Domain and network aggregation of CdTe quantum rods within Langmuir-Blodgett monolayers

Crafting semiconductor organic-inorganic nanocomposites via placing conjugated polymers in intimate contact with nanocrystals for hybrid solar cells

Semiconductor organic-inorganic hybrid solar cells incorporating conjugated polymers (CPs) and nanocrystals (NCs) offer the potential to deliver efficient energy conversion with low-cost fabrication. The CP-based photovoltaic devices are complimented by an extensive set of advantageous characteristics from CPs and NCs, such as lightweight, flexibility, and solution-processability of CPs, combined with high electron mobility and size-dependent optical properties of NCs. Recent research has witnessed rapid advances in an emerging field of directly tethering CPs on the NC surface to yield an intimately contacted CP-NC nanocomposite possessing a well-defined interface that markedly promotes the dispersion of NCs within the CP matrix, facilitates the photoinduced charge transfer between these two semiconductor components, and provides an effective platform for studying the interfacial charge separation and transport. In this Review, we aim to highlight the recent developments in CP-NC nanocomposite materials, critically examine the viable preparative strategies geared to craft intimate CP-NC nanocomposites and their photovoltaic performance in hybrid solar cells, and finally provide an outlook for future directions of this extraordinarily rich field.

Self-assembly of CdTe tetrapods into network monolayers at the air/water interface

Cadmium telluride (CdTe) tetrapods are synthesized with varying aspect ratios through multiple injections of the Te precursor, which provides an excellent means of controlling and tailoring the optical properties of the tetrapods. The self-assembly of CdTe tetrapods at the air/water interface is explored using the Langmuir-Blodgett (LB) technique due to potential use in solar cells arising from the intriguing tetrapod shape that improves charge transport and the optimum band gap energy of CdTe that enhances light absorption. Interestingly, the Langmuir isotherm shows two pressure plateau regions: one at approximately 10 mN/m with the other at the high surface pressure of approximately 39 mN/m. LB deposition at various pressures allows the discernment of the unique two-dimensional packing alluded in the isotherm. By placing CdTe at the air/water interface, it is revealed in the deposition that the tetrapods experienced a dewetting phenomenon, forming a ribbon structure at the onset of surface pressure with a height corresponding to the length of one tetrapod arm. With the increase of surface pressure, the ribbons widen to an eventual large-scale percolated network pattern. The packing density of tetrapods is successfully manipulated by controlling the surface pressure, which may find promising applications in optoelectronic devices.

Bulk and surface assembly of branched amphiphilic polyhedral oligomer silsesquioxane compounds

This study probes the behavior of two series of organic-functionalized core-shell silsesquioxane (POSS-M)p-(x/y) derivatives with various hydrophobic-hydrophilic terminal group compositions in the bulk state and within mono- and multilayered films at the air-water interface and on solid surface. POSS-M refers to mixed silsesquioxane cores, in contrast to the geometrically specific POSS compounds. It is composed of polyhedra, incompletely condensed polyhedra, ladder-type structures, linear structures, and all the possible combinations thereof and attracts great interest because of its facile preparation, low polydispersity, high yield, and low cost. The two series of (POSS-M)p-(x/y) molecules are different in hydrophobic-hydrophilic balance of their terminal groups, with x and y respectively referring to the molar percent of -OCONH-C(18)H(37) tails and -OH for p = 1 and the percent of -OCONH-C(18)H(37) tails and -OCO-C(6)H(4)COOH terminal groups for p = 2. In the bulk state, the presence of aromatic rings in (POSS-M)2-(x/y) series resulted in a lower symmetry crystal structure than the (POSS-M)1-(x/y) series. Moreover, the (POSS-M)p-(x/y) molecules that contain a sufficient amount of -OCONH-C(18)H(37) tails exhibit double endothermic transition, which attributed to the melting of alkyl chains followed by the melting of the unit cells of (POSS-M) cores. The surface morphologies for the various hydrophobic-hydrophilic combinations at surface pressure p = 0.5 mN/m are similar to that observed for the classical amphiphilic star polymers. However, at higher surface pressure (p > or = 5 mN/m), the POSS-M compounds with lower content of hydrophilic groups form a uniform monolayer.