Comparison of blend morphologies of the nano-patterned photoactive films via two different techniques: thermal-assisted and solvent-assisted soft-nanoimprint lithography

Abstract

In this work, we investigate the blend morphology of nano-patterned P3HT:PCBM mixture films formed by different patterning processes and their effect on the performance of organic photovoltaic cells (OPVCs). Patterns were prepared by thermal and solvent-assisted soft nanolithography using flexible poly(dimethylsiloxane) (PDMS) molds in order to give different patterning conditions. The vertical and lateral phase separation of the blend mixture and the crystallinity and orientation of the polymer chain were examined by various characterization methods, including atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic secondary ion mass spectroscopy (DSIMS) and grazing incident X-ray diffraction (GIXRD). We found that blend morphologies are greatly affected by the patterning conditions which include the modulus and mobility of each component and the interaction between the polymer blend and the mold surface during the patterning procedure. The device prepared by thermal-assisted soft nanoimprint lithography (SNL) showed the highest performance due to the uniform vertical compositional distribution and enhanced vertical conformation and high crystallinity of the polymer chain.