Here, we present a ligand exchange of long insulating molecules with short, robust, and environmentally friendly iodide ions via a mild flocculation of PbSe nanocrystals (NCs). This ligand exchange leads to the formation of stable colloidal solutions in various polar solvents and in a broad concentration range via electrostatic repulsion. The iodide capping ligands preserve the electronic structure and maintain the optical properties of the PbSe NCs, both in solution and in the form of solid films. The spin-coated PbSe NC solids exhibit good transport characteristics with electron mobilities in the linear and saturation regimes reaching (2.1 ± 0.3) cm 2 /(V•s) and (2.9 ± 0.4) cm 2 /(V•s), respectively. This opens up opportunities for the low-cost and low-temperature fabrication of NC thin films being attractive for applications in the fields of electronics and optoelectronics.

Förster resonance energy transfer (FRET) interacted with localized surface plasmon (LSP) gives us the ability to overcome inadequate transfer of energy between donor and acceptor nanocrystals (NCs). In this paper, we show LSP-enhanced FRET in colloidal photosensors of NCs in operation, resulting in substantially enhanced photosensitivity. The proposed photosensitive device is a layered self-assembled colloidal platform consisting of separated monolayers of the donor and the acceptor colloidal NCs with an intermediate metal nanoparticle (MNP) layer made of gold interspaced by polyelectrolyte layers. Using LBL assembly, we fabricated and comparatively studied seven types of such NC-monolayer devices (containing only donor, only acceptor, Au MNP-donor, Au MNP-acceptor, donor-acceptor bilayer, donor-Au MNP-acceptor trilayer, and acceptor-Au MNP-donor reverse trilayer). In these structures, we revealed the effect of LSP-enhanced FRET and exciton interactions from the donor NCs layer to the acceptor NCs layer. Compared to a single acceptor NC device, we observed a significant extension in operating wavelength range and a substantial photosensitivity enhancement (2.91-fold) around the LSP resonance peak of Au MNPs in the LSP-enhanced FRET trilayer structure. Moreover, we present a theoretical model for the intercoupled donor-Au MNP-acceptor structure subject to the plasmon-mediated nonradiative energy transfer. The obtained numerical results are in excellent agreement with the systematic experimental studies done in our work. The potential to modify the energy transfer through mastering the exciton-plasmon interactions and its implication in devices make them attractive for applications in nanophotonic devices and sensors.

We report a large-area, semi-transparent, light-sensitive nanocrystal skin (LS-NS) platform consisting of single monolayer colloidal nanocrystals. LS-NS devices, which were fabricated over areas up to 48 cm(2) using spray-coating and several cm-squares using dip-coating, are operated on the principle of photogenerated potential buildup, unlike the conventional charge collection. Implementing proof-of-concept devices using CdTe nanocrystals with ligand removal, we observed a substantial sensitivity enhancement factor of ~73%, accompanied with a 3-fold faster response time (<100 ms). With fully sealed nanocrystal monolayers, LS-NS is found to be highly stable under ambient conditions, promising for low-cost large-area UV/visible sensing in windows and facades of smart buildings.

gration atop electronic substrates (e.g., using dip coating, spin coating and drop casting), where lattice mismatch problems do not arise. Therefore, these NCs are promising candidates for applications in diverse areas, such as in light-emitting diodes, [ 3 ] solar cells, [ 4 ] and photodetectors [ 5 ] as well as for biolabeling [ 6 ] and biosensing. [ 7 ] Conventional photodetectors using NCs typically operate on the principle of collecting photogenerated charges, where an external bias must be applied for the charge collection. Although photodetectors comprising a Shockley-Schottky barrier can in principle be operated without an applied bias (in the open circuit mode), this would commonly come at the cost of decreasing the sensitivity. Recent research efforts increasingly focus on NC photodetectors that show a remarkable level of sensitivity [ 8 ] and short response times. [ 9 ] These photodetectors do, however, rely on photocurrent collection and commonly exhibit high dark current, which results in high noise levels and limits the device's detection capabilities. [ 10 ] As an alternative photosensor architecture, NC skins offer the potential of high sensitivity for large-area applications because they operate on the principle of photogenerated voltage buildup in the absence of an external bias. With a single NC layer in the device structure, noise generation is signifi cantly reduced, which enhances the device sensitivity. [

We report enhanced sensitization of silicon through nonradiative energy transfer (NRET) of the excitons in an energy-gradient structure composed of a cascaded bilayer of green- and red-emitting CdTe quantum dots (QDs) on bulk silicon. Here NRET dynamics were systematically investigated comparatively for the cascaded energy-gradient and mono-dispersed QD structures at room temperature. We show experimentally that NRET from the QD layer into silicon is enhanced by 40% in the case of an energy-gradient cascaded structure as compared to the mono-dispersed structures, which is in agreement with the theoretical analysis based on the excited state population-depopulation dynamics of the QDs. © 2013 AIP Publishing LLC