Room-temperature synthesis of triple-cation green perovskite quantum dots for optoelectronic applications

The development of multi-cation perovskite quantum dots (PQDs) is limited by the low availability of fitting A-site cations due to the unsuitable radii of a large gamut of amine cations. The impact of oversized or undersized cations on the perovskite structure is detrimental to the structural stabilization and electroluminescence efficiency of the PQDs. Researchers are actively seeking suitable-sized cations to mitigate perovskite defect formation and optimize charge carrier confinement within the PQDs. In contrast to cesium (Cs) or formamidine (FA), which are exposed to degradation pathways, guanidinium (GA)-doping has been to provide a suitable radius and the lack a dipole moment. The triple nitrogen functionality of GA enables it to passivate both the PbBr₆ octahedra and surface defects through vacant A-sites and entropically stabilize the perovskite. Furthermore, the insertion of GA into the PQD lattice is enthalpically facilitated by the presence and arrangement of smaller Cs and Br atoms. Herein, we have synthesized a Cs-FA PQD reference into which GA is doped via two chemical routes. Our triple-cation system exhibits substantially improved optical properties and was applied for the fabrication of a PeLED device. The optimized triple-cation PQDs-based PeLED device exhibited an external quantum efficiency of 5.87% and a luminescence of 13726 cd m^-2.