1. Title (28 point)
QD 광학기술
강 성 준
경희대학교
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Introduction
Quantum-dots Light emitting diodes
Photodetectors
JCP 130, 094704 (2009)
Fabrication of high-performance Quantum-dots LEDs
Interfacial electronic structures of LEDs
Highly transparent photodetector (NIR/RGB/UV)
Device fabrications
Optical logic circuits
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Introduction
https://lant.khu.ac.kr/home
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Outline
- Quantum Mechanics and Optics for QDs
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Introduction: Anything else?
Any other functions on Display?
Participants can vote at slido.com with #1398420
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Introduction: Anything else?
2022년 수강생들의 생각
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Introduction: Anything else?
2023년 수강생들의 생각
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Introduction: Research trend in electronics
Notebook
Smart Phone
Smart Glass
& Watch
Desktop
Research trend in electronics
Attachable
Electronics
Rigid Electronics
Portable
Apple, Samsung, HP, etc.
Weight: less than 2 kg
Power: Battery
Rigid & Flexible
Portable
Apple, Samsung, Google, etc.
Weight: ~ 200 g
Power: Battery
Rigid & Flexible
Transparent
Portable
Google, Samsung, Apple, etc.
Weight: ~ 40 g
Power: Battery
Rigid Electronics
Not portable
HP, Sony, Samsung, etc.
Weight: over 5 kg
Power: No battery
Flexible & Stretchable
Transparent
Attachable
Weight: less than 10g
Power: Self generating
New-type of electronics is flexible & stretchable electronics
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Introduction: Research trend in Display
Next?
Solution processable
Flexible, Stretchable, Soft
Pure Color, Printable process
New-type LED, 3D-LED
Quantum-dots LEDs may be the next generation display
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Introduction: future of display?
Display with multi-functions
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Introduction: future of display?
Display with multi-functions
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Introduction: Transparent electronics
Transparent electronics
Electronic devices on transparent substrate, such as a glass and plastic.
Electronic devices with a transparent conducting, semiconducting and insulating materials.
We need small band gap semiconductors for the electrical properties.
Also, we need wide band gap semiconductors for the transparency.
(Sometimes, it can be achieved by using atomically thin semiconductor layers)
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Introduction: Flexible & Stretchable electronics
Flexible electronics
Electronic devices on flexible plastic substrates.
Flexible electronics are lightweight, bendable, rollable, and portable.
Stretchable electronics
Electronics devices on elastic substrates.
Acceptable for foldable, wearable and bio-integrated devices.
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Introduction: Research trend in electronics
Why stretchable?
It allows for applications that are able to deform according to the human body.
It allows for devices that are made in one size and are accommodated to their final shape.
It allows 3D, randomly shaped objects produced in a conventional way.
It improves the reliability of devices subjected to strains.
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Outline
- Quantum Mechanics and Optics for QDs
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Quantum Dots
Quantum dots are small nano crystals, that are considered as dimensionless.
Quantized energy level due to the quantum confinement effect.
Quantum
dots
Narrow
spectral emission bandwidth
Good photo stability
Controllable band gap
(size tuning)
Unlimited on
any substrates & structures
High photoluminescence quantum efficiency
Printed electronics available
High brightness
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Quantum-dots Light Emitting Diodes
Quantum dot LEDs are characterized by pure and saturated emission colors with narrow bandwidth.
QLEDs’ emission wavelength is easily tuned by changing the size of the quantum dots.
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Quantum Dots: Core-shell structures
Type-Ⅱ QDs can be used as an energy-conversion material in solar cells.
E(eV)
Anode
HIL
EIL
Cathode
EML
P3HT:PC71BM
hν
h
e-
h
e-
h
e-
E(eV)
Anode
HIL
EIL
Cathode
EML
HTL
ETL
e-
h
h
e-
h
e-
h
e-
hν
Type-Ⅰ QDs can be used to photoluminescence (PL) and electroluminescence (EL) devices
For the light emitting device
For the light absorbing device
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Quantum Dots: Core-shell structures
Types of quantum-dots structure for optoelectronics
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Full color quantum dot display by SAMSUNG (PL emitter)
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Full color quantum dot display by SAMSUNG (EL-emitter)
Using a soft lithography method, they fabricated QLEDs.
Nature Photonics 5, 176 (2011)
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Outline
- Quantum Mechanics and Optics for QDs
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Introduction to Quantum Mechanics
In order to understand the current-voltage characteristics, we need some knowledge of electron behavior in semiconductor when the electron is subjected to various potential functions.
