Alcohol soluble cyanopyridine based conjugated donor-acceptor polymers: Synthesis, photophysical and their charge transport behavior

• Published in: European polymer journal 2017-10, Vol.95, p.1-10
• Main Authors: Hemavathi, B., Geetha, Balakrishna R., Ahipa, T.N.
• Format: Article
• Language: English
• Subjects: Addition polymerization; Amine functionalised polymer; Charge transport; Chemical synthesis; Chromatography; Electrodes; Energy levels; Heck polymerisation; Liquid chromatography; Methanol; Photovoltaic cells; Polymer films; Polymers; Polyphenylene vinylene; Potential energy; Solar cells; Solubility; Spectral emissivity; Studies; Substrates; Thermal stability; Thermogravimetric analysis; Thin films; Toluene; Weight reduction
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2017.07.035

[Display omitted] •Two new D-A polymers flanked with amine side chain were synthesized via Heck polymerization.•Polymers are soluble in polar solvent like methanol and insoluble in toluene and dichlorobenzene.•Polymer thin films coated on ITO substrate disclose good transparency.•Polymers showed better hole mobility in the order of ∼1.0×10−6 cm2V−1S−1. Two polymers (PCT1 and PCT2) bearing cyanopyridinyl (as acceptor) and phenylene or fluorenyl (as donor) tethered with N,N-dimethylaminopropyl group (as side chain) were synthesized via Heck polymerisation technique. Both the polymers exhibit an excellent solubility in methanol and insolubility in solvents like toluene and dichlorobenzene. This specific solubility of polymers helps to avoid the intermixing of successive layers during solution processing of solar cells. Further, gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and photophysical studies confirm that these polymers are having high molecular weight, high thermal stability, low optical band gap and blue light emissive nature. In addition, optical transmittance spectra of polymer thin films coated on ITO substrate disclose the transparency of 90%, which is better compared to that of poly(3,4-ethylenedioxythiophene) film (80% transparency). Furthermore, hole only mobility of polymers were investigated by c-AFM method and a mobility of 1.1×10−6 and 1.3×10−6 cm2V−1S−1 were obtained for PCT1 and PCT2, respectively. Here, the obtained mobility values are better compared to other PPV polymers which are reported to be in the order of 10−7cm2V−1S−1. More importantly, ultraviolet photoelectron spectroscopy studies reveal that the polymers coated on ITO have a very high work function of 5.45–5.50eV, thereby minimizes the energy level difference between the electrode and photoactive organic material (typically 5.7 to 6.3eV). As a whole, the utilization of these polymers as interfacial layer at the interface of ITO/active layer can reduce the potential energy loss in solar cells.