Film morphology effects on the electrical and optical properties of bulk heterojunction organic solar cells based on MEH-PPV/C60 composite

The influence of film morphology on the electrical behaviour of an MEH-PPV/C60 organic solar cells has been investigated. The dissociation of photogenerated charge pairs in composites of buckminsterfullerenes (C60) in a conjugated polymer matrix (MEH-PPV) forming dispersed heterojunctions was studied at low C60 acceptor concentrations to separate electron transfer from charge transport effects. The motivation of this study was to analyse the strong dependence of organic solar cell efficiencies on the morphology of the composite. Two effects controlling film morphology have been investigated; the first one being the influence of the fullerene concentration and the second one is the effect of the organic solvent used to deposit the photoactive layer. The sample morphology was studied using atomic force microscopy (AFM). Photoluminescence (PL) experiments and current-voltage (I-V) measurements were performed on the deposited photovoltaic film to investigate the influence of dispersion on the charge transfer process between MEH-PPV and C60. An attempt to explain all the results will be presented.