Semiconductor nanoparticle with high level of circularity and electroluminescent device including same
An electroluminescent device includes a first electrode; a second electrode spaced apart from the first electrode; and a light emitting layer disposed between the first electrode and the second electrode, the light emitting layer includes semiconductor nanoparticles, wherein the semiconductor nanoparticles do not include cadmium, the semiconductor nanoparticles have a core shell structure, the semiconductor nanoparticles include zinc, selenium, tellurium, and sulfur, wherein in a two dimensional image obtained by an electron microscopy analysis, the semiconductor nanoparticles show an average value of a circularity defined by the following equation of greater than or equal to about 0.8 and less than or equal to about 1: circularity = 4 π × Area [ Perimeter ] 2 wherein Area is an area of a two dimensional image of an individual semiconductor nanoparticle, and Perimeter is a circumference of the two dimensional image of the individual semiconductor nanoparticle.
1 . An electroluminescent device comprising
a first electrode;
a second electrode spaced apart from the first electrode; and
a light emitting layer disposed between the first electrode and the second electrode,
wherein the light emitting layer comprises semiconductor nanoparticles, wherein the semiconductor nanoparticles do not comprise cadmium,
wherein the semiconductor nanoparticles have a core shell structure and comprise zinc, selenium, tellurium, and sulfur,
wherein in a two dimensional image obtained by an electron microscopy analysis, an average circularity of the semiconductor nanoparticles is greater than 0.8 and less than or equal to about 1, a circularity being defined by the following formula:
circularity
=
4
π
×
Area
[
Perimeter
]
2
wherein Area is an area of a two dimensional image of an individual semiconductor nanoparticle, and Perimeter is a circumference of the two dimensional image of the individual semiconductor nanoparticle.
2 . The electroluminescent device of claim 1 , wherein the electroluminescent device further comprises a hole auxiliary layer between the light emitting layer and the first electrode,
wherein the electroluminescent device further comprises an electron auxiliary layer between the light emitting layer and the second electrode, or a combination thereof, and optionally wherein the hole auxiliary layer comprises an organic compound, the electron auxiliary layer comprises zinc magnesium metal oxide nanoparticles, or a combination thereof.
3 . The electroluminescent device of claim 1 , wherein an average size of the semiconductor nanoparticles is greater than or equal to about 5 nanometers and less than or equal to about 50 nanometers.
4 . The electroluminescent device of claim 1 , wherein the core shell structure comprises a core comprising a first semiconductor nanocrystal and a semiconductor nanocrystal shell disposed on the core,
wherein the first semiconductor nanocrystal comprises a first zinc chalcogenide comprising zinc, selenium, and tellurium, and
wherein the semiconductor nanocrystal shell comprises a second zinc chalcogenide comprising zinc and sulfur and optionally a third zinc chalcogenide comprising zinc and selenium.
5 . The electroluminescent device of claim 4 , wherein as determined by a transmissive electron microscopy analysis of the semiconductor nanoparticles, a thickness variance of the semiconductor nanocrystal shell determined by the following equation is less than or equal to about 0.3:
thickness variance=( T max −T min )/( T max )
wherein
T max is a maximum thickness of the semiconductor nanocrystal shell in a given semiconductor nanoparticle, and
T min is a minimum thickness of the semiconductor nanocrystal shell in a given semiconductor nanoparticle.
6 . The electroluminescent device of claim 1 , wherein in the semiconductor nanoparticles, a mole ratio of tellurium to selenium is greater than 0:1 and less than or equal to about 0.1:1;
or
wherein in the semiconductor nanoparticles, a mole ratio of a sum of sulfur and selenium to zinc is greater than or equal to about 0.88:1 and less than or equal to about 3:1.
7 . The electroluminescent device of claim 1 , wherein the average circularity of the semiconductor nanoparticles is greater than 0.81.
8 . The electroluminescent device of claim 1 , wherein the semiconductor nanoparticles do not comprise an indium phosphide, a gallium phosphide, manganese, copper, or a combination thereof.
9 . The electroluminescent device of claim 1 , wherein the light emitting layer is configured to emit light with a quantum yield or quantum efficiency of greater than 75% when irradiated with light, and the light emitting layer has a quantum yield maintenance value of greater than or equal to about 80%, after a 30 minute heat treatment at about 80° C.
10 . The electroluminescent device of claim 1 , wherein the light emitting layer is configured to emit blue light having a maximum luminescent peak wavelength of greater than or equal to about 400 nanometers and less than or equal to about 500 nanometers when a voltage is applied between the first electrode and the second electrode,
and wherein the electroluminescent device has a maximum external quantum efficiency of greater than or equal to about 7.5% and less than or equal to about 40%, a maximum luminance of greater than or equal to about 10,000 candelas per square meter and less than or equal to about 200,000 candelas per square meter, or a combination thereof.
