Ligand-Assisted Sulfide Surface Treatment of CsPbI₃ Perovskite Quantum Dots to Increase Photoluminescence and Recovery

Abstract

CsPbI3 perovskite quantum dots (QDs) are more unstable over time as compared to other perovskite QDs, owing to ligand loss and phase transformation. The strong red emission from fresh CsPbI3 QDs gradually declines to a weak emission from aged QDs, which PLQY dropped by 93% after a 20 day storage; finally, there is no emission from δ-phase CsPbI3. The present study demonstrated a facile surface treatment method, where a sulfur–oleylamine (S-OLA) complex was utilized to passivate the defect-rich surface of the CsPbI3 QDs and then self-assembly to form a matrix outside the CsPbI3 QDs protected the QDs from environmental moisture and solar irradiation. The PLQY of the treated CsPbI3 QDs increased to 82.4% compared to initial value of 52.3% of the fresh QDs. Furthermore, there was a significant increase in the colloidal stability of the CsPbI3 QDs. Above 80% of the original PLQY of the treated QDs was reserved after a 20 day storage and the black phase could be maintained for three months before transforming to the yellow phase. The introduction of S-OLA induced the recovery of the lost photoluminescence of the nonluminous aged CsPbI3 QDs with time to 95% of that of the fresh QDs. Furthermore, the photoluminescence was maintained for one month. The increase in the stability and photoluminescence are critical for realizing high-performance perovskite-QD-based devices. Therefore, this work paves the way for increasing the performance of perovskite-based devices in the near future.

High Efficiency and Narrow Emission Band Pure-Red Perovskite Colloidal Quantum Wells

“…High color saturation is an important indicator for judging whether the luminescent materials can be used in ultra-high-definition displays. And the PL peak of the CsPbI 3 CQWs with n = 4 is located at 626 nm with a narrow emission band of 28 nm, which is narrower than the emission bandwidth of the CsPbI 3 nanocrystals reported so far. − The CIE coordinates (0.69, 0.31) meet the requirements for red emission (0.708, 0.292) in the Rec. 2020 standard.…”

Can Sulfur-Containing Small Systems Enhance the Photoluminescence and Stability of the Blue-, Green- and Yellow-Emitting Perovskite Nanocrystals? A Case Study with Sodium Thiosulfate

“… Interestingly, the binding energy of the Br 3d 5/2 core level spectra is also blue-shifted by ∼0.7 eV in the treated NCs (Figure S10b). This indicates that the electron density around the central Pb 2+ cation is impacted by the formation of the Pb–S bonds, leading to an adjustment in chemical bonding between Pb 2+ and Br – in the lead bromide octahedral units of the treated NCs, which in turn strengthens the Pb–Br bonds, causing a shift of the Br 3d XPS peak at higher energy. − Like in EDX measurements, here also the calculated Br/Pb ratio in treated CsPbBr 3 NCs is found to be slightly lower than that in as-synthesized CsPbBr 3 NCs (Table S2). The sulfur content obtained from XPS measurements is however found to be slightly higher to that obtained from EDX studies (Table S2).…”

Atomic Insights of Stable, Monodispersed CsPbI3−xBrx (x = 0, 1, 2, 3) Nanocrystals Synthesized by Modified Ligand Cell

“…We did not observe any noticeable change in the peak position of the binding energy of corresponding atoms indicating their same chemical oxidation states but the peak position gets slightly changed mainly due to the change of chemical environment. [ 44 ] The elemental XPS spectra of CsPbI 3 , CsPbBr 2 I CsPbBrI 2 and CsPbBr 3 are shown in Figure S13 and corresponding peak positions are tabulated in Table ST1 (Supporting Information). The calculated atomic ratio of all the halide perovskites is tabulated in Table ST2 (Supporting Information).…”

“…An improved short circuit current for CsPbI 2 Br device also supports the reduced defect state density resulting in an enhanced charge transport behavior. As it is well known that iodine loss, ligand loss in CsPbI 3 under ambient condition is a common phenomenon, [ 59,44 ] which creates some nonradiative electrical defects on the surface of the film, hampering the charge transport in the device. As a result, we have observed a lower J sc value for the CsPbI 3 device as compared to the CsPbI 2 Br one.…”