Novel conductive multi-walled polymeric nanotubes of poly(diazoaminobenzene) for single-layer polymer solar cell
Graphical abstract
Introduction
The photoisomerization of the azo chromophores has been a topic that has caught the attention of researchers in a wide variety of research fields [[1], [2], [3], [4], [5], [6], [7], [8]]. There has been a demand to understand the role of chromophores on changing the properties of these polymeric materials. It is known that the azobenzene segment employs as a trigger for the introduction of the morphological changes. Based on these studies, it is now known that the presence of an azo chromophore can modulate both electroactivity and photoactivity of polymers. The application of different conducting polymers such as polypyrrole, polythiophene, polyphenylene and polyaniline (PANI) have been reported for devepoling of green and renewable energy with solar cells due to the presence of a conjugated π-electron backbone [[9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]]. The synthesis of conjugated polymers such as azo-linked materials has been reported with various synthetic routes in the literature [7] but their applications in solar cells have been limited. Synthesis of azo-linked polymers with solubilizing alkyl side chains based on thiophene and fluorene as well as using palladium and copper-catalyzed polymerizations have been reported previously [[22], [23], [24], [25]]. These conductive polymers make up a novel class of organic electronic materials that can be utilized for various applications such as drug delivery [26], transistors, sensors, optical storage [27], LED and solar cells [28]. Based on these discoveries, the morphology of polymers has become one of the important factors for increasing the power conversion efficiency (PCE or %η) of polymer solar cells [29]. Yang et al. [30] have reported the effect of morphology of poly(3-hexylthiophene) and methanofullerene derivatives in solar cells. Based on this study, the high performance of polymers were dependent on the crystal structure and mixing them at varying temperatures to prepare a smooth layer. The same result was reported by Shao et al. [31] and van Duren et al. [32]. Chang et al. [33] have also reported 26% increase in PCE photovoltaic performance for an acid-doped PANI nanotube layer. These reports described that the photovoltaic performance of PANI improved with the annealing of polymer layer due to the increase in conductivity and mobility as well as the controlled tubular nanoscale morphologies. Dye-sensitized solar cells (DSSCs) using PANI–ZnS and PANI-CdS nanotubes have been reported [34,35]. Park et al. [36] have reported DSSCs by using porous PANI nanotubes as a counter electrode. The effect of different factors in the fabrication of nanostructures of the conjugated polymers in organic solar cells was reported by Chen and Hsu [37]. Also, the morphological effect of TiO2 nanoparticles and PANI nanofibers on the photovoltaic activity as a new nano-composite of (PANI nanofibers)/(TiO2 nanoparticles) with different architectures have been recently reported by our research group [38]. In the organic and hybrid (organic-inorganic) solar cells, both multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNT) were used for increasing electron tranfer rate. SWCNTs and MWCNTs have different functions due to differences in their band gap [39,40]. The dispersion and orientation of the CNTs in the organic matrix and their effect on the efficiency of solar cells were discussed by Aernouts et al. [41].
DSSCs including azo group compounds have been reported [[42], [43], [44], [45], [46], [47]], but there is no report about their application in the single-layer polymer solar cells, to the best of our knowledge. Meena et al. [48] have recently reported the application of the azo linkage in a multi-layer cell as a main chain with PCE of 0.53%.
Diazoaminobenzene (DAAB) or 1,3-diphenyltriazene is an aromatic amine which has been used for the preparation of several important complexes due to its high concentration of nitrogen atoms [[49], [50], [51], [52]]. Because of its nitrogen double bond (N=N), the photochemistry and cis-trans isomerization of DAAB has been examined [[53], [54], [55]]. In our previous reports, PANI with a nanostructure and poly(p-aminoazobenzene) nanosheets were assembled in the structure of polymer single-layer solar cells [56,57]. To the best our knowledge, there is no report for polymerization of DAAB. In this study, for the first time, a novel conductive poly(diazoaminobenzene) (PDAAB) with multi-walled polymeric nanotube (MWPNT) morphology was synthesized and characterized. The synthesis method developed for MWPNTs of PDAAB is a template-free and green one. In addition, MWPNTs were utilized in the development of single-layer polymer solar cells and their photovoltaic properties were investigated in detail and compared with others reported in literature.
Section snippets
Materials and equipment
Reagents of analytical grade were used without any purification except for aniline, which was purified by distillation. Diazoaminobenzene monomer was purchased from Sigma-Aldrich (Oakville, ON) and also, it was synthesized following the literature method [58]. A JASCO Fourier transform infrared spectrophotometer (Easton, MD) and a Shimadzu UV–visible spectrophotometer (Kyoto, Japan) were used for recording the spectra. An ECS 4010 Nitrogen/Protein Analyzer (Costech Analytical Technologies,
FT-IR analysis
Fig. 2 displays the FT-IR spectra of PDAAB and DAAB. The broad peaks for PDAAB exhibited to the vibrational modes in polyaniline. Similar observations were reported in literature [38,[62], [63], [64], [65]]. The NH bonds indicated stretching absorption at 3000–3200 cm−1 and the Raman active CC ring stretching vibration at 1603 cm−1.
It is known when the protonation induced the conformational changes in the polymer chain, the infrared-inactive modes became infrared-active, which indicated that
Conclusions
In this study, for the first time, the polymerization of the monomer diazoaminobenzene is reported to produce a novel PDAAB via a very simple, one-pot, green, acid and template-free method at room temperature. The synthetic method involves pH-falling and rapid-mixing in the presence of aniline as an initiator at room temperature. The aniline has a critical role in the onset of the reaction and the polymer cannot be formed in the absence of it. Based on these results, PDAAB was observed to have
Data availability statement
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.
Declaration of Competing Interest
The authors declare no conflict of interest.
Acknowledgments
The authors acknowledge the financial support of a grant from the Graduate Council of University of Sistan and Baluchestan and the National Nanotechnology Initiative of Iran. K. K. gratefully acknowledges Canada Research Chair Tier-2 award in "Bioelectrochemistry of proteins" (project no. 950-231116), the Ontario Ministry of Research and Innovation (Project no. 35272), Discovery Grant (project no. 3655) from the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canada
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