We show by numerical simulations that discretized versions of commonly studied continuum nonlinear growth equations (such as the Kardar-Parisi-Zhang equation and the Lai-Das Sarma equation) and related atomistic models of epitaxial growth have a generic instability in which isolated pillars (or grooves) on an otherwise flat interface grow in time when their height (or depth) exceeds a critical value. Depending on the details of the model, the instability found in the discretized version may or may not be present in the truly continuum growth equation, indicating that the behavior of discretized nonlinear growth equations may be very different from that of their continuum counterparts. This instability can be controlled either by the introduction of higher-order nonlinear terms with appropriate coefficients or by restricting the growth of pillars (or grooves) by other means. A number of such "controlled instability" models are studied by simulation. For appropriate choice of the parameters used for controlling the instability, these models exhibit intermittent behavior, characterized by multiexponent scaling of height fluctuations, over the time interval during which the instability is active. The behavior found in this regime is very similar to the "turbulent" behavior observed in recent simulations of several one-and two-dimensional atomistic models of epitaxial growth. 61.50.Cj, 68.55.Bd, 05.70.Ln, 64.60.Ht

Graphene quantum dots (GQDs) synthesized by a direct chemical method have been used in combination with ZnO nanowires (NWs) to demonstrate their potential as a solar harvesting material in photovoltaic cells exhibiting an open circuit voltage of 0.8 V. The excited state interaction between the photoexcited GQDs and the ZnO NWs has been verified from the charge-transfer process by both emission spectroscopy and photovoltaic measurements. This work has implications for less expensive and efficient next generation solid-state solar cells.

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Synthesis of various nanostructured semiconductor materials and processing them for different device fabrications has been at the forefront of research for the last two decades. In comparison to spherical nanoparticles, anisotropic materials e.g. nanorods, nanowires, and nanodisks have been widely explored to obtain a better performance of the devices. In addition, it is also well-known that nanomaterials, on doping with suitable impurities, can enhance the device sensitivity and speed. Combining both, we report here the synthesis of micrometer long In2S3 nanosheets and on doping them with Cu(I), we have studied here their photoresponse properties. These nanosheets are synthesized in a high temperature colloidal method following a catalytic thermal decomposition of a single source precursor of In and S. From various TEM, HRTEM, and HAADF images the growth pattern of these sheets is investigated, and the obtained moiré fringes at the overlapped region are discussed. Finally, the comparative study of the device performance has been carried out with introducing different amounts of copper in these nanosheets.

We report on an efficient hybrid Si nanocrystal quantum dot modified radial p-n junction thinner Si solar cell that utilizes the advantages of effective exciton collection by energy transfer from nanocrystal-Si (nc-Si) quantum dots to underlying radial p-n junction Si nanowire arrays with excellent carrier separation and propagation via the built-in electric fields of radial p-n junctions. Minimization of recombination, optical, and spectrum losses in this hybrid structure led to a high cell efficiency of 12.9%.

p - Zn O ∕ n - Si heterojunction is achieved by depositing Al–N codoped p-type ZnO film on n-Si by low-cost sol-gel technique. The junction shows good diode characteristics with rectification ratio (IF∕IR)∼10 at 4V in the dark. The photoresponse of the heterojunction is investigated by studying the current-voltage characteristics under the ultraviolet (370nm) and visible light (450nm) illuminations. By fitting the experimental data, we have proposed the current transport mechanism to be dominated by the recombination tunneling at lower and by the space-charge limited current at higher forward voltages, which are further supported by the photocapacitance and photocurrent spectra.

Inorganic/organic hybrid radial heterojunction solar cells that combine vertically-aligned n-type silicon nanowires (SiNWs) with poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) have great potential for replacing commercial Si solar cells. The chief advantage of such solar cells is that they exhibit higher absorbance for a given thickness than commercial Si solar cells, due to incident light-trapping within the NW arrays, thus enabling lower-cost solar cell production. We report herein on the effects of NW length, annealing and surface electrode on the device performance of SiNW/PEDOT:PSS hybrid radial heterojunction solar cells. The power conversion efficiency (PCE) of the obtained SiNW/PEDOT:PSS hybrid solar cells can be optimized by tuning the thickness of the surface electrode, and the etching conditions during NW formation and post-annealing. The PCE of 9.3% is obtained by forming efficient transport pathways for photogenerated charge carriers to electrodes. Our approach is a significant contribution to design of high-performance and low-cost inorganic/organic hybrid heterojunction solar cells.

The authors report on the self-seeded growth of ZnO nanowire (NW) arrays on glass substrates by a simple solvothermal method using two different sol concentrations for the seed layer formation. The formations of hexagonal-shaped NWs with diameter of 20–60nm on the seed layer for 0.1M sol and mostly of trapezoidal-shaped NWs with base width of 135nm on the seed layer for 0.03M sol have been explained considering the longitudinal and transversal growths of ZnO NWs. The photocurrent behavior of ZnO NW arrays in air as well as in vacuum is analyzed in terms of adsorbed oxygen and water molecules.