Doping-Enhanced Short-Range Order of Perovskite Nanocrystals for Near-Unity Violet Luminescence Quantum Yield

Abstract

All-inorganic perovskite nanocrystals (NCs) have emerged as a new generation of low-cost semiconducting luminescent system for optoelectronic applications. The room-temperature photoluminescence quantum yields (PLQYs) of these NCs in the green and red spectral range approach unity. However, their PLQYs in the violet are much lower, and an insightful understanding of such poor performance remains missing. We report a general strategy for the synthesis of all-inorganic violet-emitting perovskite NCs with near-unity PLQYs through engineering local order of the lattice by nickel ion doping. A broad range of experimental characterizations, including steady-state and time-resolved luminescence spectroscopy, X-ray absorption spectra, and magic angle spinning nuclear magnetic resonance spectra, reveal that the low PLQY in undoped NCs is associated with short-range disorder of the lattice induced by intrinsic defects such as halide vacancies and that Ni doping can substantially eliminate these defects and result in increased short-range order of the lattice. Density functional theory calculations reveal that Ni doping of perovskites causes an increase of defect formation energy and does not introduce deep trap states in the band gap, which is suggested to be the main reason for the improved local structural order and near-unity PLQY. Our ability to obtain violet-emitting perovskite NCs with near-perfect properties opens the door for a range of applications in violet-emitting perovskite-based devices such as light-emitting diodes, single-photon sources, lasers, and beyond.

Recent advances and prospects toward blue perovskite materials and light‐emitting diodes

“…Hence, the stability and PLQY are obviously enhanced by reducing the defect state density and passivating grain boundaries, leading to excellent optoelectronic properties for devices constructed by using the doped perovskites as active layers . Typically, various metal ions, including Bi 3+ , Ni 2+ , Mn 2+ , Cu 2+ , Zn 2+ , Cd 2+ and rare earth ions (eg, Ce 3+ , Er 3+ , Yb 3+ ), have been doped into halide perovskites. In the halide perovskite system, the similar bond energy between doped elements with X and Pb‐X is considered to be one of the key factors that favors impurity incorporation …”

“…These defects may deteriorate the short‐range order of the lattice and act as trapping centers of photo‐generated carriers, such as vacancies or distorted [PbX 6 ] octahedra on the surface and inside the perovskite. Yong et al proposed a nickel (Ni) doping strategy for the synthesis of CsPbCl 3 NCs, which can effectively passivate these defects and achieve a near‐unity PLQY.…”

“…88 Copyright 2018 American Chemical Society perovskite. Yong et al 84 proposed a nickel (Ni) doping strategy for the synthesis of CsPbCl 3 NCs, which can effectively passivate these defects and achieve a near-unity PLQY.…”

Metal halide perovskite nanocrystals and their applications in optoelectronic devices

“…Doping has been proved to be an effective way to improve the optoelectronic and magnetic properties of II‐VI/III‐V semiconductor NCs, which has been adopted for perovskite NCs . Sun's group synthesized Ni 2+ ‐doped CsPbCl 3 QDs with enhanced PL QY to near unity, which is attributed to the increased formation energy of defects and no deep trap states . Kovalenko's group let Pb(acetate) 2 and FA‐acetate react with OA in ODE and injected oleylammonium bromide (OAmBr) at 130°C to synthesize FAPbBr 3 QDs.…”

“…[87][88][89] Sun's group synthesized Ni 2+ -doped CsPbCl 3 QDs with enhanced PL QY to near unity, which is attributed to the increased formation energy of defects and no deep trap states. 90 Kovalenko's group let Pb(acetate) 2 and F I G U R E 3 A. Illustration of various modes of relaxation of charge carriers produced on photoexcitation of the perovskites.…”