Highly Luminescent Violet- and Blue-Emitting Stable Perovskite Nanocrystals

Abstract

Among the lead halide perovskites, photoluminescence quantum yield (PLQY) of violet-emitting CsPbCl3 nanocrystals (NCs) is the lowest (<5%). This is an impediment to the development of perovskite-based materials for optical applications covering the entire visible region. While PLQY of the green- and red-emitting perovskites of this class has been raised to near-unity, achieving a similar level for violet- and blue-emitting NCs is still quite challenging. Herein, we report a novel method of simultaneously passivating the surface defects and crystal disorder of violet-emitting CsPbCl3 NCs to dramatically enhance (by a factor of ∼120) the PLQY and stability without affecting the peak wavelength (403 nm) and full-width at half-maximum (FWHM) of the photoluminescence (PL) band. We show that the addition of the correct quantity of CuCl2 during the hot-injection synthesis of CsPbCl3 NCs leads to doping of Cu+ into the NCs, which rectifies octahedral distortion of the crystal and the Cl– passivates the surface; the combined influence of the two results in huge PL enhancement. NCs emitting throughout the blue region (430-460 nm) with near-unity PLQY (92%–98%) can then be obtained by partial halide-exchange of the doped sample. Femtosecond transient absorption studies suggest suppression of the ultrafast carrier trapping process in doped NCs. The results help extending the utility of these materials in optical applications by covering the violet–blue region as well.

Recent Advances in Blue Perovskite Quantum Dots for Light‐Emitting Diodes

“…Thus, supernumerary halogen source should be added to optimize the halogen distribution. For example, Park et al employed tetraoctylammonium bromide (TOAB) and tetrahexylammonium chloride (THAC) as both ligands and halogen [75] Copyright 2019, American Chemical Society. b) LARP method.…”

“…[114] On the other hand, due to the smaller radii of Cl − ions, Cl − substitution increases the local structural deformation, resulting in high halide trap density inside the PQDs. [75] Generally, most PQDs are defect tolerant and the defects seem to show little influence on the PL performance. Nevertheless, as an exception, the Cl vacancies are not completely benign.…”

“…In a similar mechanism, Cu 2+ ions were also employed to optimize the shortrange order and the best PL QY was up to 60%. [75] Alkali metal ions with the same valence and similar ionic radius to Cs + are good alternatives to replace Cs + . The introduction of K + and Rb + into CsPbCl 3 PQDs has been reported, [142,144] and an improved PL QY over 10% at 408 nm was demonstrated.…”

All‐Inorganic Halide Perovskite Nanocrystals: Future Prospects and Challenges to Go Lead Free

“…[130][131][132][133] Even for some cases PLQY may attain values near unity as a result of the efficient energy transfer from the perovskite NC host to other varieties of metal-ion dopants, such as Ni 2þ , Cd 2þ , Ca 2þ , Sr 2þ , Na þ , Ce 3þ , and Sb 3þ can augment PLQY without introducing new emission lines. [134][135][136][137][138] Chen et al [138] have explored the effect of alkaline earth metal doping statistics. e) Stabilized power output and f ) EQE spectrum of the "champion" PSC device.…”

“…[ 130–133 ] Even for some cases PLQY may attain values near unity as a result of the efficient energy transfer from the perovskite NC host to other varieties of metal‐ion dopants, such as Ni 2+ , Cd 2+ , Ca 2+ , Sr 2+ , Na + , Ce 3+ , and Sb 3+ can augment PLQY without introducing new emission lines. [ 134–138 ] Chen et al [ 138 ] have explored the effect of alkaline earth metal doping in CsPbCl 3 NCs. They observed a significant increase in PLQY from 0.8% in the pristine sample to 36.6% (Mg 2+ doping), to 50.7% (Sr 2+ doping), and to 77% (Ca 2+ doping).…”