Nanostructure Modification on Thermally Evaporated Perovskite Films Toward Large-Area Light-Emitting Diodes

In the contemporary era of digital society, there is a rising demand for vibrant color displays applicable in wearable electronics, indoor lighting, and expansive display systems. Metal halide perovskites have emerged as a highly promising material due to their advantages such as cost-effectiveness, excellent color purity with narrow full width at half maximum (FWHM, ~20nm), and the ease of color tuning by altering halide components. Nonetheless, despite the high-efficiency perovskite light-emitting diodes (PeLEDs) with external quantum efficiency (EQE) of over 20% was achieved through facile spin-coating methods, it couldn’t be applied to the fabrication of large-area devices due to the low uniformity of the film. To overcome these limitations, a thermal evaporation method utilizing all-inorganic 3D CsPbBr₃ powders as precursor was developed. However, their use as emitters showed poor emission efficiency arising from critical drawbacks such as large crystal size, low exciton binding energy, and high defect concentration.<br/>In this study, we introduced a new thermal evaporation method by co-evaporating 3D CsPbBr₃ and bulky ammonium cation (benzylammonium bromide, BzABr) to achieve quasi-two-dimensional (quasi-2D) perovskites with energy funneling and strong charge confinement. The existence of quasi-2D perovskites with efficient charge funneling and quantum confinement was confirmed by optical analysis. The grain size was also reduced from 80 to 50 nm, which could induce additional spatial charge confinement for efficient radiative recombination. Compared to the pristine 3D CsPbBr₃film, the quasi-2D perovskite film showed tenfold-increased photoluminescence (PL) intensity. PeLEDs based on the thermally-evaporated quasi-2D perovskite thin films showed a maximum current efficiency of 3.6 cd/A and a maximum luminance of 1700 cd/m², showing an considerable improvement than that of Compared to PeLEDs based on thermally-evaporated 3D CsPbBr₃ without light emission due to the low luminous efficiency and high leakage current, PeLEDs based on the thermally-evaporated quasi-2D perovskite thin films showed a maximum current efficiency of 3.6 cd/A and a maximum luminance of 1700 cd/m², showing the great possibility of efficient PeLEDs based on thermal evaporation method. . This work represents a significant advancement towards the commercialization of metal halide perovskites for future vivid color displays by successfully addressing a critical challenge in the fabrication of large-area perovskite-based display devices.