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 main challenge in colloid science is the development of smart delivery systems that store and protect actives from degradation and allow release in response to an external stimulus like temperature. Hollow nanogel capsules made of temperature-sensitive polymers are particularly promising materials. The stimuli-sensitive void size, shell thickness, and permeability determine cargo storage and its release behavior. Thus, determination and control of these morphological parameters are of outmost relevance for the design of new, functional drug delivery vehicles. Here we investigate quantitatively void size and shell thickness of hollow nanogels at different states of swelling by means of small-angle neutron scattering (SANS) employing contrast variation. We demonstrate the structure-sensitivity dilemma: hollow nanogels with a slightly cross-linked shell reveal distinct temperature sensitivity but possess nearly no void (14% of the initial core volume) and are thus hardly “hollow”. Nanogels with a stiff shell are indeed hollow (albeit with smaller void as compared to the core size of the template) but less temperature sensitive.

Homogeneous, cm-scale, plasmonic monolayers with defined plasmon resonance positions and intensities are fabricated by interface assembly of core–shell colloids.

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The temperature-dependence of the hydrodynamic diameter and colloidal stability of gold-polymer core-shell particles with temperature-sensitive (poly(N-isopropylacrylamide)) and temperature-insensitive shells (polyallylaminine hydrochloride/polystyrensulfonate, poly(isobutylene-alt-maleic anhydride)-graft-dodecyl) are investigated in various aqueous media. The data demonstrate that for all nanoparticle agglomeration, i.e., increase in effective nanoparticle size, the presence of salts or proteins in the dispersion media has to be taken into account. Poly(N-isopropylacrylamide) coated nanoparticles show a reversible temperature-dependent increase in size above the volume phase transition of the polymer shell when they are dispersed in phosphate buffered saline or in media containing protein. In contrast, the nanoparticles coated with temperature-insensitive polymers show a time-dependent increase in size in phosphate buffered saline or in medium containing protein. This is due to time-dependent agglomeration, which is particularly strong in phosphate buffered saline, and induces a time-dependent, irreversible increase in the hydrodynamic diameter of the nanoparticles. This demonstrates that one has to distinguish between temperature- and time-induced agglomerations. Since the size of nanoparticles regulates their uptake by cells, temperature-dependent uptake of thermosensitive and non-thermosensitive nanoparticles by cells lines is compared. No temperature-specific difference between both types of nanoparticles could be observed.