Mesoporous ceramics and semiconductors enable low-cost solar power, solar fuel, (photo)catalyst and electrical energy storage technologies. State-of-the-art, printable high-surface-area electrodes are fabricated from thermally sintered pre-formed nanocrystals. Mesoporosity provides the desired highly accessible surfaces but many applications also demand long-range electronic connectivity and structural coherence. A mesoporous single-crystal (MSC) semiconductor can meet both criteria. Here we demonstrate a general synthetic method of growing semiconductor MSCs of anatase TiO2 based on seeded nucleation and growth inside a mesoporous template immersed in a dilute reaction solution. We show that both isolated MSCs and ensembles incorporated into films have substantially higher conductivities and electron mobilities than does nanocrystalline TiO2. Conventional nanocrystals, unlike MSCs, require in-film thermal sintering to reinforce electronic contact between particles, thus increasing fabrication cost, limiting the use of flexible substrates and precluding, for instance, multijunction solar cell processing. Using MSC films processed entirely below 150 °C, we have fabricated all-solid-state, low-temperature sensitized solar cells that have 7.3 per cent efficiency, the highest efficiency yet reported. These high-surface-area anatase single crystals will find application in many different technologies, and this generic synthetic strategy extends the possibility of mesoporous single-crystal growth to a range of functional ceramics and semiconductors.

We report the first successful application of an ordered bicontinuous gyroid semiconducting network in a hybrid bulk heterojunction solar cell. The freestanding gyroid network is fabricated by electrochemical deposition into the 10 nm wide voided channels of a self-assembled, selectively degradable block copolymer film. The highly ordered pore structure is ideal for uniform infiltration of an organic hole transporting material, and solid-state dye-sensitized solar cells only 400 nm thick exhibit up to 1.7% power conversion efficiency. This patterning technique can be readily extended to other promising heterojunction systems and is a major step toward realizing the full potential of self-assembly in the next generation of device technologies.

Metal-halide perovskite light-absorbers have risen to the forefront of photovoltaics research offering the potential to combine low-cost fabrication with high power-conversion efficiency. Much of the development has been driven by empirical optimisation strategies to fully exploit the favourable electronic properties of the absorber layer. To build on this progress, a full understanding of the device operation requires a thorough optical analysis of the device stack, providing a platform for maximising the power conversion efficiency through a precise determination of parasitic losses caused by coherence and absorption in the non-photoactive layers. Here we use an optical model based on the transfer-matrix formalism for analysis of perovskite-based planar heterojunction solar cells using experimentally determined complex refractive index data. We compare the modelled properties to experimentally determined data, and obtain good agreement, revealing that the internal quantum efficiency in the solar cells approaches 100%. The modelled and experimental dependence of the photocurrent on incidence angle exhibits only a weak variation, with very low reflectivity losses at all angles, highlighting the potential for useful power generation over a full daylight cycle