Classic Mechanics
Newton’s law
- Describe macro world.
Quantum Mechanics
Wave Mechanics
- Describe atomic world.
- Schrodinger’s wave equation.
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Introduction to Quantum Mechanics
Classical Mechanics vs. Quantum Mechanics
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Principles of Quantum Mechanics; wave-particle duality
In our experiences, particles and waves are always different concepts.
- Stone is a particle and sound is a wave.
Therefore, particles and waves are treated as a separate
components in classical physics.
In the microscopic world, it is difficult to separate the concepts of particles and waves. That means the wave-particle duality.
We regard electrons as particles because they have charge and mass and behave according to the laws of particle mechanics.
However, sometimes moving electrons can be explained by wave.
Electromagnetic waves are waves because it shows diffraction, interference and polarization.
However, sometimes electromagnetic waves behave as though they are streams of particles.
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Principles of Quantum Mechanics; Photoelectric effect
The energies of electrons liberated by light depend on the frequency of the incident light.
Electrons are emitted when the frequency of the incident light is sufficiently high. The phenomena is known as the photoelectric effect and the emitted electron are called photoelectrons.
From the photoelectric effect, we know that light waves carry energy.
However, it is very difficult to explain the photoelectric effect by using classical physics.
Einstein explained the photoelectric effect and won the Nobel prize.
(He didn’t get the Nobel prize by the theory of relativity.)
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Principles of Quantum Mechanics; Photoelectric effect
In 1905, Einstein realized that the photoelectric effect could be understood if the energy in light is not spread out over wavefronts but is concentrated in small packets PHOTONS.
Photon, with a light of frequency ν, has the energy hν, which is same with the Planck’s quantum energy.
From the concept of photons, Einstein enables to explain three experimental findings, which is difficult to explain the photoelectric effect by using wave theory (or classical physics).
1. Because of EM wave energy is concentrated in photons, there should be no delay in the emission of photoelectrons.
2. All photons of frequency ν have the same energy. So changing the intensity of monochromatic light beam will change the number of photoelectrons but not their energies.
3. The higher the frequency ν, the greater the photon energy hν. Therefore the photoelectrons have more energy with the higher frequency.
Therefore, we can guess that light is packets of energy.
PHOTON
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Principles of Quantum Mechanics; De Broglie waves
A moving body behaves as it has a wave nature.
A photon of light of frequency ν has the momentum.
Therefore the wavelength of a photon is specified by its momentum according to the relation below. De Broglie suggest the equation could be applied to the materials with mass as well as a photon.
The momentum of a particle of mass m and velocity v is p=γmv. Therefore, we can define De Broglie wavelength.
γ is the relativistic factor. If the speed of mass m is very small compare to the speed of light, the relativistic factor should be 1.
De Broglie wavelength shows that the particles with a larger momentum has the shorter De Broglie wavelength.
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Principles of Quantum Mechanics; Wave formula
The wave formula can be changed as below.
ϖ is defined as angular frequency and k is wave number.
Therefore, the wave formula can be written as below.
Using these equation we will learn the phase velocity and group velocity of waves.
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Principles of Quantum Mechanics; Phase and group velocities
A group of waves do not need to have the same velocity as the waves themselves.
Phase velocity is the velocity of waves itself.
Group velocity is the velocity of wave packet or wave group.
The wave group can be formed by superposition of the waves.
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Principles of Quantum Mechanics; Phase and group velocities
The amplitude of the de Broglie waves that correspond to a moving body reflects the probability that it will be found at a particular place at a particular time.
We can not use the simple harmonic wave formula to describe de Broglie waves, because the amplitude of simple harmonic wave is same everywhere.
Therefore, we can expect a moving body can be represented by a wave packet (wave group).
Using the wave group, the probability is different at a particular place and a particular time because the amplitude is different with x, t.
Amplitude is same everywhere. Amplitude is different with the position or time.
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Principles of Quantum Mechanics; Particle in a box
Let’s try to understand why the energy of trapped particle is quantized.
When a particle is restricted to a specific region of space instead of free space,
the wave nature of a moving particle shows some remarkable phenomena.
Let’s consider the simplest case such as the figure. (a particle bounces back and forth between the walls of a box.)
And if we assume the walls of the box are infinitely hard, so the particle does not lose energy by the collision. And the velocity is sufficiently small, so that we can ignore relativistic considerations.
In this case, a particle trapped in a box is like a standing wave such as the image.
