R. Vishnoi

Surface and structural studies of fullerene C70 under ion irradiation

Thin films of C70 were grown on double side polished silicon substrate by resistive heating of C70 powder. These films were irradiated with 90 MeV Si7+ ions at different fluences in the range from 1 × 1012 to 6 × 1013 ions cm−2. The investigations on structural and surface modifications were made (after irradiation) by Raman spectroscopy and atomic force microscopy (AFM), respectively. Raman spectroscopic studies reveal that C70 is not completely transformed into amorphous carbon at a fluence of 6 × 1013 ions cm−2. Swift heavy ion irradiation generates nanometre size conducting tracks in fullerenes. For 90 MeV Si ions irradiated C70 fullerene, the damage cross-section (σ) and radius of damaged cylindrical zone were estimated from Raman spectra, to be ∼0.32 × 10−13 cm2 and ∼1.01 nm, respectively, using vibrational modes of C70. From AFM study it is clear that the film irradiated at a fluence of 3 × 1012 ions cm−2 shows maximum roughness. Contact angle measurements have been performed to know about hydrophilic or hydrophobic nature of fullerene C70 thin films.

Fabrication, characterization and annealing of polymer-fullerene bulk heterojunction organic solar cells

The structural and optical properties of bulk heterojunction (BHJ) organic solar cell devices have been studied before and after heat treatment. The BHJ structure is fabricated by making the blend of Poly [3-hexylthiophene] (P3HT) and Phenyl C61 butyric acid methyl ester (PCBM) for active layer. After the heat treatment at 140 °C temperature, the device is characterized by X-ray diffraction (XRD) measurement, Raman spectroscopy and UV-visible absorption spectroscopy. The reduced intensity of XRD peak corresponding to (100) plane and decreased crystallite size was observed after annealing. The Raman peak intensity corresponding to C=C stretching mode and optical absorption peak intensity is also found to be reduced after the heat treatment to the device. The diminished intensitiesafter annealing may be due to diffusion of Al into active layer.