Spatial dimensionality affects the degree of confinement when an electron-hole pair is squeezed from one or more dimensions approaching the bulk exciton Bohr radius (a(B)) limit. The electron-hole interaction in zero-dimensional (0D) dots, one-dimensional (1D) rods/wires, and two-dimensional (2D) wells/sheets should be enhanced by the increase in confinement dimensions in the order 0D > 1D > 2D. We report the controlled synthesis of PbS nanomaterials with 0D, 1D, and 2D forms retaining at least one dimension in the strongly confined regime far below a(B) (approximately 10 nm for PbS) and provide evidence through varying the exciton-phonon coupling strength that the degree of confinement is systematically weakened by the loss of confinement dimension. Geometry variations show distinguishable far-field optical polarizations, which could find useful applications in polarization-sensitive devices.

Monocomponent quantum dots (QDs) possess limited electron−hole delocalization capacity upon photoexcitation that suppresses the efficiency of photoenergy harvesting devices. Type II heterostructures offer band offsets at conduction and valence bands depending upon the band gaps of the constituent QDs which largely depend on their sizes. Hence, by keeping the size of one constituent QD fixed while varying the size of the other QD selectively, the band offsets at the interface can be engineered selectively. We report on the tuning of band offsets by synthesizing component size modulated heterostructures composed of a fixed sized ZnSe QD and size tuned CdS QDs with variable band gaps. The resultant heterostructures show spontaneous charge carrier separation across the interface upon photoexcitation depending on the extent of band offsets. Formation mechanism, epitaxial relationship, and the intrinsic nature of interface of the heterostructures are investigated. Experimental results are corroborated with ab initio electronic structure calculations based on density functional theory. Spontaneous charge carrier delocalization across the interface depends on the magnitude of band offsets, which facilitates fabrication of QD sensitized solar cells (QDSSCs). Improved device performances of QDSSCs in comparison to the limited photon-to-current conversion efficiencies of monocomponent QDs demonstrates the significance of band offsets for natural charge carrier separation.

Coupled quantum semiconductor dots are often referred to as artifi cial molecules because their electronic properties are dictated by the mutual interaction of two constituent blocks. [ 1 , 2 ] Unlike the electronic property tuning by varying the size or shape of a single nanomaterial, coupled quantum dots rely on controlling energy states via band-offset engineering at the material interface. [ 3 , 4 ] The possibility of obtaining long-range optical tunability from coupled quantum dots demonstrates a route for going far beyond the limits imposed by individual nanomaterials by the spatial separation of the charge carriers, which provides yet another important way to tailor nanomaterial properties. Coupled semiconductor heterostructures are typically classifi ed as type-I or type-II depending on the relative alignment of the conduction and valence bands of the constituent materials forming the heterointerface. [5][6][7] For a type-II coupled structure, the relative alignment of the conduction and valence bands of the constituent materials offers a spatially indirect bandgap resulting in a transition energy gap smaller than the bandgaps of either of the constituting semiconductors. Thus, such coupled structures offer engineering of the energy gap by variation of component sizes or extent of diffusion at the interface. Recent interest in component-modulated coupled materials include core/shell nanostructures, heterojunctions, and superlattices, which offer diverse functionalities due to the spatial charge distribution across the material junctions. [ 8 -13 ] Synthesis of facet selective multicomponent heterostructures, such as hetero-nanorods, [14][15][16][17] tetrapods, [ 18 ] and dumbbells have drawn signifi cant scientifi c importance because of their capability for exciton separation within a single coupled material. [ 19 , 20 ] However, these structures often lead to a disappearance of emission owing to the spatially separated nanoradiative intermediate states and lack in-plane conformation variation capability due to one and multidimensional morphologies. [ 21 ] The promise of in-plane conformation variation is of practical importance because a fi xed biasing across a close-packed monolayer of asymmetric coupled dots may provide a route to control electronic properties for different conformations that may lead in realizing the q-bits for quantum information processing, [ 22 , 23 ] in addition to application in optoelectronic devices. [24][25][26] In principle, control over coupled junction provides a means for controlling quantum coupling interactions, the extent of which can be controlled by tuning synthetic conditions. The intermixing between constituent nanomaterials may result in new intermediate transition states depending on the size of the constituents, which could be useful in tailoring long-range emissions in the visible or IR range. Here, we report a simple route for tailoring emission over the entire visible range by chemically designing type-II asymmetric coupled quantum dots composed of di...