Rational Synthesis of a Polymerizable Fullerene–Aniline Derivative: Study of Photophysical, Morphological and Photovoltaic Properties§

Abstract

This paper describes the synthesis of a polymerizable, aniline appended fullerene derivative, 3-aminobenzyl-phenyl-C61-butyrate (PCBAn) and its corresponding polymer (P-PCBAn), and detailed photophysical and morphological analysis towards application as an acceptor in polymer solar cells (BHJ-PSCs). The poly-3-aminobenzyl-phenyl-C61-butyrate (P-PCBAn), having a substituted polyaniline (PANI) skeletal structure, was synthesized via FeCl3 oxidative polymerisation of PCBA in its non-conducting leucoemaraldine state. HOMO and LUMO energies estimated using optical and electrochemical techniques revealed upshifted LUMO levels for PCBAn (−3.68 eV, E = 0.1 eV) and P-PCBAn (−3.66 eV, E = 0.12 eV) compared to the parental fullerene derivative, PCBM (−3.78 eV). The morphologies of PCBAn and P-PCBAn individually and in polymer blends with P3HT were investigated using AFM and TEM analysis, which showed nanoflake-like aggregates for P3HT/PCBAn and a favourable interconnected nanonetwork structure for P3HT/P-PCBAn. The wide angle X-ray scattering (WAXS) studies of PCBAn films drop-cast from THF/water (3:7) mixture and P-PCBAn films drop-cast from 1,2-dichlorobenzene exhibited plane reflections of lamellar mesophases with dspacing of 3.4 nm and 3 nm for PCBAn and P-PCBAn, respectively. The fluorescence quenching experiments with P3HT indicated efficient electron transfer from P3HT to P-PCBAn when compared to PCBAn. The fabrication of an inverted BHJ-PSC device using PCBAn and P-PCBAn as an acceptor in combination with P3HT showed PCE of 0.9% and 1.1%, respectively, showing considerable enhancement in the case of the polymeric acceptor. The polymeric acceptor and the rational design strategy used here could open up new opportunities in the PSC device fabrication.