Elsevier

Synthetic Metals

Volume 255, September 2019, 116115
Synthetic Metals

Synthesis and characterization of poly(p-aminoazobenzene) nanosheet as a new derivative of polyaniline containing azo groups under green chemistry condition and its high efficiency in solar cell

https://doi.org/10.1016/j.synthmet.2019.116115Get rights and content

Highlights

  • The synthesis of a new derivative of polyaniline containing azo group; poly(p-aminoazobenzene) (PPAAB).

  • The first report of preparation of nanosheets from PPAAB.

  • The monitoring the process of trans↔cis photoisomerization of the azobenzene segments by UV–vis spectroscopy.

  • The first report of the polymer solar cell (PSC) fabrication of PPAAB as FTO/TiO2/PPAAB/Al with a high the PCE (η).

  • Both preparation of polymer and fabrication of PSC are inexpensive, simple, and under a green condition.

Abstract

In recent years, the isomerization of the Ndouble bondN double bonds in two forms, namely the cis (Z) and trans (E) isomers, of aromatic azobenzenes have attracted great interest. It occurs readily both photochemically and thermally. Thus, aromatic azobenzenes are excellent candidates as molecular switches to build dynamic molecular devices. In this paper, synthesis of poly(p-aminoazobenzene) (PPAAB)1 nanosheets as a new derivative of polyaniline containing azo groups by polymerization of diazoaminobenzene as the monomer was conducted in a new, simple and green condition with %72 yield. This is the first report of in-situ polymerization of p-aminoazobenzene (PAAB) with nanosheet morphology via one-pot route and without application of any template. The PPAAB was characterized and its properties were investigated. The photoisomerization process of the polymer was observed by UV–vis spectroscopy under irradiation at 380 nm for 2 h. This polymer demonstrated good thermal stability and the conductivity about 3.4 × 10−4 S cm-1. The XRD analysis showed that the polymer has a semi-crystalline structure. SEM and TEM images also indicated the same results and demonstrated two-dimensional nanosheet morphology with sheet size ranging from 150 nm to several micrometers and thickness about 90 nm. Furthermore, the polymer solar cell (PSC) of PPAAB as FTO/TiO2/PPAAB/Al was fabricated and the power conversion efficiency (η) was obtained about 1.5%. The result showed that the PSC is completely efficient with a high η in comparison with similar cells in literature with less fabrication costing, simple structure, and under a green condition.

Introduction

Polymers that contain azobenzene groups have various applications including the optical devices to convert the wavelength of light, data detection, in computational optical techniques, and many other applications in other fields [[1], [2], [3], [4], [5], [6]]. The p-aminoazobenzene (PAAB)2 is one of the favorite amino aromatic compounds that can be polymerized by different methods such as electrochemical and chemical methods. However, there are few papers on the synthesis of poly(p-aminoazobenzene) (PPAAB). Abd El-Rahman et al. demonstrated that the oxidative electropolymerization of PAAB on glassy carbon in acetonitrile containing pyridine and NaClO4 as a supporting electrolyte result in porous and fibrous polymer films [7]. Jackowska et al. prepared PPAAB films on disc electrodes or Au wire (0.2 cm2 or 0.1 geometric area) from acetonitrile solution containing pyridine, LiClO4 and PAAB [8]. In 2009, Durgaryan et al. synthesized PPAAB via chemical oxidation polymerization in boiling ethanol and under the action of iodine at the equimolar reagent ratio. They also studied the dependence of the yield and the molecular mass of polymer on the acidity of the PAAB polymerization medium in the presence of potassium hydrocarbonate and calcium carbonate [9]. Huang et al. have synthesized PPAAB using ammonium persulfate at below 5 °C in HCl, and investigated the photoisomerization process of the compound by UV–vis spectrum [10]. In our best knowledge, another report on the synthesis of this homopolymer has not been provided by chemical methods, and just few primary studies have been carried out about this polymer and its various methods of synthesis. In this paper, we have synthesized the PPAAB at room temperature, in water as a solvent and without the presence of an acid, for the first time, which is the quite environmentally friendly procedure and a green chemistry method. In addition, the application of this method of synthesis resulted in nanosheet morphology using no template while such a morphology for this polymer has not ever been reported. Also, azobenzene is a famous chromophore that is sensitive to light and cis-trans isomerization can easily occur by photoisomerization. In order to meet the demands of changing the role of polymer materials from structural to functional ones, the current trend is to employ the azobenzene moiety as a “trigger’’ to induce morphological changes which can be light-driven [[11], [12], [13], [14], [15], [16], [17], [18]]. Hence, if azo chromophores are introduced into a polymer, the functional groups would endow the polymer with not only electroactivity but also photoactivity.

