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Quantum dots - Coggle Diagram
Quantum dots
semiconductor
properties dependedent on size and shape of crystal
quantum confinement
size of semiconductor reduced to extent that charged particles is severely constrained in space
size reduced to Bohr excitation radius
average distance between electron and hole in material
QD confines motion of conduction band electrons and valence bands holes
energy bands become discrete
zero degrees of freedom
conduction electrons confined in all spatial directions
Bandgap is inversely proportional to size of QD
Energy (colour) is determined by bandgap energy
Larger QD, lesser energy (redder colour)
Smaller QD, more energy (Bluer colour)
solar cells
convert light energy to electrical energy
photovoltaic effect
when light is shone on semiconductor material, electrons within crystal is freed
only photons with energy matching the semiconductor's bandgap energy can free electrons to produce electric current
Larger energy than band gap
expand extra energy as heat when freeing electrons
Smaller energy than bandgap
pass through material
solar cell efficiency
ratio of electrical output of a solar cell, to incident energy, in the form of sunlight
ECE(%)
η = (Pm /( E ∙ Ac )) × 100%
reflectivity of surface
semiconductor material should have low refractive index
lower reflectivity
solution: antireflective coating
quantum dot solar cell
variety of different energy level can extract more power from solar spectrum
able to absorb light from wide range of solar spectrum
solar cell would be able to deliver power at greater efficiencies
fuel cell
convert hydrogen to electrons
does not cause pollution
Conversion of fuel to energy takes place via an electrochemical process, not combustion.
High efficiency and reliability, multi-fuel capability, durability, scalability and ease of maintenance.
Solar-powered hydrogen-producing fuel cell using electrodes coated with quantum dots
Due to the tunable properties, a larger portion of the solar spectrum can be converted into useful energy
With quantum dots, due to their small size, multiple excited electrons may be produced from absorption of a single high-energy photon, thereby increasing its efficiency
Catalysts are used with fuels such as hydrogen or methanol to produce hydrogen ions
Nanoparticles of platinum can be used to reduce amount of bulk platinum needed
using nanoparticles of other materials to replace platinum entirely and thereby lowering costs
QLED
Able to produce better quality colours than conventional LED
Possible due to size-dependent tuning of photoemission wavelength
Different sized QDs can be used to convert light to nearly any colour in visible spectrum
