No abstract

A new ordered structure of the C60 derivative PCBM ([6‐6]‐phenyl C61‐butyric acid methyl ester) is obtained in thin films based on the blend PCBM:regioregular P3HT (poly(3‐hexylthiophene)). Rapid formation of needlelike crystalline PCBM structures of a few micrometers up to 100 μm in size is demonstrated by submitting the blended thin films to an appropriate thermal treatment. These structures can grow out to a 2D network of PCBM needles and, in specific cases, to spectacular PCBM fans. Key parameters to tune the dimensions and spatial distribution of the PCBM needles are blend ratio and annealing conditions. The as‐obtained blended films and crystals are probed using atomic force microscopy, transmission electron microscopy, selected area electron diffraction, optical microscopy, and confocal fluorescence microscopy. Based on the analytical results, the growth mechanism of the PCBM structures within the film is described in terms of diffusion of PCBM towards the PCBM crystals, leaving highly crystalline P3HT behind in the surrounding matrix.

A new approach is presented in order to improve the thermal stability of polymer:PCBM bulk heterojunction solar cells. The central idea in this approach is the use of a polymer with high glass transition temperature (T g ), well above the normal operating temperatures of the devices. In this paper a PPV-derivative with a T g of 150°C was used as electron donor and the thermal stability of the obtained solar cells was compared with solar cells based on the reference material Poly[2methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) with a T g of 45°C.The use of the material with higher glass transition temperature resulted in a significant improvement of the thermal stability of the photovoltaic parameters. Furthermore, a systematic TEM study demonstrates that the better thermal stability of performance coincides with a more stable active layer morphology. Both improvements are attributed to the reduced free movement of the electron donor material ([6-6]-phenyl C 61 butyric acid methyl ester, PCBM) within the active layer of the solar cell.1

and in P3HT/TiO 2 junctions after irradiation with E > 1.9 eV.