We demonstrate that semiconductor nanorods can be used to fabricate readily processed and efficient hybrid solar cells together with polymers. By controlling nanorod length, we can change the distance on which electrons are transported directly through the thin film device. Tuning the band gap by altering the nanorod radius enabled us to optimize the overlap between the absorption spectrum of the cell and the solar emission spectrum. A photovoltaic device consisting of 7-nanometer by 60-nanometer CdSe nanorods and the conjugated polymer poly-3(hexylthiophene) was assembled from solution with an external quantum efficiency of over 54% and a monochromatic power conversion efficiency of 6.9% under 0.1 milliwatt per square centimeter illumination at 515 nanometers. Under Air Mass (A.M.) 1.5 Global solar conditions, we obtained a power conversion efficiency of 1.7%.

We have shown recently that the use of high aspect ratio inorganic nanorods in conjunction with conjugated polymers is a route to obtaining efficient solar cells processed from solution. Here, we demonstrate that the use of binary solvent mixtures in which one of the components is a ligand for the nanocrystals is effective in controlling the dispersion of nanocrystals in a polymer.By varying the concentration of the solvent mixture, phase separation between the nanocrystal and polymer could be tuned from a micron scale down to nanometer scale. In addition, we can achieve nanocrystal surfaces that are free of surfactant through the use of weak binding ligands, which can be removed through heating. Combined, the control of film morphology together with surfactant removal result in nanorod-polymer blend photovoltaic cells with high external quantum efficiency of 59% under 0.1 mW/cm 2 illumination at 450 nm.

water; iv) drying in a nitrogen flow; and v) plasma treatment (Harrick Plasma cleaner/sterilizer PDC-32G) for 2 min. This cleaning procedure results in hydrophilic substrates with a water±air contact angle of less than 10 .The surface modification proceeds as follows: i) adsorption of QNHEC with an average molar mass of 360 kg mol ±1 (AKZO-Nobel Arnhem) from solution (100 mg l ±1 , 0.1 M NaCl, pH 10) onto the silicon wafer for 30 min; ii) rinsing with demineralized water; iii) adsorption of negatively charged uniform spheres of silica of different sizes (LUDOX grades HS-40, SM-30, and TM-50, Aldrich Chemical Company, Inc.; the numbers indicate the silica weight percent in the original purchased colloidal dispersions) from a dilute suspension (100 mg l ±1 , 0.05 M NaCl, pH 7); and iv) rinsing successively with demineralized water and acetone. Finally, the samples are sintered at 1000 C for 5±10 min. In this way the polymer is burnt away, and we end up with a pure silica surface with the same chemical structure as the smooth silicon substrate, which has a native oxide layer. After the cleaning procedure the new surface is again found to be hydrophilic (y H 2 O < 10).The adsorption of QNHEC on silica has recently been studied by Hoogendam et al. [16], from whose results we have chosen our experimental parameters such that we can expect a sufficient adsorption of the polymer on the substrate. Similarly, the conditions for the silica adsorption were taken from publications by Böhmer [13] and Böhmer et al. [14]. By rinsing with water and acetone, respectively, we tried to prevent surface salt deposition and silica particle aggregation as much as possible.Surface and Film Characterization: Ellipsometry (Sentech ellipsometer model SE400, with a rotating analyzer) was used to determine the thickness of the QNHEC film. The topography of this film was imaged using a Nanoscope III AFM (Digital Instruments, Santa Barbara, California). Both contact mode (CM; silicon nitride cantilevers with a spring constant of about 0.58 N/m) and tapping mode atomic force microscropy (TM-AFM; silicon cantilevers with a resonance frequency of about 350±380 kHz) were used. AFM was also used to study the topography and surface roughness of the (sintered) silica particle layer. LCP films were prepared by spin-coating from 1,2-dichloroethane. The repeating unit of the LCP used, as well as its phase behavior, is given in Figure 1. The synthesis and characterization of the phase behavior has been described by Nieuwhof et al. [17].The topography was also measured by AFM. However, for rough surfaces it is impossible to measure the LCP film thickness accurately by ellipsometry. Therefore, test films of the LCP were spin-coated also onto smooth silicon wafers to determine the film thickness. The phase behavior and stability of the LCP films were investigated by optical microscopy (Olympus BX60 equipped with a hot stage and crossed polarizers).

Charge transport in composites of inorganic nanorods and a conjugated polymer is investigated using a photovoltaic device structure. We show that t he current-voltage (I-V) curves in the dark can be modelled using the Shockley equation modified to include series and shunt resistance at low current levels, and using an improved model that incorporates both the Shockley equation and the presence of a space charge limited region at high currents. Under illumination the efficiency of photocurrent generation is found to be dependent on applied bias.Furthermore, the photocurrent-light intensity dependence was found to be sublinear. An analysis of the shunt resistance as a function of light intensity suggests that the photocurrent as well as the fill factor is diminished as a result of increased photoconductivity of the active layer at high light intensity. By studying the intensity dependence of the open circuit voltage for nanocrystals with different diameters and thus band gaps, it was inferred that Fermi-level pinning occurs at the interface between the aluminum electrode and the nanocrystal.3

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Synthetic and X-ray structural details, optical and vibrational spectroscopic, and thermal properties of the materials [(CH 3 ) 4 N] 2 M 2 Ge 4 S 10 (where M ) Cu, Ag), are described for the first time. Rietveld PXRD full-profile structure refinements of [(CH 3 ) 4 N] 2 M 2 Ge 4 S 10 reveal a novel open-framework architecture in which dimetal M 2 2+ and adamantanoid Ge 4 S 10 4building blocks are alternately substituted into the tetrahedral Zn 2+ and S 2sites of a zinc blende lattice, all linked together by [Ge(µ-S)] 2 M-M[(µ-S)Ge] 2 metal-metal bonded bridging units. The metal-metal distances in the S 2 M-MS 2 "twisted I" dihedral unit are 2.761 Å (Ag) and 2.409 Å (Cu). These internuclear separations are shorter than the bulk metals themselves (2.89 Å, Ag; 2.54 Å, Cu). This implies that the adamantanoid Ge 4 S 10 4--based open-framework structure is held together by d 10 -d 10 M + -M + metal-metal bonds. FT-Raman provides a direct probe of this interaction. Dimetal-framework breathing vibrational modes are observed around 38 cm -1 for M ) Ag and 55 cm -1 for M ) Cu. In situ VT-PXRD analysis demonstrates that [(CH 3 ) 4 N] 2 Ag 2 Ge 4 S 10 retains its structural integrity upon exposure to air after in vacuo heating above the [(CH 3 ) 4 N] + loss temperature. It seems likely that the disilver connection of adamantanoid Ge 4 S 10 4building blocks confers thermal stability upon the framework.

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