Room-temperature synthesis of perovskite-phase CsPbI3 nanocrystals for optoelectronics via a ligand-mediated strategy

Cesium lead iodide (CsPbI3) perovskite nanocrystals (NCs) have received widespread attention in light-emitting diodes (LEDs), solar cells, and photodetectors (PDs) for their high thermal stability resulting from all-inorganic components. However, the facile room-temperature synthesis of perovskite-phase CsPbI3 NCs remains a major challenge because of the thermal unequilibrium-induced metastable (black) to stable (yellow) phase transition. Here, we proposed a ligand-mediated strategy to synthesize γ-phase CsPbI3 perovskite NCs in non-polar solvent at room temperature for the first time. We found that the introduction of 4-dodecylben-zenesulfonic acid (DBSA) ligand could prevent CsPbI3 changing from the γ phase to the δ phase, which was attributed to the strong bonding and steric hindrance that suppressed the distortion of the corner-sharing octahedron. The as-synthesized CsPbI3 perovskite NCs were well-dispersed in organic solvents (such as toluene and hexane), which could serve as inks to construct the active layer for solution-processed optoelectronic devices (The PD with an on/off ratio of 200, and the LED showing an external quantum efficiency (EQE) approaching 6%). The proposed method showed superior universality as evidenced by the successful synthesis of efficient red-greenblue CsPbX3 NCs (the EQEs were 8.6%, 14.7%, and 3.4% for red, green, and blue LEDs, respectively). The results demonstrated that the room-temperature synthesis could avoid the tediousness of typical hot-injection at high temperatures and this method could be widely applied to various optoelectronic devices.