Bright Tail States in Blue-Emitting Ultrasmall Perovskite Quantum Dots

Abstract

All-inorganic lead halide perovskite quantum dots (CsPbBr QDs) are attracting significant research interests because of their highly efficient light-emitting performance combined with tunable emission wavelength facilely realized by ion exchange. However, blue emission from perovskite QDs with strong quantum confinement is rarely reported and suffers from lower luminescence efficiency. Here we report blue-emitting ultrasmall (∼3 nm) CsPbBr QDs with photoluminescence (PL) quantum yield as high as 68%. Using time-resolved and steady-state PL spectroscopy, we elucidate the mechanism of the highly efficient PL as recombination of excitons localized in radiative band tail states. Through analyzing the spectral-dependent PL lifetime and the PL line shape, we obtain a large band tail width of ∼80 meV and a high density of state of ∼10 cm. The relaxation of photocarriers into the radiative tail states suppresses the capture by nonradiative centers. Our results provide solid evidence for the positive role of band tail states in the optical properties of lead halide perovskites, which can be further tailored for high-performance optoelectronic devices.

Surface Halogen Compensation for Robust Performance Enhancements of CsPbX3 Perovskite Quantum Dots

“…This result is confirmed by the sharper absorption edge of the modified CsPbBr 3 QDs (Figure S7, Supporting Information) . Although the obvious edge state/absorption edge is not always detrimental to exciton recombination in inorganic HPQDs, they affect the PLQY of the CsPbBr 3 QDs . In other words, the surface V Br defects in the pristine CsPbBr 3 QDs act as trap states and significantly inhibit the radiative recombination.…”

Ultrafast Thermodynamic Control for Stable and Efficient Mixed Halide Perovskite Nanocrystals

“…[ 31,37–39 ] Since the synthesis of CsPbX 3 NCs by high temperature thermal injection was proposed in 2015, [ 40 ] almost all attention has been paid to varying the synthesis temperature, reaction time, surface ligands, or controlling the amount of reactants. [ 10,24,41 ] However, the research on how to stop the high‐temperature chemical reaction quickly to obtain high crystallinity and uniform grain size has not been well researched, and the ice‐water is widely used cooling medium at present. While, the lowest temperature of ice‐water is only 0 °C and the cooling ratio is limited.…”

“…[ 5,6 ] However, the PLQY of blue‐emitting perovskite has struggled to match this such admirable value. [ 7–11 ] This exceedingly unbalanced development of three primary colors triggered by the low blue photoluminescence efficiency seriously hinders the further practical application of perovskite. [ 12–14 ] Although recent remarkable efforts have been devoted to remedy this regret, [ 15–18 ] at present, it is generally recognized that achieving high blue emitting PLQY with stable and pure spectra is challenging.…”

In Situ Passivation of PbBr64– Octahedra toward Blue Luminescent CsPbBr3 Nanoplatelets with Near 100% Absolute Quantum Yield

“…13−15 However, it is worth noting that CsPbBr 3 NCs with small size usually exhibit large emission width due to enormous defects, which also results in a low QY. 14 Besides, unstable morphology with time will also influence the peak position and emission line widths, which means specific morphology treatments are in demand to avoid aggregation or ripening. 16 Although NCs with hybrid halogens (Cl and Br) can also exhibit narrow blue emissions, the unavoidable phase separation induced peak shift and its associated formation of traps are also limitations for achieving high QYs with long-term stability.…”