Improvement of the properties of P3HT: PCBM blends using new solvents

Abstract

In this work we report results related to the improvement of optical and structural properties of thin films of P3HT:PCBM blends grown on ITO and FTO substrates by spin coating using new solvents; the effect of annealing and solvent type on the optical and structural properties is evaluated through spectral absorbance, XRD (x-ray diffraction), Raman spectroscopy and fluorescence microscopy measurements. The studies revealed that the use of these new solvents allowed to grow PCBM:P3HT blends with improved properties for use as active layer of organic cells with bulk heterojunction structure. This samples exhibit high degree of crystallographic ordering, high absorbance in the visible region, low fluorescence and proven formation of PCBM/P3HT heterointerfaces. In particular the PCBM:P3HT films prepared using mesitylene based solution have better spectral absorbance and molecular ordering than those prepared using conventional solvents such as chlorobenzene, dichlorobenzene or toluene. Since the P3HT:PCBM blend does not dissolve well in mesitylene at room temperature, thin films of P3HT:PCBM blends were prepared using mixtures of mesitylene and other solvents heated at different temperatures. The results revealed that the blends prepared using pure mesitylene stirred and heated to 100°Cprior to deposition, lead totheformationof cluster free layers with good homogeneity, crystallinity and spectral absorbance.