Highly Electro-Conductive Thiophene and N-methylpyrrole functionalized hyperbranched polypropylenimine tetramine-co-poly(3-hexylthiophene-2,5-diyl) donor materials for organic solar cells

Poly(3-hexylthiophene-2,5-diyl) (P3HT) chains were grown on the surface of thiophene functionalized polypropylenimine tetramine (PPI-TH) and N-methylpyrrole functionalized polypropylenimine tetramine (PPI-PY) using chemical oxidation polymerization. After growing the P3HT chains on the surface of PPI-TH and PPI-PY, the properties of the resulting co-polymers were compared with those of linear P3HT as a reference. P3HT, poly(3-hexylthiophene-2,5-diyl)-co-thiophene functionalized polypropylenimine tetramine (P3HT-T), and poly(3-hexylthiophene-2,5-diyl)-co-N-methylpyrrole functionalized polypropylenimine tetramine (P3HT-P) were characterized by nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), ultraviolet-visible spectroscopy (UV-Vis), scanning electron microscope (SEM), photoluminescence and electrochemical methods. P3HT-T and P3HT-P showed new imine bands on FTIR spectra, change in morphology and optical bandgaps, Stokes shifts, decrease in LUMO energy gap values, and increase in conductivity compared to P3HT. In addition, organic solar cells (OSCs) based on P3HT, P3HT-T, and P3HT-P as donor materials are discussed in this work. In comparison with P3HT-based OSC, the P3HT-T and P3HT-P based OSCs have improved performance due to an increase in VOC and FF. Electrochemical impedance spectroscopy (EIS) and Tafel plots confirmed a reduction in charge recombination and an increase in charge transport for P3HT-T and P3HT-P devices.