The wave’s displacement should be 0 at the wall, since the wave stop there.
Therefore, the possible de Broglie wavelengths of the particle in a box are
determined by the width L of the box.
The longest wavelength is λ=2L, the next is λ=L and then λ=2L/3 and so forth.
Therefore, de Broglie wavelengths of trapped particle is given by
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Principles of Quantum Mechanics; Particle in a box
The restriction on de Broglie wavelength gives the limits on momentum of the particle and also on the kinetic energy. (mv=h/λ)
The kinetic energy is shown below.
The particle in a box does not have a potential energy in this model. Therefore the total energy of the particle in a box is given as below.
From this equations, we can find that the energy is not continuous. Each permitted energy is called as an energy level. The integer n is called as quantum number.
Therefore the energy of the particle in a box is quantized.
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Principles of Quantum Mechanics; Particle in a box
From the equation, we can find some general conclusions.
electron shell
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Principles of Quantum Mechanics; The Bohr atom
Bohr and de Broglie found a successful atomic model.
The de Broglie wavelength of electron in orbit around a hydrogen nucleus and the velocity of electron for a stable orbit are given as below.
By combining these equations, we can obtain the orbital electron wavelength as a function of r, the radius of the electron orbit.
The radius of the electron orbit of hydrogen is 5.3 × 10-11 m. Therefore, the electron wavelength can be calculated as below.
The electron wavelength is exactly same with the circumference of the
electron orbit.
The orbit of the electron corresponds to one complete electron wave.
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Principles of Quantum Mechanics; The Bohr atom
The wavelengths of the electron wave should be always fit an integer number of times of the circumference of the electron orbit.
If a fractional number of wavelengths is not same to the circumference of the electron orbit, destructive interference will occur as the waves travel around the loop, and the vibrations will disappear.
Therefore, an electron can circle a nucleus only if its orbit contains an integral number of de Broglie wavelengths.
This statement combines both the particle and wave characters of the electron because the electron wavelength depends on the orbital velocity needed to balance the pull of the nucleus.
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Principles of Quantum Mechanics; The Bohr atom
The condition for orbit stability can be written as below.
rn is the radius of the orbit that contain n wavelengths. The integer n is called as the quantum number of the orbit.
Therefore, the orbital radii in Bohr atom is
The radius of the innermost orbit is called as the Bohr radius of the hydrogen atom.
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Electron Orbits
Let’s try to obtain the electron velocity in classical mechanics, which can make a stable electron orbit.
In hydrogen atom, there are only one electron as shown in the image.
If we assume a circular electron orbit, the centripetal force and the electric force between proton and electron is given by as below.
These force should be same for a stable orbit.
Therefore the electron velocity for a stable orbit is obtained as below.
Under this velocity, electron should collapse to the proton.
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Electron Orbits
Let’s try to obtain the total energy of the electron in a hydrogen atom.
The total energy should be the sum of kinetic energy and potential energy.
Here, the minus sign of potential energy follows from the choice of PE = 0 at r = ∞, when the electron and proton are infinitely far apart so that there is no potential energy.
The total energy of the electron in a hydrogen atom is
If the total energy is larger than 0, the electron should be separate from the proton.
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Principles of Quantum Mechanics; Energy levels and spectra
The various permitted orbits according to the Bohr’s atomic model related with the different electron energies.
The electron energy En is given in terms of the orbit
radius rn.
By combination those two equations, we can obtain
the energy level formula.
Here, the lowest energy level E1 is called the ground
state of the atom, and the higher levels E2, E3, E4, …
are called excited states.
As the quantum number n increases, the energy level
approaches to 0. And the electron is no longer bound
to the nucleus.
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The failure of classical physics
The analysis for a stable electron orbit based on classical dynamic are shown below.
We obtained these equation from Newton’s law and Coulomb’s law.
However, scientist didn’t consider the electromagnetic theory, which states that any accelerated electric charges radiate energy in the form of electromagnetic waves.
And an electron, who is moving in the curve or circle, is accelerated.
Therefore, the electron in the orbit should always lose energy continuously, and spiraling into the nucleus in a short time as shown in the image. (Atom should be collapse in this model.)
But, the atoms do not collapse.
Therefore there are contradiction in the orbit model.
We need a new model to describe the atomic structure based on Quantum Physics!!
✔
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Principles of Quantum Mechanics; Quantum Mechanics
The quantities, that quantum mechanics describe, are probabilities.
For example, the radius of the electron’s orbit in a ground state hydrogen
is 5.3 × 10-11 m.
