Size-dependent band gap of colloidal quantum dots

Abstract

The size-dependent band gap of semiconductor quantum dots is a well-known and widely studied quantum confinement effect. In order to understand the size-dependent band gap, different theoretical approaches have been adopted, including the effective-mass approximation with infinite or finite confinement potentials, the tight-binding method, the linear combination of atomic orbitals method, and the empirical pseudopotential method. In the present work we calculate the size-dependent band gap of colloidal quantum dots using a recently developed method that predicts accurately the eigenstates and eigenenergies of nanostructures by utilizing the adiabatic theorem of quantum mechanics. We have studied various semiconductor (CdS, CdSe, CdTe, PbSe, InP, and InAs) quantum dots in different matrices. The theoretical predictions are, in most cases, in good agreement with the corresponding experimental data. In addition, our results indicate that the height of the finite-depth well confining potential is independent of the specific semiconductor of the quantum dot and exclusively depends on the matrix energy-band gap by a simple linear relation.

Tunable mechanical and thermal properties of ZnS/CdS core/shell nanowires

“…The most important characteristic of these nanostructures is very high surface to volume ratio. As a result, surface effects which are negligible in the bulk material, can lead to a significant changes in the mechanical [1,2], thermal [3,4], electronic [5][6][7] and structural [8][9][10][11][12] properties of the nanostructures which are very different from their bulk counterparts. The properties of the nanoparticles can be tuned by functionalizing the nanoparticle by other organic/inorganic materials.…”

Advancing colloidal quantum dot photovoltaic technology

“…This potential cascade design induces an additional built-in electric field and serves as a driving force, which improves the minority carrier transport in device demonstrations. Longer wavelength photons were absorbed closer to the junction, which increased the FF of a graded solar cell [39]. A subsequent study demonstrated efficient exciton transfer mechanisms in EDT-and 1,3-BDT-treated funnels, resulting in enhanced carrier transport and photocurrent [226].…”

“…Though the true costs of scaling up CQD solar cell manufacturing to the gigawatt power scale are unknown, they are expected to be similar to those for organic photovoltaics [36] because of the similarities in materials, synthesis, and growth processes involved in the two technologies. Second, the steady rise in device efficiencies may indicate that CQD films combine the benefits of bulk semiconductors with those of solution-processed molecular materials [37][38][39]. Third, CQDs possess unique optical and electrical properties that could potentially be harnessed in strategies for overcoming the single junction ShockleyQueisser efficiency limit [40].…”

WEAK QUANTUM CONFINEMENT IN ZnO NANORODS: A ONE DIMENSIONAL POTENTIAL WELL APPROACH

“…This band gap depends on the size of the nanocrystals. 21 Hence, we want to find the energy levels by solving the Schrodinger's equation for the electron-hole system in the semiconductor. For this calculation, the terms that should be considered in the Hamiltonian of the systems are (i) kinetic energy of the electron and holes, (ii) the confinement potential and (iii) the Coulombic interaction between electron and hole.…”