Plasma-Treated CsPbBr₃ Nanocrystal Films for Anticounterfeiting Applications

Abstract

Lead halide perovskite (LHP) nanocrystals (NCs) are considered propitious materials due to their extraordinary optoelectronic properties. Their poor ambient stability hinders their practical applications. Among the several approaches taken to enhance the ambient stability, plasma treatment is considered one of the best approaches because it does not hinder charge transport or reduce relative NC content while allowing easy and scalable processing. The plasma treatment increases the overall ambient stability of LHPs but at the cost of photoluminescence quantum yield (PLQY). We found that a short duration of the plasma treatment enhances the PL intensity by 30%, along with enhanced moisture stability. However, longer duration of plasma treatment decreases the photoluminescence (PL), and the NCs become hydrophilic. In this work, we report the underlying chemistry of stability enhancement during plasma treatment and how it affects the PL intensity. We performed Ar−O 2 plasma treatment on the CsPbBr 3 NCs thin films, which induces the cross-linking of the passivating ligand oleylamine that creates a stronger network of ligands, providing better encapsulation and higher PL intensity. A longer duration of plasma treatment results in oxidation of the passivating ligands in the presence of oxygen that eventually degrades the NCs. We created double-layer fluorescent security tags using the PL-stabilized NCs and as-synthesized NCs, having the same emission profile. The security pattern was created using the stabilized perovskite and masked with the assynthesized perovskite, which is relatively unstable and can be washed off under certain treatments.

Hybrid Ligand Polymerization for Weakly Confined Lead Halide Perovskite Quantum Dots

“…This is also evidenced by a deconvolution analysis of the C 1s XPS spectra (Figure S6) showing inhibited contribution from C−O and C�O. 41 Finally, it should be noted that both OT and MPTMS thiol passivation cause a PL blue shift with the magnitude in proportion to the thiol ligand concentration in the precursor, and the largest blue shift of ∼3 nm is achieved when Φ PL is optimized to near unity (Figure S10). Moreover, the maxima of the PL blue shift seem to be independent of the thiol type, indicating the dominant role of the thiol head group affecting the emission properties.…”

“…Although the 1/e lifetimes are significantly longer than previous results, possibly due to the lower excitation density, the time constants as shown in Figure S11 are more than doubled after thiol ligand exchange, which is comparable to the previous work. All of these results imply that MPTMS-treated PQDs are robust to washing and produce a static QD-ligand interface owing to the cross-link reaction between MPTMS ligands, which also contributes to lower surface polarity and higher moisture/oxygen resistance …”

“…The increase in XPS binding energies of Cs 3d, Pb 4f, and Br 3d (Figure ) indicate higher adsorption energies of the ligands as well as a higher density of Pb–S bonding on the QD-ligand interface, which may cause shifts in the energy level of surface states with reference to band edges, a higher oxidation state, and accordingly less tendency for oxidation in the ambient. This is also evidenced by a deconvolution analysis of the C 1s XPS spectra (Figure S6) showing inhibited contribution from C–O and CO . Finally, it should be noted that both OT and MPTMS thiol passivation cause a PL blue shift with the magnitude in proportion to the thiol ligand concentration in the precursor, and the largest blue shift of ∼3 nm is achieved when Φ PL is optimized to near unity (Figure S10).…”

“…All of these results imply that MPTMS-treated PQDs are robust to washing and produce a static QD-ligand interface owing to the cross-link reaction between MPTMS ligands, which also contributes to lower surface polarity and higher moisture/ oxygen resistance. 41 Lastly, for electroluminescence applications, a vital issue is the poor carrier mobility of QD films, which has been ascribed to the excessive long-alkyl-chain ligands of oleic acid and oleylamine. As shown in Figure 6, the electron and hole transport behavior of the ExMP-CsPbBr 3 QD film, as estimated with electron-only and hole-only devices (EOD and HOD), is comparable to that of ExOT-CsPbBr 3 ; both are one order of magnitude higher than that of the pristine CsPbBr 3 QD film.…”

Boosting the Synthetic Yield and Stability of CsPbBr3 Nanocrystals via Solvent Injection Quenching for Future Microscale Displays

“…Colloidal nanocrystals (NCs) are the rising star in electronic and optoelectronic materials. , These nanoscale semiconductor crystals exhibit outstanding spectral purity, good monodispersity, wide excitation range, and high photoluminescence yield, , which make them promising candidates for light-emitting diodes (LEDs), , photovoltaic devices and photodetectors, microscale color convertor, and flat panel display devices, etc. ,− Additionally, NCs prepared by the solution process are convenient for forming films and can be designed in a variety of sizes and shapes. , These NCs are suitable for high-definition microdisplay applications due to their nanoscale size. Recently, Chen et al synthesized the CsPbX 3 @SiO 2 AG composite film, which exhibited a strong luminous emission intensity .…”