Multiple defects renovation and phase reconstruction of reduced-dimensional perovskites via in situ chlorination for efficient deep-blue (454 nm) light-emitting diodes

Metal halide perovskites have demonstrated immense potential in light-emitting diodes (LEDs) due to their high color purity, tunable bandgap, and low fabrication costs. However, deep-blue LEDs, particularly those with emission wavelength below 460 nm (as compared to commercial GaN-based devices), still lag significantly in terms of optoelectronic performance. This limitation has become a major bottleneck in the commercialization of perovskite light-emitting diodes (PeLEDs) for full-color displays.

 

In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Jiaqi Zhu from National Key Laboratory of Science and Technology on Advanced Composites in Special Environments, Harbin Institute of Technology, China, and co-workers have proposed an in-situ chlorination (isCl) post-treatment method. This approach effectively regulated the phase distribution of mixed-halide quasi-2D perovskite films while comprehensively renovating both deep-state and shallow-state defects within the bulk and on the surface of the quasi-2D perovskites. As a result, it significantly enhanced the radiative recombination rate, exciton binding energy, and carrier transfer efficiency of the perovskites. The deep-blue PeLEDs achieved with this method demonstrated an external quantum efficiency (EQE) of 6.17%.

 

The authors first fabricated deep-blue PeLEDs using isCl method. After treatment, the electroluminescence (EL) emission peak of such devices shifted from 461 nm (without treatment) to 454 nm, with a maximum EQE of 6.17% and a peak brightness of 510 cd m⁻². Notably, the EL peak position remained unchanged during device operation. Furthermore, the authors observed that the treated deep-blue PeLEDs exhibited faster carrier transport and increased recombination rates, as well as enhanced operational stability.

 

The authors conducted a series of experiments and density functional theory (DFT) calculations to investigate the mechanism by which the isCl treatment enhances the optoelectronic performance of quasi-2D perovskite films. During the isCl treatment, the released chloride ions simultaneously renovated halide vacancies within the bulk and on the surface of the quasi-2D perovskites, contributing to an enlarged bandgap and a blue-shifted emission. Additionally, the C=O groups in the p-FCA molecules generated during the isCl treatment bonded with undercoordinated lead, effectively renovating shallow-state defects. Meanwhile, the -OH groups in p-FCA interacted with halide ions to suppress the formation of lead-halide antisite defects, thereby addressing deep-state defects.

 

The isCl treatment induced changes in the crystal orientation and phase structure of the quasi-2D perovskites. The strong interaction between the fluorine atoms in p-FCA and organic cations hindered the incorporation of organic cations to the lead-halide frameworks during nucleation and crystallization. This effectively suppressed the formation of small-n phases, reconstructing the phase structure of such films, thereby enhancing carrier transfer and suppressing non-radiative recombination.

 

This study proposed a novel method to simultaneously renovate both deep-state and shallow-state defects in quasi-2D perovskites and reconstruct the phase structure. By strong interactions with the components in precursor during the isCl post-treatment process, the exciton binding energy and carrier transport efficiency of the quasi-2D perovskite films were significantly improved. This advancement boosted the efficiency of deep-blue PeLEDs and contributed to the development of full-color displays using PeLEDs.

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