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solution processing with interesting optoelectronic properties such as high charge transport mobility. Many of the best performing conjugated polymers, including the poly(alkylthiophene)s, derive their high charge mobility from an ability to crystallize. [ 1 , 2 ] While charge transport along an individual conjugated chain is predicted to be extremely rapid, [ 3 ] over longer distances charge must also pass between chains. [ 4 ] Crystallization aids interchain charge transfer by bringing planarized chains together in regular, more intimate contact. The importance of crystalline morphology has been established by previous studies reporting the sensitivity of measured charge transport to fi lm formation parameters that impose the kinetics of crystallization. [5][6][7] However, systematic study of transport-limiting morphological features and how one might optimize crystalline structure remain extremely challenging because of the diffi culty of incremental control over crystallization. In particular, typical solution casting conditions (even from high boiling point carrier solvents [ 5 ] ) lead to extremely high nucleation density, such that macroscopic charge transport probes average over an enormous number of randomly oriented grain boundaries whose density is neither well-known or easily adjusted. [ 8 , 9 ] Methodologies, such as self seeding, adapted from studies of classical semicrystalline polymers, exist that permit systematic control of important morphological characteristics such as nucleation density and lamellar width. We show how controlled solvent swelling and deswelling of a precast poly(3-hexylthiophene) (P3HT) fi lm is an extremely effective method for controlling crystalline morphology (independent of fi lm formation) by fully incremental control of nucleation density over many orders of magnitude.In P3HT and many other main chain conjugated polymers, crystallization is dominated by strong π − π interactions perpendicular to the thiophene ring, which drive a highly anisotropic growth of stacked aggregates. When confi ned to a thin fi lm, the π -stacking [010] direction lies in-plane, with the molecules adopting an edge-on orientation ([100] alkyl side chains aligned perpendicular to the substrate). Long crystalline lamellae separated by amorphous regions containing chain folds and ends provide effi cient in-plane transport channels along the π -stacking direction. Device transport characteristics, While molecular ordering via crystallization is responsible for many of the impressive optoelectronic properties of thin-fi lm semiconducting polymer devices, crystalline morphology and its crucial infl uence on performance remains poorly controlled and is usually studied as a passive result of the conditions imposed by fi lm deposition parameters. A method for systematic control over crystalline morphology in conjugated polymer thin fi lms by very precise control of nucleation density and crystal growth conditions is presented. A precast poly(3-hexylthiophene) fi lm is fi rst swollen into a solution-lik...

A fundamental understanding of the relationship between the bulk morphology and device performance is required for the further development of bulk heterojunction organic solar cells. Here, non‐optimized (chloroform cast) and nearly optimized (solvent‐annealed o‐dichlorobenzene cast) P3HT:PCBM blend films treated over a range of annealing temperatures are studied via optical and photovoltaic device measurements. Parameters related to the P3HT aggregate morphology in the blend are obtained through a recently established analytical model developed by F. C. Spano for the absorption of weakly interacting H‐aggregates. Thermally induced changes are related to the glass transition range of the blend. In the chloroform prepared devices, the improvement in device efficiency upon annealing within the glass transition range can be attributed to the growth of P3HT aggregates, an overall increase in the percentage of chain crystallinity, and a concurrent increase in the hole mobilities. Films treated above the glass transition range show an increase in efficiency and fill factor not only associated with the change in chain crystallinity, but also with a decrease in the energetic disorder. On the other hand, the properties of the P3HT phase in the solvent‐annealed o‐dichlorobenzene cast blends are almost indistinguishable from those of the corresponding pristine P3HT layer and are only weakly affected by thermal annealing. Apparently, slow drying of the blend allows the P3HT chains to crystallize into large domains with low degrees of intra‐ and interchain disorder. This morphology appears to be most favorable for the efficient generation and extraction of charges.

We integrate mesostructured titania arrays into dye-sensitized solar cells by replicating ordered, oriented one-dimensional (1D) columnar and three-dimensional (3D) bicontinuous gyroid block copolymer phases. The solar cell performance, charge transport, and recombination are investigated. We observe faster charge transport in 1D "wires" than through 3D gyroid arrays. However, owing to their structural instability, the surface area of the wire arrays is low, inhibiting the solar cell performance. The gyroid morphology, on the other hand, outperforms the current state-of-the-art mesoporous nanoparticle films.

The morphology of TiO 2 plays an important role in the operation of solid-state dye-sensitized solar cells. By using polyisoprene-block-ethyleneoxide (PI-b-PEO) copolymers as structure-directing agents for a sol-gel based synthesis of mesoporous TiO 2 , we demonstrate a strategy for the detailed control of the semiconductor morphology on the 10 nm-length scale. The careful adjustment of polymer molecular weight and titania precursor content is used to systematically vary the material structure and its influence upon solar cell performance is investigated. Furthermore, the use of a partially sp 2 hybridized structure directing polymer enables the crystallization of the porous TiO 2 network at high temperatures without pore collapse, improving its performance in solid-state dye-sensitized solar cells.