However quantum mechanics states that this is the most probable radius.
That means in the experiment, most trial will give a different value, either larger
or smaller, but the value most likely to be found at 5.3 × 10-11 m.
From the De Broglie electron wave, we can say the electron can be exist at some place with some probability.
✔
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Principles of Quantum Mechanics; Quantum Mechanics
WAVE FUNCTION
The quantity with which quantum mechanics is concerned is the wave function Ψ of a body.
While Ψ itself has no physical interpretation, the square of its absolute magnitude⎟Ψ⎥2, evaluated at a particular place and time, is proportional to the probability of finding the body there at that time.
The quantum mechanics is about to determine Ψ for a body when its freedom of motion is limited by the external forces.
The wave functions are usually complex with both real and imaginary parts.
However, a probability must be a positive real quantity. The probability density ⎟Ψ⎥2 for a complex Ψ is taken as the product Ψ* Ψ. Ψ* is called as complex conjugate of Ψ.
Therefore, ⎟Ψ⎥2 is always a positive real quantity.
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Principles of Quantum Mechanics; Quantum Mechanics
Normalization
Because ⎟Ψ⎥2 is proportional to the probability density P of finding the body described by Ψ, the integral of ⎟Ψ⎥2 over all space must be finite. That means the body should be somewhere.
If the integration of ⎟Ψ⎥2 is 0, the particle does not exist.
⎟Ψ⎥2 is the probability, therefore the integration should be 1 to have a meaning.
A wave function that obeys this relation is said to be normalized.
Every acceptable wave function can be normalized by multiplying it by an appropriate constant.
Besides being normalizable, Ψ must be single-valued, since probability can have only one value at a particular place and time, and continuous.
Also the partial derivatives of Ψ should be finite, continuous, and single valued.
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Principles of Quantum Mechanics; The wave equation
Schrödinger’s equation is a wave equation in the variable Ψ.
Schrödinger’s equation is the fundamental equation of quantum mechanics in the same sense that the second law of motion (F=ma) is the fundamental equation of classical mechanics.
Let’s consider the wave equation below.
The wave equation describes a wave whose variable quantity is y that propagates in the x direction with the speed v.
Waves in the xy plane traveling in the x direction along a stretched string lying on the x axis.
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Principles of Quantum Mechanics; The wave equation
Therefore, the wave equation above has the solution in the form as below, where F is any function that can be differentiated.
The solution F(t - x/v) represent waves traveling in the +x direction, and the solution F(t + x/v) represent waves traveling in the –x direction.
Let’s consider the wave of a free particle. The wave can be described by the general solution of the wave equation for a constant amplitude A, constant angular frequency ω in the +x direction as below.
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Schrödinger’s equation: Time-dependent form
The wave function Ψ for a particle moving freely in the +x direction is specified as below.
By replacing ω in the formula by 2πν and v by λν,
Also, by using the relation between total energy E and momentum p with the λ and ν, we can obtain the wave function for a free particle in terms of Energy and Momentum.
The equation describes the wave of a free particle of total energy E and momentum p moving in the +x direction.
To obtain the fundamental differential equation of Ψ, which we can solve for Ψ in a specific situation, we have to use differential formula.
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Schrödinger’s equation: Time-dependent form
By differentiating two times with respect to x,
By differentiating once with respect to t,
The total energy is given as below, and we can obtain the time dependent form of Schrödinger’s equation.
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Schrödinger’s equation: Time-dependent form
The time dependent form of Schrödinger’s equation in three dimensions are shown.
Any restrictions that may be present on the particle’s motion will affect the potential energy U.
Therefore, once we know U, by solving the Schrödinger’s equation , we can obtain the wave function Ψ and the probability density ⎟Ψ⎥2 in terms of x, y, z, t.
Schrödinger’s equation is a basic principle of physics itself.
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The infinite potential well
Let’s see the eigenvalue and eigenfunction of a particle in a box.
We can specify the particle’s motion by restricting the motion along x-axis
between x = 0 and x = a with infinitely hard walls.
A particle does not lose energy when it collides with such walls. So the
total energy stays constant.
The potential is constant inside the wall. (let’s assume 0).
Therefore, the wave function is 0 outside the box.
Therefore, the Schrödinger’s equation within the box can be written as below.
The wave function ψ is a function only of x, so we can use total derivative instead partial derivative form.
The solution of the Schrödinger’s equation is below.