11 . Semiconductor nanoparticles, wherein the semiconductor nanoparticles comprise zinc, selenium, tellurium, and sulfur and do not comprise cadmium,
wherein the semiconductor nanoparticles are configured to emit blue light,
wherein in a two dimensional image obtained by an electron microscopy analysis, the semiconductor nanoparticles show an average value of a circularity defined by the following equation of greater than 0.8 and less than or equal to about 1:
circularity
=
4
π
×
Area
[
Perimeter
]
2
wherein Area is an area of a two dimensional image of an individual semiconductor nanoparticle, and Perimeter is a circumference of the two dimensional image of the individual semiconductor nanoparticle.
12 . The semiconductor nanoparticles of claim 11 , wherein an average particle size of the semiconductor nanoparticles is greater than or equal to about 9 nanometers and less than or equal to about 12 nanometers and a standard deviation of sizes of the semiconductor nanoparticles is greater than or equal to about 3% and less than or equal to about 15% of the average particle size; or
wherein the semiconductor nanoparticles do not comprise an indium phosphide, a gallium phosphide, manganese, copper, or a combination thereof.
13 . The semiconductor nanoparticles of claim 11 , wherein the semiconductor nanoparticles comprise a core comprising a first semiconductor nanocrystal and a semiconductor nanocrystal shell disposed on the core,
wherein the first semiconductor nanocrystal comprises a first zinc chalcogenide comprising zinc, selenium, and tellurium, and
wherein the semiconductor nanocrystal shell comprises a second zinc chalcogenide comprising zinc and sulfur and optionally a third zinc chalcogenide comprising zinc and selenium.
14 . The semiconductor nanoparticles of claim 13 , wherein as determined by a transmissive electron microscopy analysis of the semiconductor nanoparticles, a thickness variance of the semiconductor nanocrystal shell determined by the following equation is less than or equal to about 0.3:
thickness variance=( T max −T min )/( T max )
wherein
T max is a maximum thickness of the semiconductor nanocrystal shell in a given semiconductor nanoparticle, and
T min is a minimum thickness of the semiconductor nanocrystal shell in a given semiconductor nanoparticle.
15 . The semiconductor nanoparticles of claim 11 , wherein the semiconductor nanoparticles comprise a mole ratio of tellurium to selenium of greater than 0:1 and less than or equal to about 0.1:1 or a mole ratio of a sum of selenium and sulfur to zinc of greater than or equal to about 0.88:1 and less than or equal to about 3:1.
16 . The semiconductor nanoparticles of claim 11 , wherein the average circularity of the semiconductor nanoparticles is greater than 0.81.
17 . A method of producing the semiconductor nanoparticles of claim 11 , which comprises:
conducting a reaction between a zinc precursor and a sulfur precursor in the presence of a particle comprising a first semiconductor nanocrystal comprising zinc, selenium, and tellurium to form a semiconductor nanocrystal shell comprising zinc and sulfur to produce the semiconductor particles,
wherein in the reaction, a mole ratio of the sulfur precursor to the zinc precursor is greater than or equal to about 2.4:1.
18 . A display device comprising the semiconductor nanoparticles of claim 11 .
19 . The display device of claim 18 , wherein the display device comprises a handheld terminal, a monitor, a notebook computer, a television, an electronic display board, a camera, or a part of an autonomous vehicle.
20 . Semiconductor nanoparticles comprising:
a core comprising a first semiconductor nanocrystal comprising a first zinc chalcogenide comprising zinc, selenium, and tellurium; and
a shell disposed on the core, the shell comprising a second semiconductor nanocrystal comprising a second zinc chalcogenide comprising zinc and sulfur and optionally a third zinc chalcogenide comprising zinc and selenium,
wherein the semiconductor nanoparticles are configured to emit blue light having a maximum luminescent peak wavelength of greater than or equal to about 430 nanometers and less than or equal to about 480 nanometers, and
as determined by a transmissive electron microscopy analysis of the semiconductor nanoparticles, a thickness variance of the semiconductor nanocrystal shell determined by the following equation is less than or equal to about 0.3:
thickness variance=( T max −T min )/( T max )
wherein
T max is a maximum thickness of the semiconductor nanocrystal shell in a given semiconductor nanoparticle, and
T min is a minimum thickness of the semiconductor nanocrystal shell in a given semiconductor nanoparticle.