A summary of the most important technological applications employing reduced graphene oxide.

Sowing the seeds: A simple strategy based on self-seeding allows large single crystals of long regioregular poly(3-hexylthiophene) chains to be grown from solution. When appropriately crystallized, materials differing in their degrees of regioregularity and molecular weights formed monoclinic form II crystals with interdigitated hexyl side groups (see picture).

It is commonly accepted that in order to develop high-performance organic and/or hybrid organic−inorganic solar energy devices, it is necessary to use, among other components, an active donor−acceptor layer with highly ordered nanoscale morphology. In an idealized morphology, the effectiveness of internal processes including exciton generation and separation and charge carrier migration is optimized, leading to an efficient conversion of photons to electricity. With this idea in mind, we have rationally designed and developed an ordered nanoscale morphology consisting of self-assembled poly(3-hexylthiophene) donor domains of molecular dimension, each of them separated by fullerene C60 hydroxide acceptor domains. A poly(3-hexylthiophene)-block-poly(l-lactide) block copolymer was used as a structure-directing agent to pattern active material into ordered nanostructures. Using this intimate morphological control, one can begin to probe structure−property relationships with unprecedented detail with the ultimate goal of maximizing the performance of future organic/hybrid photovoltaic devices.

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All-conjugated block copolymers have significant potential for solution-processed optoelectronic applications, in particular those relying on a p/n junction. Herein, we report the synthesis and structure of all-conjugated diblock copolymers poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene) and poly (3-hexylthiophene)-block-poly(9,9-dioctylfluorene-co-benzothiadiazole) in thin films and in the bulk. The diblock copolymers are prepared using a combination of Grignard metathesis polymerization and Suzuki polycondensation and characterized with NMR spectroscopy, size-exclusion chromatography, multiangle laser light scattering, and UV/vis spectroscopy. Structure in thin films and in the bulk is characterized using differential scanning calorimetry, X-ray diffraction, small-angle X-ray scattering, and atomic force microscopy. Diblock copolymer thin films self-assemble into a crystalline nanostructure with some long-range order after extended solvent annealing, and X-ray scattering measurements show that powder samples exhibit crystallinity throughout the bulk. By temperature dependent X-ray scattering measurements, we find that diblock copolymers self-assemble into crystalline nanowires with phase segregated block copolymer domains. These measurements show all-conjugated diblock copolymers may be useful for achieving solution-processed active layers in organic photovoltaics and light-emitting diodes with optimized structural and photophysical characteristics.

We report the local UV-Vis absorption behaviour of single crystals of conjugated poly-3-hexylthiophene (P3HT), obtained by crystallization in dilute solutions at elevated temperatures based on a self-seeding approach and characterized by high internal structural order. Conjugated polymers represent promising active systems for a variety of optoelectronic applications, such as solar cells, 1 light emitting diodes, 2 eld-effect transistors, 3-5 etc. However, the performance of these materials in such devices has so far oen remained poor, mostly due to the difficulties in controlling molecular conformations, structural packing, and morphology 6,7 of these polymers. In order to correctly interpret and nally to improve the functional behavior of conjugated polymers, it is thus necessary to unravel the relationship between the light absorption properties and molecular conformation or polymer microstructure. As a suitable model system for a systematic study of such structure-optoelectronic property relations, we have recently identied highly ordered single crystals of conjugated poly-3-hexylthiophene (P3HT) of weight average molecular weight of 26 400 g mol À1 , characterized by a unique molecular conformation on all length-scales. 8 They were obtained via crystallization in solution by a self-seeding technique. These crystals are composed of closely packed, p-p stacked (p-p distance of $0.33 nm) fully extended chains which are oriented perpendicular to the substrate. 8

In this work, we report a comparative analysis of the infrared and Raman spectra of octa(3-hexylthiophene) (3HT) 8 , trideca(3-hexylthiophene) (3HT) 13 , and poly(3-hexylthiophene) P3HT recorded in various phases, namely, amorphous, semicrystalline, polycrystalline and single crystal. We have based our analysis on the spectra of the (3HT) 8 single crystal (whose structure has been determined by selected area electron diffraction) taken as reference and on the results of DFT calculations and molecular vibrational dynamics. New and precise spectroscopic markers of the molecular structures show the existence of three phases, namely: hairy (phase 1), ordered (phase 2), and disordered/amorphous (phase 3). Conceptually, the identified markers can be used for the molecular structure analysis of other similar systems.

It is increasingly obvious that the molecular conformations and the long-range arrangement that conjugated polymers can adopt under various experimental conditions in bulk, solutions or thin films, significantly impact their resulting optoelectronic properties. As a consequence, the functionalities and efficiencies of resulting organic devices, such as field-effect transistors, light-emitting diodes, or photovoltaic cells, also dramatically change due to the close structure/property relationship. A range of structure/optoelectronic properties relationships have been investigated over the last few years using various experimental and theoretical methods, and, further, interesting correlations are continuously revealed by the scientific community. In this review, we discuss the latest findings related to the structure/optoelectronic properties interrelationships that exist in organic devices fabricated with conjugated polymers in terms of charge mobility, absorption, photoluminescence, as well as photovoltaic properties.