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The infinite potential well
The boundary condition is
The constant A1 should be 0 because, ψ = 0 for x = 0.
For ψ = 0 for x = a, it should be satisfy the condition below.
Therefore, from this relation, we can obtain the eigenvalues of energy levels.
The result shows the permitted energy of a particle in a box.
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The infinite potential well
From the boundary condition we know that the constant A1 should be 0 because, ψ = 0 for x = 0.
And, also with normalization,
This eigenfunctions are corresponded to the energy eigenvalues En.
This result means that the energy of the particle is quantized.
e-
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Quantum dots; Energy levels
Therefore, quantum dots are more closely related to atoms than a bulk materials because of their maximized quantized energy levels.
We can also called as “Artificial atoms”.
Band gaps and energy levels of quantum dots depend on the size of crystals.
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Introduction to the Quantum Theory of Solids
Now, we will generalize the concepts to the electron in a crystal lattice.
e-
e-
e-
e-
e-
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The k-space diagram
The parameter 𝛼 is related to the total energy E of the particle.
🡺 Energy band & Energy gap exist in crystal !!!!
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Quantum dot
Quantum dots are small nano crystals, that are considered as dimensionless.
Typical dimensions are in several nanometers.
Quantum dots are small nano crystals, that contain a tiny droplet of free electrons.
A quantum dot is a semiconductor nano crystal whose electrons are confined in three spatial dimensions.
The size, shape and number of electrons can be controlled.
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Quantum dots; Energy levels and spectra
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Electromagnetic frequency spectrum
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Quantum Dots
Quantum dots are small nano crystals, that are considered as dimensionless.
Quantized energy level due to the quantum confinement effect.
Quantum
dots
Narrow
spectral emission bandwidth
Good photo stability
Controllable band gap
(size tuning)
Unlimited on
any substrates & structures
High photoluminescence quantum efficiency
Printed electronics available
High brightness
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Quantum Dots: Core-shell structures
Types of quantum-dots structure for optoelectronics
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Quantum Dots: Core-shell structures
Type-Ⅱ QDs can be used as an energy-conversion material in solar cells.
E(eV)
Anode
HIL
EIL
Cathode
EML
P3HT:PC71BM
hν
h
e-
h
e-
h
e-
E(eV)
Anode
HIL
EIL
Cathode
EML
HTL
ETL
e-
h
h
e-
h
e-
h
e-
hν
Type-Ⅰ QDs can be used to photoluminescence (PL) and electroluminescence (EL) devices
For the light emitting device
For the light absorbing device
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Outline
- Quantum Mechanics and Optics for QDs
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Quantum Dots TV?
Samsung
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Research challenges in QLEDs
Materials
Quantum-dots
- High efficient, stable.
- Ligand control.
- Cadmium free.
Interface engineering
Interfacial electronic structure
- XPS/UPS measurements.
- Charge injection/transport interlayer.
Fabrications
Developing fabrication processes
- Transfer printing, Jet printing, etc.
- Vacuum jet coating.
- Compatible process with OLEDs.
Nature Communications 6, 7149 (2015)
Nano Letters 15, 969 (2015)
Charge injection/transport layer
- Efficient charge injection/transport.
- Air and thermal stable.
- Inorganic.
Interfacial enhancement
- Plasmon resonance.
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IDEA: improving the performance of QLEDs
Interfacial and plasmon effects
New charge transport layer
Engineering interfacial energy band for efficient charge transport and recombination
Plasmon effect to enhance the luminance
- Au nanorod, etc.
Replace organic charge injection and transport layer for stability
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Quantum-dot LEDs: plasmon effect
Au NRs Coating
on the patterned ITO
PEDOT:PSS coating
TFB coating
QD coating
TiO2 coating
Al deposition
Plasmon enhanced QLEDs with Au nanorods.
- A strong coupling between excitons and localized surface plasmons.
QDs
Al
TiO2
ITO
Glass
100 nm
10 nm
25 nm
60 nm
Au NRs
PEDOT:PSS & TFB
QDs
E(eV)
ITO
PEDOT:PSS
TIO2
Al
4.8
5.1
4.9
6.9
3.9
4.3
5.3
2.1
TFB
Au NRs
7.8
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Quantum-dot LEDs: plasmon effect
glass
Au NR
ITO
PEDOT:PSS
TFB
QDs
TiO2
Al
2. Plasmon resonance-
induced emission
1. General emission
Ec
Ev
+
-
+
-
-
+
CdSe/ZnS QD
Excitation
1. General emission
2. Plasmon resonance-
induced emission
Plasmon enhanced QLEDs with Au nanorods.