This kind of polymers is attractive for scientist since the property of photoactivity in polymers bearing azobenzene group leads to potential application in photonics [[19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29]]. In this paper, UV–vis spectroscopy was employed for monitoring the process of photoisomerization in the synthesized polymer and the photoisomerization behavior was observed.

Also, the azo polymers can be applied in drug delivery [30], as thin film transistors, sensors, optoelectronic devices such as optical storage [31], polymer light emitting diodes and solar cells [32]. Recently, among the applications mentioned above, solar cells are highly regarded by scientists. The compounds containing the azo groups have been widely used in the dye-sensitive solar cell [[33], [34], [35], [36], [37], [38]], but there is not any research done on the use of these polymers in single layer polymer solar cell. However, only the existing report is by Meena et al. that obtained a power conversion efficiency (PCE) of 0.53% by new polymers containing azo linkage as a part of the main chain in multilayers cell (blend with C71-PCBM as a photoactive layer in ITO/PEDOT:PSS/azo linked polymer:C71-PCBM/Al) [39]. Indeed, azo linked polymers can potentially give rise to strongly light absorbing chromophores which are suitable for use in polymer solar cells (PSCs) [39].

Due to the structure, morphology, and conductivity of the synthesized polymer, it possesses the potential to be used in various areas such as solar cells and sensors. So, the polymer solar cell was fabricated by PPAAB with FTO/TiO2/PPAAB/Al structure and the efficiency of PPAAB on the solar cell performance was investigated. Thus, in this paper, along with the synthesis and characterization of this new polymer, a report is presented on its high efficiency in the solar cell.

Section snippets

Materials and equipment

All chemical reagents were prepared from Fluka, Aldrich, and Merck and used as received except for aniline, which was distilled to purify.

FT-IR spectra of the samples were taken by a JASCO spectrophotometer between 450 and 4000 cm−1 from KBr pellets. The Shimadzu spectrophotometer was used to record the Ultraviolet-visible (UV–vis) spectra between 200 and 800 nm by preparing a dilute solution of product (0.02 g L−1) in N-methylpyrrolidone (NMP) during irradiation at about 380 nm every 30 min

FT-IR spectra

The FT-IR spectra of PAAB and PPAAB are shown in Fig. 1. In both spectra, the absorption at 3200-3500 cm−1 is assigned to the stretching of the Nsingle bondH bond. However, the FT-IR spectrum of the monomer shows three peaks while the PPAAB shows a single broad peak because of the stretching of the Nsingle bondH bond similar to the data previously reported for polyaniline [[45], [46], [47], [48], [49], [50], [51]]. The peaks at 1580-1620 cm−1 in PAAB spectra are assigned to stretching of Csingle bondC or bending of the Nsingle bondH

Conclusions

In summary, we have prepared poly(p-aminoazobenzene) (PPAAB) a new derivative of polyaniline containing azo groups by polymerization of diazoaminobenzene as the monomer in green condition. The polymer exhibited good thermal stability, conductivity in the range of semi-conductive compounds and nanosheet morphology. Moreover, it exhibited photoinduced isomerization behavior arisen from azobenzene groups. It seems that the isomerization properties depend on the structure and morphology of the

Acknowledgments

The authors acknowledge the financial support of a grant from the Graduate Council of University of Sistan and Baluchestan and National Nanotechnology Initiative funded by the Iranian government.

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