Highly Stable All-Inorganic Perovskite Quantum Dots Using a ZnX2-Trioctylphosphine-Oxide: Application for High-Performance Full-Color Light-Emitting Diode

Abstract

Perovskite is a very promising material that is being extensively studied at the bulk and nanosize scales because it has outstanding optical properties, including high quantum efficiency and narrow emission spectra. However, perovskite has stability issues related to heat, air, and light. To overcome these, highly stable perovskite quantum dots (PeQDs) are developed using excess Zn precursor and trioctylphosphine-oxide (TOPO). In particular, it is clarified that Zn and TOPO are combined and these complexes are attached to the surface of the PeQDs through 31P NMR. They not only have high quantum efficiency and sharp full width at half maximum values (15–30 nm) but also have improved long-term stability at high temperature. Additionally, XPS measurements are conducted for a detailed surface analysis of PeQDs, finding that the TOPO-Zn complex effectively decrease PbO bonding in the lattice. Perovskite full-color electroluminescence (EL) devices are fabricated using PeQDs and 9,9-bis[4-[(4-ethenylphenyl)methoxy]phenyl]-N2,N7-di-1-naphthalenyl-N2,N7-diphenyl-9H-fluorene-2,7-diamine (VB-FNPD) as a new cross-linkable hole transporting material. The VB-FNPD has a high-hole carrier mobility compared to the PVK as conventional hole-transporting layer. As a result of EL performance, they have high EQE (%) and current efficiency (Cd A−1) of (7.12%, 9.93 Cd A−1) for red, (6.06%, 32.5 Cd A−1) for green, and (0.56%, 0.88 Cd A−1) for blue-emitting devices, respectively.