Enhanced stability of lead-free double perovskite Cs2Na1−xBi1−xMn2xCl6 microcrystals and their optoelectronic devices under high humidity environment by SiO2 encapsulation

The current studies on lead-free double perovskites (DPs) have mainly focused on the optimization of their optical properties, while less attention has been paid to their optical stability under high humidity environment. However, optoelectronic devices will inevitably be exposed to high humidity environment in practical applications so that investigating the optical stability of lead-free DPs under high humidity environment will be especially important for its subsequent development. We prepared lead-free DP Cs2Na1−xBi1−xMn2xCl6 microcrystals (MCs) with different Mn2+ content by the solution method at room temperature, where the photoluminescence quantum yield (PLQY) of Cs2Na0.8Bi0.8Mn0.4Cl6 MCs achieved a maximum of 22.3% with 20% doping of Mn2+, subsequently tested for stability under high humidity environment. The results indicated that the structure and fluorescence properties of Cs2Na0.8Bi0.8Mn0.4Cl6 MCs were destroyed after being contacted with water molecules and that Cs2Na0.8Bi0.8Mn0.4Cl6 MCs was subsequently restored again by using hydrochloric acid solution, but its fluorescence was not able to reach initial intensity, which severely affected its application under high humidity environment. Therefore, the encapsulation of Cs2Na0.8Bi0.8Mn0.4Cl6 MCs using water stable and highly transparent SiO2 was proposed to obtain Cs2Na0.8Bi0.8Mn0.4Cl6@SiO2 core-shell MCs, its optical properties were unaffected after stored in aqueous solution for 10 days. The assembled light emitting diode devices kept constant illumination output in harsh environment of 85% relative humidity, which laid a solid foundation for the subsequent development of lead-free DP optoelectronic devices.