Lead-free germanium halide perovskite WLEDs with enhanced luminescence efficiency and ultra-stability through atomic-level regulation and resin encapsulating by 3D printing

This work starts with the "functional motif" and regulates lead-free perovskite materials at the molecular level by combining density functional theory (DFT) calculations and high- throughput techniques, aiming to simultaneously address the toxicity, luminescence efficiency, and stability issues of perovskite materials. As expected, the optimized geometric structures, band structures, and density of states of CsGeBr3:Ln3+ were successfully obtained by assembling the [Ge1-xLnxBr6] functional motifs using DFT techniques. With increasing Ln3+ concentrations, the functional [Ge1-xLnxBr6] motifs tend to localize and increases the local electron density of Br, which is beneficial for improving the luminescence properties. Subsequently, CsGeBr3:Ln3+ with enhanced luminescence were prepared and further encapsulated into photosensitive resins using 3D printing technology to improve the luminescence stability. Based the results of DFT calculation and high-throughput technology, ultra- stable white light-emitting diodes (WLEDs) with excellent performance have been successfully achieved. After being placed for six months, the luminescence intensity and spectral shape of the resin coated sample remain unchanged. The corresponding international commission on illumination (CIE) coordinates the best sample are (0.3207, 0.3285), with a low color rendering index (Ra) of 96 and a correlated color temperature (CCT) of 6083 K. This work provides new insights and ideas for improving the luminescence intensity and stability of lead-free perovskite WLEDs by combining machine learning and 3D printing technology.