Colloidal particles show interaction with electromagnetic radiation at optical frequencies. At the same time clever colloid design and functionalization concepts allow for versatile particle assembly providing monolayers of macroscopic dimensions. This has led to a significant interest in assembled colloidal structures for light harvesting in photovoltaic devices. In particular thin-film solar cells suffer from weak absorption of incoming photons. Consequently light management using assembled colloidal structures becomes vital for enhancing the efficiency of a given device. This review aims at giving an overview of recent developments in colloid synthesis, functionalization and assembly with a focus on light management structures in photovoltaics. We distinguish between optical effects related to the single particle properties as well as collective optical effects, which originate from the assembled structures.Colloidal templating approaches open yet another dimension for controlling the interaction with light. We focus in this respect on structured electrodes that have received much attention due to their dual functionality as light harvesting systems and conductive electrodes and highlight the impact of interparticle spacing for templating.

A new generation of polythiophene-based polyelectrolytes is reported to address fundamental issues in organic electrochemical transistors (OECTs). In such devices, the semiconductor must be able to transport and store ions and possess simultaneously a very high electronic mobility. For this, the ion-conducting 6-(thiophen-3-yl) hexane-1-sulfonate tetramethylammonium monomer (THS − TMA + ) is copolymerized with the hole-conducting 3-hexylthiophene (3HT) to obtain copolymers, PTHS − TMA + -co-P3HT 1−3 with a gradient architecture. The copolymers having up to 50 mol % 3HT content are easily oxidizable and are crystalline. Consequently, for the copolymers, a higher stability in water is achieved, thus reducing the amount of cross-linker needed to stabilize the film. Furthermore, OECTs using copolymers with 75 and 50 mol % of PTHS − TMA + content exhibit 2−3 orders of magnitude higher ON/OFF ratio and an extremely lower threshold voltage (−0.15 V) compared to PTHS − TMA + . Additionally, high volumetric capacitance (C* > 100 F/cm 3 ) is achieved, indicating that the ion transport is not hampered by the hydrophobic 3HT up to 50 mol %, for which a very high OECT hole mobility of 0.017 cm 2 /(V s) is also achieved. Thus, the concept of copolymerization to combine both ionic and electronic charge transport in an organic mixed conductor offers an elegant approach to obtain highperformance OECT materials.

A series of poly(3-hexylthiophene)-block-poly-(ethylene glycol) (P3HT-b-PEG) with constant P3HT block length block and variable PEG block lengths are presented. Alkyne-functionalized P3HT with high absolute molecular weight of 11.4 kg/mol is combined with azide-functionalized PEGs via copper-catalyzed alkyne−azide cycloaddition (CuAAC). The resulting P3HT-b-PEG block copolymers have PEG weight fractions between 15 and 64 wt %. In bulk materials the crystallinity in the conjugated block is similar to pure P3HT, while the crystallinity of PEG is influenced with decreasing PEG block length. On addition of MeOH as a nonsolvent for the P3HT block, these block copolymers are able to form stable micellar aggregates if the PEG fraction is >31 wt %. In AFM, DLS, and cryo-TEM, P3HT-b-PEG micelles are found to have a spherical or cylindrical shape with diameters of around 25 nm and lengths between 40 nm and some hundred nanometers. It is found that short PEG blocks lead to bigger block copolymer micelles. Thus, a correlation of composition on solution structure and its consequences on the crystallization of both blocks is given.

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