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We demonstrate additive shelling of PbS core quantum dots by CdS using room-temperature colloidal atomic layer deposition. Combining in-depth electron microscopy, absorption spectroscopy and elemental analysis, we present a structural model of the PbS/CdS core/shell quantum dots after each of the successive colloidal ALD cycles. In particular, we find that such core/shell quantum dots are cation-rich and we argue that this nonstoichiometry should be attributed to a Cd-excess at the outer surface. Analyzing various PbS/CdS core/shell QDs, we demonstrate that CdS shells have no effect on the energy of the PbS band-edge transition for PbS core QDs larger than ≈4 nm, a finding we support by effective mass calculations. In spite of this, CdS shell growth generally decreases the photoluminescence quantum yield of PbS/CdS core/shell QDs as compared to PbS core QDs. This suggests that photoluminescence quenching is mainly caused by defects at the PbS/CdS interface. [ABSTRACT FROM AUTHOR]

Cadmium selenide quantum dots (QDs) have been dispersed in a discotic liquid crystal columnar matrix. Thermophysical properties of these liquid crystal nanocomposites were investigated by UV-Vis spectroscopy, photoluminescence spectroscopy, differential scanning calorimetry, polarizing optical microscopy, DC conductivity and small angle X-ray diffraction. [ABSTRACT FROM AUTHOR]

The all‐inorganic nature of CsPbI3 perovskites allows to enhance stability in perovskite devices. Research efforts have led to improved stability of the black phase in CsPbI3 films; however, these strategies—including strain and doping—are based on organic‐ligand‐capped perovskites, which prevent perovskites from forming the close‐packed quantum dot (QD) solids necessary to achieve high charge and thermal transport. We developed an inorganic ligand exchange that leads to CsPbI3 QD films with superior phase stability and increased thermal transport. The atomic‐ligand‐exchanged QD films, once mechanically coupled, exhibit improved phase stability, and we link this to distributing strain across the film. Operando measurements of the temperature of the LEDs indicate that KI‐exchanged QD films exhibit increased thermal transport compared to controls that rely on organic ligands. The LEDs exhibit a maximum EQE of 23 % with an electroluminescence emission centered at 640 nm (FWHM: ≈31 nm). These red LEDs provide an operating half‐lifetime of 10 h (luminance of 200 cd m−2) and an operating stability that is 6× higher than that of control devices. [ABSTRACT FROM AUTHOR]

The all‐inorganic nature of CsPbI3 perovskites allows to enhance stability in perovskite devices. Research efforts have led to improved stability of the black phase in CsPbI3 films; however, these strategies—including strain and doping—are based on organic‐ligand‐capped perovskites, which prevent perovskites from forming the close‐packed quantum dot (QD) solids necessary to achieve high charge and thermal transport. We developed an inorganic ligand exchange that leads to CsPbI3 QD films with superior phase stability and increased thermal transport. The atomic‐ligand‐exchanged QD films, once mechanically coupled, exhibit improved phase stability, and we link this to distributing strain across the film. Operando measurements of the temperature of the LEDs indicate that KI‐exchanged QD films exhibit increased thermal transport compared to controls that rely on organic ligands. The LEDs exhibit a maximum EQE of 23 % with an electroluminescence emission centered at 640 nm (FWHM: ≈31 nm). These red LEDs provide an operating half‐lifetime of 10 h (luminance of 200 cd m−2) and an operating stability that is 6× higher than that of control devices. [ABSTRACT FROM AUTHOR]

The all‐inorganic nature of CsPbI3 perovskites allows to enhance stability in perovskite devices. Research efforts have led to improved stability of the black phase in CsPbI3 films; however, these strategies—including strain and doping—are based on organic‐ligand‐capped perovskites, which prevent perovskites from forming the close‐packed quantum dot (QD) solids necessary to achieve high charge and thermal transport. We developed an inorganic ligand exchange that leads to CsPbI3 QD films with superior phase stability and increased thermal transport. The atomic‐ligand‐exchanged QD films, once mechanically coupled, exhibit improved phase stability, and we link this to distributing strain across the film. Operando measurements of the temperature of the LEDs indicate that KI‐exchanged QD films exhibit increased thermal transport compared to controls that rely on organic ligands. The LEDs exhibit a maximum EQE of 23 % with an electroluminescence emission centered at 640 nm (FWHM: ≈31 nm). These red LEDs provide an operating half‐lifetime of 10 h (luminance of 200 cd m−2) and an operating stability that is 6× higher than that of control devices. [ABSTRACT FROM AUTHOR]

Perovskite‐based light‐emitting diodes (PeLEDs) are now approaching the upper limits of external quantum efficiency (EQE); however, their application is currently limited by reliance on lead and by inadequate color purity. The Rec. 2020 requires Commission Internationale de l'Eclairage coordinates of (0.708, 0.292) for red emitters, but present‐day perovskite devices only achieve (0.71, 0.28). Here, lead‐free PeLEDs are reported with color coordinates of (0.706, 0.294)—the highest purity reported among red PeLEDs. The variation of the emission spectrum is also evaluated as a function of temperature and applied potential, finding that emission redshifts by <3 nm under low temperature and by <0.3 nm V−1 with operating voltage. The prominent oxidation pathway of Sn is identified and this is suppressed with the aid of H3PO2. This strategy prevents the oxidation of the constituent precursors, through both its moderate reducing properties and through its forming complexes with the perovskite that increase the energetic barrier toward Sn oxidation. The H3PO2 additionally seeds crystal growth during film formation, improving film quality. PeLEDs are reported with an EQE of 0.3% and a brightness of 70 cd m−2; this is the record among reported red‐emitting, lead‐free PeLEDs. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have gained attention for their optoelectronic properties and are employed as the active layer in solar cells, light‐emitting diodes, and photodetectors. However, the use of lead in the best‐performing perovskite devices may limit their wider application. Prior reports of lead‐free perovskite nanoparticles have exhibited linewidths more than twice as wide as their lead‐halide counterparts, limiting their attainable color gamut. Here the solution synthesis of lead‐free Rb3Sb2I9 nanoplatelets and single crystals is reported; the single crystals exhibit broad (full‐width at half‐maximum (FWHM) = 75 nm) photoluminescence centered at 635 nm, while the nanoplatelets exhibit narrow emission (FWHM = 21 nm) at 512 nm. The photoluminescence quantum yield of both the single crystals and nanoplatelets is low and the present demonstration of the narrowest emission among all lead‐free perovskites reported to date motivates further study of how these and related materials can achieve further‐enhanced brightness. [ABSTRACT FROM AUTHOR]