instability. Here, modification of mixed-Cl/Br quasi-2D perovskites with a multi-functional additive is proposed to achieve efficient blue PeLEDs with reduced efficiency roll-off and stable electroluminescence (EL) spectra. Aminophylline (AMP) with Lewis base characteristics was employed as the additive to incorporate with the CsPb(Cl/Br)₃ based quasi-2D perovskites. It was observed that the introduction of the AMP additive suppressed the low dimensional phases in the quasi-2D blue perovskite film, leading to the carriers being harvested for radiative recombination rather than being located at the low dimensional phases. In addition, the AMP additive, containing carbonyl and imine groups, can coordinate with the uncoordinated Pb²⁺, which enables the passivation of defects and the reduction of trap-assisted non-radiative recombination in the blue quasi-2D perovskite films. As a result, based on the AMP-modified quasi-2D perovskites, the champion PeLED achieved a maximum EQE of 13.2% with a stable EL peak at 484 nm, which is 1.6 times that of the pristine device without the AMP additive. Importantly, the AMP-modified blue PeLEDs maintained an EQE as high as 11.5% at a high luminance of 1000 cd m⁻², demonstrating a significantly reduced EQE roll-off. Meanwhile, the AMP-modified devices presented more stable spectra than the pristine devices under various voltages or continuous operation at an identical initial luminance. This study demonstrated a facile modification strategy by using a multi-functional additive to facilitate the improvement of efficiency roll-off and spectral stability in mixed-Cl/Br quasi-2D blue PeLEDs.