Unravelling the monomer molar ratio modulation of the optoelectronics of Poly(propylene imine) tetra(thiophen-2-ylmethylene-amine)-co-poly(3-hexylthiophene-2,5-diyl) copolymer

Abstract

Tuning the molecular structure of a copolymer is of considerable importance for optimizing its optoelectronic and morphological properties. This will enormously help in improving and understanding the performance of a copolymer as a donor material in organic photovoltaic cells (OPVs). Herein, we reported a simple synthetic approach for developing a polypropylene imine tetra(thiophen-2-ylmethylene-amine)-co-poly(3-hexylthiophene-2,5-diyl) (P3HT-PT) using chemical oxidation polymerization. To the best of our knowledge, the investigations of monomer molar ratio have never been reported for synthesis of dendritic copolymers. Different concentrations of hexylthiophene (3HT) as a monomer for poly(3-hexylthiophene (P3HT) chains growth on the branches of polypropylene imine tetra(thiophen-2-ylmethylene-amine) (PPIT) as a dendritic core were studied. Nuclear magnetic resonance spectroscopy (NMR) confirmed that P3HT-PT has mixture of P3HT chains arrangements with different chain lengths. More head-to-tail arrangement was achieved at low concentration of 3HT. This study revealed that concentration of 3HT alter with optical, microscopic, electrochemical and thermal properties of P3HT-PT. Synthesized P3HT-PT polymers were further investigated as donor materials in OPVs. The investigations indicated that the P3HT-PT40 based OPV has better photovoltaic performance due to fewer aggregates and high crystallinity of P3HT-PT40, low LUMO energy levels offset and sufficient charge separation in comparison with P3HT-PT60 and P3HT-PT80 based OPVs.