Morphological Characterization of Polymer Blends: Impact of Side Chain Modification

Abstract

Conjugated polymers and small molecules have been intensively studied due to their unique electronic and optical properties. Relatively easy and inexpensive fabrication, light weight, mechanical flexibility and non-toxic processing methods open broad prospects for their applications in solar cells[1, 2]. Power conversion efficiency of about 16% [3] has been achieved in these solar cells. Significant focus of research efforts involve develop new materials or to advance processing systems to increase the power conversion efficiency (PCE)[4, 5]. Currently, there remains a question whether the processing based on the nonhalogenated solvents, called "green solvents"[6], is possible on an industrial-scale. The sustainable manufacturing of these organic electronics, because of the organic solvents used, still pose serious health problems and a harmful environmental impact. Here, we studied the morphology of the "green solvents" processed polymer blend and compared with the blend processed with "halogenated solvent" to explore the reasons for the difference in charge generation efficiency in polymer solar cells based on aliphatic side chain and oligoethylene glycol (OEG) side chain[7]. The performance of the highly efficient PPDT2FBT:PCBM [8]system with 9.2% power conversion efficiency is degraded significantly to 1.4% when PCBO12 is blended with a OEG version of a polymer namely PPDT2FBT-A[9], that has only a minor side-chain modification. We employed Atomic Force Microscopy to investigate the impact of side chain on morphology of these polymer blends.