An efficient antireflection coating (ARC) can enhance solar cell performance through increased light coupling. Here, we investigate solution-grown ZnO nanostructures as ARCs for Si solar cells and compare them to conventional single layer ARCs. We find that nanoscale morphology, controlled through synthetic chemistry, has a great effect on the macroscopic ARC performance. Compared with a silicon nitride (SiN) single layer ARC, ZnO nanorod arrays display a broadband reflection suppression from 400 to 1200 nm. For a tapered nanorod array with average tip diameter of 10 nm, we achieve a weighted global reflectance of 6.6%, which is superior to an optimized SiN single layer ARC. Calculations using rigorous coupled wave analysis suggest that the tapered nanorod arrays behave like modified single layer ARCs, where the tapering leads to impedance matching between Si and air through a gradual reduction of the effective refractive index away from the surface, resulting in low reflection particularly at longer wavelengths and eliminating interference fringes through roughening of the air-ZnO interface. According to the calculations, we may further improve ARC performance by tailoring the thickness of the bottom fused ZnO layer and through better control of tip tapering.

Room temperature X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICPMS), high resolution Rutherford backscattering spectrometry (HR-RBS), Kelvin probe method, and scanning tunneling microscopy (STM) are employed to study the properties of a freshly exfoliated surface of geological MoS2 crystals. Our findings reveal that the semiconductor 2H-MoS2 exhibits both n- and p-type behavior, and the work function as measured by the Kelvin probe is found to vary from 4.4 to 5.3 eV. The presence of impurities in parts-per-million (ppm) and a surface defect density of up to 8% of the total area could explain the variation of the Fermi level position. High resolution RBS data also show a large variation in the MoSx composition (1.8 < x < 2.05) at the surface. Thus, the variation in the conductivity, the work function, and stoichiometry across small areas of MoS2 will have to be controlled during crystal growth in order to provide high quality uniform materials for future device fabrication.

We introduce a novel approach, nanotransfer printing (nTP), to fabricate top-contact electrodes in Au/1,8-octanedithiol/GaAs junctions. Current− voltage and photoresponse experiments were conducted to evaluate the nature of electrical contact. Results show that the nTP method produces superior devices in which the electrical transport in nTP devices occurs through the 1,8-octanedithiol molecules. By contrast, conventional evaporation of Au onto the molecules results in direct Au/GaAs contacts. Thus, nTP is potentially useful for making electrical contacts in molecular electronics.

Nanostructured films and coatings with controlled surface area, porosity, crystalline orientation, grain sizes, and crystal morphologies are desirable for many applications, including microelectronic devices, chemical and biological sensing and diagnosis, energy conversion and storage (photovoltaic cells, batteries and capacitors, and hydrogen-storage devices), lightemitting displays, catalysis, drug delivery, separation, and optical storage. Meeting the demands of these potential applications, however, will require reliable and economic processes for the production of a large supply of high-quality nanomaterials. Gas-phase reactions [1] have been extensively used to prepare oriented nanostructures including carbon nanotubes, [2,3] ZnO nanowires, [4,5] and many other oxide and non-oxide semiconductor materials, [6,7] but these methods typically require high temperatures (∼ 500-1100°C) and vacuum conditions, which limit the choice of substrate and the economic viability of high-volume production. These limitations have stimulated research on solution-phase synthesis (sometimes referred to as the soft solution route or chemical bath deposition), which offers the potential for low-cost, industrial-scale manufacturing. Low-temperature (typically < 100°C), aqueous-phase approaches are particularly attractive because of their low energy requirements, and safe and environmentally benign processing conditions.In aqueous-phase synthesis, oriented nanocrystalline films are deposited on a substrate in aqueous media by heterogeneous nucleation and subsequent growth. The resultant film structure is controlled by a complicated set of coupled processes in both the solution and solid phases. Heterogeneous nuclea- 335Nanostructured films with controlled architectures are desirable for many applications in optics, electronics, biology, medicine, and energy/chemical conversions. Low-temperature, aqueous chemical routes have been widely investigated for the synthesis of continuous films, and arrays of oriented nanorods and nanotubes. More recently, aqueous-phase routes have been used to produce films composed of more complex crystal structures. In this paper, we discuss recent progress in the synthesis of complex nanostructures through sequential nucleation and growth processes. We first review the use of multistage, seeded-growth methods to synthesize a wide range of nanostructures, including oriented nanowires, nanotubes, and nanoneedles, as well as laminated films, columns, and multilayer heterostructures. We then describe more recent work on the application of sequential nucleation and growth to the systematic assembly of large arrays of hierarchical, complex, oriented, and ordered crystal architectures. The multistage aqueous chemical route is shown to be applicable to several technologically important materials, and therefore may play a key role in advancing complex nanomaterials into applications.-[*] Dr.

Effective infiltration of the polymer into the nanostructured oxide is critical for optimizing the performance of hybrid π-conjugated polymer/nanostructured metal oxide semiconductor photovoltaic devices. We investigated the effect of polymer processing parameters, solvent selection, and thermal annealing on poly(3-hexylthiophene) (P3HT)/ZnO nanorod photovoltaic devices and found that these play an important role in the degree of polymer infiltration and the subsequent device performance. We demonstrate that using dichlorobenzene as a solvent produced better performance devices than using chloroform. In addition, the infiltration of P3HT into the ZnO nanorod array has been improved through annealing and subsequent slow cooling. Time-resolved microwave conductivity studies reveal an increase in the photoconductivity of the composite devices with annealing, resulting from changes in both the polymer and ZnO. The device performance was shown to increase with enhanced infiltration, and the devices that had been slow cooled from melt at 225 °C demonstrated a V OC of 440 mV, a J SC of 1.33 mA/cm2, a fill factor of 48%, and a power conversion efficiency of 0.28%. In contrast to previously published results on P3HT infiltrated into mesoporous TiO2 (Appl. Phys. Lett. 2003, 83, 3380), we found that the device performance improves with increasing amount of the polymer embedded in the ZnO arrays, through proper solvent selection and polymer processing.