Enhancement of photoluminescence and the stability of CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals with phthalimide passivation

Cesium lead halide perovskite nanocrystals (CsPbX3 NCs) have been the flourishing area of research in the field of photovoltaic and optoelectronic applications because of their excellent optical and electronic properties. However, they suffer from low stability and deterioration of photoluminescence (PL) properties post-synthesis. In this work, we demonstrate that incorporating an additional ligand can further enhance the optical properties and stability of NCs. Here, we introduced phthalimide as a new surface passivation ligand into the oleic acid/oleylamine system in situ to get near-unity photoluminescence quantum yield (PLQY) of CsPbBr3 and CsPbI3 perovskite NCs. Phthalimide passivation dramatically improves the stability of CsPbCl3, CsPbBr3, and CsPbI3 NCs under ambient light and UV light. The PL intensity was recorded for one year, which showed a dramatic improvement for CsPbBr3 NCs. Nearly 11% of PL can be retained even after one year with phthalimide passivation. CsPbCl3 NCs exhibit 3 times higher PL with phthalimide and retain 12% PL intensity even after two months, while PL of as-synthesized NCs completely diminishes. Under continuous UV light illumination, the PL intensity of phthalimide passivated NCs is well preserved, while the as-synthesized NCs exhibit negligible PL emission in 2 days. About 40% and 25% of initial PL is preserved for CsPbBr3 and CsPbCl3 NCs in the presence of phthalimide. CsPbI3 NCs with phthalimide exhibit PL even after 2 days, while PL for as-synthesized NCs rapidly declined in the first 10 h. The presence of phthalimide in CsPbI3 NCs could maintain stability even after a week, while the as-synthesized NCs underwent a transition to the non-luminescent phase within 4 days. Furthermore, blue, green, yellow, and red-emitting diodes using CsPbCl1.5Br1.5, CsPbBr3, CsPbBr1.5I1.5, CsPbI3 NCs, respectively, are fabricated by drop-casting NCs onto blue LED lights, which show great potential in the field of display and lighting technologies.