Polymer layers can exhibit significantly improved performances if they possess a multicomponent phase-separated morphology. We present two approaches to control the dimensions of phase separation in thin polymer-blend layers; both rely on polymer nanospheres prepared by the miniemulsion process. In the first approach, heterophase solid layers are prepared from an aqueous dispersion containing nanoparticles of two polymers, whereas in the second approach, both polymers are already contained in each individual nanoparticle. In both cases, the upper limit for the dimension of phase separation is determined by the size of the individual nanoparticles, which can be adjusted down to a few tens of nanometres. We also show that the efficiencies of solar cells using two-component particles are comparable to those of devices prepared from solution at comparable illumination conditions, and that they are not affected by the choice of solvent used in the miniemulsion process.

A miniemulsion process has been used to create layers of conjugated semiconducting polymers from aqueous suspensions. Layers of particles with sizes ranging between 70 and 250 nm can be formed and annealing results in coalescing of the particles into large homogeneous domains (see Figure for a photoluminescence image of a Me‐LPPP layer).

Polymer solar cell devices with nanostructured blend layers have been fabricated using single- and dual-component polymer nanospheres. Starting from an electron-donating and an electron-accepting polyfluorene derivative, PFB and F8BT, dissolved in suitable organic solvents, dispersions of solid particles with mean diameters of ca. 50 nm, containing either the pure polymer components or a mixture of PFB and F8BT in each particle, were prepared with the miniemulsion process. Photovoltaic devices based on these particles have been studied with respect to the correlation between external quantum efficiency and layer composition. It is shown that the properties of devices containing a blend of single-component PFB and F8BT particles differ significantly from those of solar cells based on blend particles, even for the same layer composition. Various factors determining the quantum efficiency in both kinds of devices are identified and discussed, taking into account the spectroscopic properties of the particles. An external quantum efficiency of ca. 4% is measured for a device made from polymer blend nanoparticles containing PFB:F8BT at a weight ratio of 1:2 in each individual nanosphere. This is among the highest values reported so far for photovoltaic cells using this material combination.

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Undercooling and crystallization in stable nanodroplets with a narrow size distribution were analyzed using differential scanning calorimetry (DSC) measurements. Hexadecane droplets in water and NaCl solution droplets in petrolether were prepared using the miniemulsion process. It was found that the undercooling required to obtain crystallization in such droplets is significantly increased, compared to the bulk material: for the hexadecane droplets, a shift from 12 °C (bulk) to approximately -4 °C (droplets) is observed, and for the NaCl solution, a shift from -22 °C (bulk) to -46 °C (droplets) is observed. This is explained by the fact that, in miniemulsions, each droplet must be nucleated separately and the nucleation mechanism is shifted from heterogeneous to homogeneous nucleation. The undercooling additionally increases as the temperature decreases, which is explained with finite size effects for spinodal decompositions. The interfacial tension does not have any influence on the crystallization process. It was found that the crystallization rate in miniemulsion droplets is higher than that of the bulk and is proportional to the droplet size.

The fabrication of organic light‐emitting devices (OLEDs) from semiconducting polymer nanospheres (SPNs) deposited from aqueous dispersions is described. It is found that the active device layer consists of a homogeneous single layer of light‐emitting SPNs. The OLEDs exhibit an electroluminescence onset at the SPN energy gap, which can be attributed to field‐enhanced charge‐carrier injection at the nanostructured Al cathode.

Undercooling and crystallization of different alkanes in stable nanodroplets with narrow size distributions were analyzed by using DSC measurements. The crystal structure was determined by X-ray measurements. Alkane droplets with a defined size between 100 and 500 nm in water were prepared by using the miniemulsion process. The required undercooling to obtain crystallization in such droplets is significantly increased compared to that for the bulk material since the nucleation mechanism is shifted from heterogeneous to homogeneous nucleation. For the even alkanes (C18−C24), a structure change from the triclinic in the bulk to orthorhombic structure in small droplets (100 nm) was detected and attributed to confinement effects inside the droplets. An intermediate rotator phase is of less relevance for the nanosized droplets. For odd alkanes, a strong temperature shift of the crystallization point compared to the bulk system was detected, but no structure change was observed. Both in bulk and in miniemulsion droplets an orthorhombic structure was formed.

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