We have modeled experimental short-circuit photocurrent action spectra of ${\mathrm{poly(3-(4}}^{\mathrm{\prime }}{\mathrm{-(1}}^{\mathrm{″}}{\mathrm{,4}}^{\mathrm{″}}{\mathrm{,7}}^{\mathrm{″}}\mathrm{-trioxaoctyl)phenyl)thiophene)}$ (PEOPT)/fullerene $({\mathrm{C}}_{\mathrm{60}})$ thin film heterojunction photovoltaic devices. Modeling was based on the assumption that the photocurrent generation process is the result of the creation and diffusion of photogenerated species (excitons), which are dissociated by charge transfer at the ${\mathrm{PEOPT/C}}_{\mathrm{60}}$ interface. The internal optical electric field distribution inside the devices was calculated with the use of complex indices of refraction and layer thickness of the materials as determined by spectroscopic ellipsometry. Contributions to the photocurrent from optical absorption in polymer and fullerene layers were both necessary to model the experimental photocurrent action spectra. We obtained values for the exciton diffusion range of 4.7 and 7.7 nm for PEOPT and ${\mathrm{C}}_{\mathrm{60}},$ respectively. The calculated internal optical electric field distribution and resulting photocurrent action spectra were used in order to study the influence of the geometrical structure with respect to the efficiency of the thin film devices. In this way the photocurrent was optimized.

The open-circuit voltage (Voc) of polymer:fullerene bulk heterojunction solar cells is determined by the interfacial charge-transfer (CT) states between polymer and fullerene. Fourier-transform photocurrent spectroscopy and electroluminescence spectra of several polymer:fullerene blends are used to extract the relevant interfacial molecular parameters. An analytical expression linking these properties to Voc is deduced and shown to be valid for photovoltaic devices comprising three commonly used conjugated polymers blended with the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Voc is proportional to the energy of the CT states ECT. The energetic loss q$\Delta${}V between ECT and qVoc vanishes when approaching 0 K. It depends linearly on T and logarithmically on illumination intensity. Furthermore q$\Delta${}V can be reduced by decreasing the electronic coupling between polymer and fullerene or by reducing the nonradiative recombination rate. For the investigated devices we find a loss q$\Delta${}V of $\sim${}0.6$\hskip0.3em${}eV at room temperature and under solar illumination conditions, of which $\sim${}0.25$\hskip0.3em${}eV is due to radiative recombination via the CT state and $\sim${}0.35$\hskip0.3em${}eV is due to nonradiative recombination.

Conjugated polymer actuators can be operated in aqueous media, which makes them attractive for laboratories-on-a-chip and applications under physiological conditions. One of the most stable conjugated polymers under these conditions is polypyrrole, which can be patterned by means of standard photolithography. Polypyrrole-gold bilayer actuators that bend out of the plane of the wafer have been microfabricated in our laboratory. These can be used to move and position other microcomponents. Here we review the current status of these microactuators, outlining the methods used to fabricate them. We describe the devices that have been demonstrated as well as some potential future applications.