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Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy.

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Simple and efficient methods of organizing materials are key to the realization of a nanotech world. These authors report on recent developments in simple evaporation‐induced self‐assembly processes, which enable the rapid production of patterned porous or nanocomposite materials. The Figure shows a calcined particle exhibiting vesicular mesophase, which was generated by aerosol self‐assembly of the tri‐block copolymer P123.

Nanocomposite materials are widespread in biological systems. Perhaps the most studied is the nacre of abalone shell, an orientated coating composed of alternating layers of aragonite (CaCO 3 ) and a biopolymer. Its laminated structure simultaneously provides strength, hardness and toughness: containing about 1 vol. % polymer, nacre is twice as hard and 1,000 times as tough as its constituent phases 1 . Such remarkable properties have inspired chemists and materials scientists to develop synthetic, 'biomimetic' nanocomposite assemblies 2-5 . Nonetheless, the efficient processing of layered organic-inorganic composites remains an elusive goal. Here we report a rapid, efficient selfassembly process for preparing nanolaminated coatings that mimic the structure of nacre. Beginning with a solution of silica, surfactant and organic monomers, we rely on evaporation during dip-coating to induce the formation of micelles and partitioning of the organic constituents into the micellar interiors 6 . Subsequent self-assembly of the silica-surfactant-monomer micellar species into lyotropic mesophases 7 simultaneously organizes the organic and inorganic precursors into the desired nanolaminated form. Polymerization fixes this structure, completing the nanocomposite assembly process. This approach may be generalized both to other composite architectures and to other materials combinations.Natural nanocomposites are formed by biomineralization 5 , a templated self-assembly process in which pre-organized organic surfaces regulate the nucleation, growth, morphology and orientation of inorganic crystals. Related synthetic, so-called 'biomimetic', approaches include crystallization beneath Langmuir monolayers 8 , crystallization on self-assembled monolayers 3,9 , supramolecular self-assembly 2,6,10 and sequential deposition 11 . Of these, only the last two offer the ability to introduce periodic microstructural and compositional changes needed for nanocomposite assembly. With regard to nanolaminated structures, supramolecular self-assembly has resulted in the formation of lamellar (silica/surfactant) films 12 or letters to nature 256

Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells and light emitting diodes. Here we show that band edge positions of lead sulfide (PbS) colloidal semiconductor nanocrystals, specifically quantum dots (QDs), can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control through the development of simple, robust and scalable solution-phase ligand exchange methods, which completely replace native ligands with functionalized cinnamate ligands, allowing for well-defined, highly tunable chemical systems. By combining experiments and ab initio simulations, we establish clear relationships between QD surface chemistry and the band edge positions of ligand/QD hybrid systems. We find that in addition to ligand dipole, inter-QD ligand shell inter-digitization contributes to the band edge shifts. We expect that our established relationships and principles can help guide future optimization of functional organic/inorganic hybrid nanostructures for diverse optoelectronic applications.

Nature abounds with intricate composite architectures composed of hard and soft materials synergistically intertwined to provide both useful functionality and mechanical integrity. Recent synthetic efforts to mimic such natural designs have focused on nanocomposites, prepared mainly by slow procedures like monomer or polymer infiltration of inorganic nanostructures or sequential deposition. Here we report the self-assembly of conjugated polymer/silica nanocomposite films with hexagonal, cubic or lamellar mesoscopic order using polymerizable amphiphilic diacetylene molecules as both structure-directing agents and monomers. The self-assembly procedure is rapid and incorporates the organic monomers uniformly within a highly ordered, inorganic environment. Polymerization results in polydiacetylene/silica nanocomposites that are optically transparent and mechanically robust. Compared to ordered diacetylene-containing films prepared as Langmuir monolayers or by Langmuir-Blodgett deposition, the nanostructured inorganic host alters the diacetylene polymerization behaviour, and the resulting nanocomposite exhibits unusual chromatic changes in response to thermal, mechanical and chemical stimuli. The inorganic framework serves to protect, stabilize, and orient the polymer, and to mediate its function. The nanocomposite architecture also provides sufficient mechanical integrity to enable integration into devices and microsystems.

We present the synthesis and device characterization of new hole transport materials (HTMs) for application in solid-state dye-sensitized solar cells (ssDSSCs). In addition to possessing electrical properties well suited for ssDSSCs, these new HTMs have low glass transition temperatures, low melting points, and high solubility, which make them promising candidates for increased pore filling into mesoporous titania films. Using standard device fabrication methods and Z907 as the sensitizing dye, power conversion efficiencies (PCE) of 2.94% in 2-μm-thick cells were achieved, rivaling the PCE obtained by control devices using the state-of-the-art HTM spiro-OMeTAD. In 6-μm-thick cells, the device performance is shown to be higher than that obtained using spiro-OMeTAD, making these new HTMs promising for preparing high-efficiency ssDSSCs.