The quantum dots (QDs) are colloidal semiconductor nanocrystals whose optical and electronic properties are governed by the quantum confinement effect. When the physical dimension of the nanocrystal becomes smaller than the exciton Bohr radius, continuous energy bands split into discrete, atomic-like electronic states, allowing the effective bandgap to be precisely tuned via particle size.

Because of their nanoscale dimensions, QDs exhibit a remarkably high surface-to-volume ratio, leaving a high density of under-coordinated surface atoms that can act as deep trap states and non-radiative recombination centers. To mitigate high surface energy, prevent irreversible aggregation, and passivate these electronic trap sites, QDs are synthesized with a shell of organic capping ligands (such as long-chain fatty acids or amines).

Beyond ensuring colloidal stability and determining solubility in polar or non-polar solvents, these ligand molecules dictate the interdot distance within assembled thin films. This spacing acts as an insulating tunneling barrier that critically influences charge carrier mobility, interparticle electronic coupling, and overall optoelectronic performance in devices like light-emitting diodes and photodetectors.