- Nonradiative excitons can make an energy transfer to plasmon effectively.
- A strong coupling between excitons and localized surface plasmons generates a plasmon resonance.
- The resonance can be scattered and make radiation from Au nanorods.
Plasmon resonance induced emission from Au nanorods.
Time-resolved PL measurements
It will provide an evidence of plasmon enhanced QLEDs.
100nm
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Quantum-dot LEDs: inorganic charge injection layer
Solution-processed Tungsten Oxide and Zinc Oxide
ACS Appl. Mater. Interfaces 6, 495 (2014)
Solution-processed Nickel Oxide and Zinc Oxide
Nanotechnology 24, 115201 (2013)
Solution-processed Molybdenum Oxide
IEEE Photonics Tech. Lett. 28, 2156 (2016)
Metal doped Nickel Oxide
Adv. Funct. Mater. 28, 1704278 (2017)
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Quantum-dot LEDs: inorganic charge injection layer
Remove organic layers such as PEDOT:PSS.
- Improve thermal stability and prevent hygroscopic nature of organics.
Vanadium oxide hole injection layer works well.
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Quantum-dot LEDs: inorganic charge injection layer
Interfacial energy band diagram of vanadium oxide HIL.
- Gap state was found to improve the charge injection.
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Quantum-dot LEDs: inorganic charge injection layer
Interfacial energy band diagram of vanadium oxide HIL.
- Gap state was found to improve the charge injection.
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Quantum-dot LEDs
S&T Market Report
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Quantum-dot LEDs
삼성전자 QLED TV (QDEF)
Nanosys의 양자점 적용 디스플레이)
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Scientific issues: Transparent visible-light photodetectors
Transparent visible-light photodetectors for wearable electronics.
- For the visible-light photodetectors, we need small band-gap semiconductors.
- However, small band-gap materials are not transparent.
- On the other hands, wide band-gap semiconductors are transparent.
- But, wide band-gap semiconductors can absorb only high-energy photon, such as UV.
We need a new approach for the transparent & visible-light photodetectors.
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IDEA: for a highly transparent visible-light photodetector
Transparent RGB photodetector using Quantum dots.
Wide band gap semiconductor + controllable band gap quantum dots
(for the transparent active channel) (for the visible light absorber)
Conventional RGB photodetector
Transparent RGB photodetector
Color filter array
Depth dependent & stacked silicon photodiodes
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Visible-light phototransistors: hybrid film of Ge-doped InGaO & QDs
Applied Physics Letters, 106, 031112 (2015)
The photo responsivity shows a selective response to the 650 nm light source.
External quantum efficiency to the 650 nm light source was 1.25 × 104.
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Visible-light phototransistors: origin of the photocurrent
Applied Physics Letters, 106, 031112 (2015)
From the UPS measurements of oxide semiconductor and quantum-dot films, ionization energy of each materials can be calculated.
From the energy level diagram, the origin of the photocurrent in visible light was small band gap QDs
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Visible-light phototransistors: QDs at the channel region
Possible of efficient charge transport.
Respond to the periodic light . (up to 50 Hz)
SiO2/Si
IGZO
Al
hν
Al
Al
hν �(λ = 635 nm)
e-
e-
e-
QD
IGZO
Photocurrent
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
Al
200 nm
Quantum-Dot
Al
SiO2
Si
IGZO
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Visible-light phototransistors: Solution process
SiO2 (100 nm)
Heavily doped Si
ZnO
Al
Al
SiO2 (100 nm)
Heavily doped Si
ZnO
Al
Al
QDs
Red Laser
(635 nm)
Solution processable device.
- Solution ZnO film instead of sputtered IGZO.
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Visible-light phototransistors: Solution process & color selective response
Si/SiO2
ZnO
Al
Al
Si/SiO2
ZnO
Al
Al
QDs
Si/SiO2
ZnO
Al
Al
QDs
Si/SiO2
ZnO
Al
Al
QDs
RGB quantum-dots on solution ZnO film
- Solution ZnO film instead of sputtered IGZO
- Color selective photocurrent
unpublished
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Visible-light phototransistors: Solution process & color selective response
Stacking RGB quantum-dots on solution ZnO film
- Solution ZnO film instead of sputtered IGZO
- Color selective photocurrent
unpublished
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QDs: future of optoelectronics?
Samsung’s First Look event in New York will showcase new 4K QLED TVs (2018)
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