**3. Soluble functionalized polyanilines**

**Figure 3.** Ring-opening metathesis copolymerization of fullerene-containing norbornene monomers with related

to metathesis polymerization using a Grubbs catalyst and the products were tested in solar cells. This part of our work was devoted to synthesize new fullerene-containing polymers and copolymers from norbornene-type monomers in the presence of the first-generation Grubbs

Investigated in the work the fullerene-containing norbornene monomers include (**Figure 2**): {(1-methoxycarbonyl)-1-[(2-bicyclo[2.2.1]hept-5-en-2-yl)ethoxycarbonyl]-1,2-methano}-1, 2-dihydro-C60-fullerene (endo:exo = 6:1) **1** [18], {(1-chloro-1-[(2-bicyclo[2.2.1]hept-5-en-2-yl) ethoxycarbonyl]-1,2-methano}-1,2-dihydro-C60-fullerene (endo) **2** [18] and bis[2-{[(2S\*

clo[2.2.1]hept-5-en-2-yl]etoxycarbonyl}-1,2-dihydro-C60-fullerene **3** [19].

)-bicy-

fullerene-free compounds.

88 Emerging Solar Energy Materials

catalyst [(PCy3

) 2 Cl2

RuCHPh].

The development of a new generation of sensor devices is associated primarily with two conductive high-molecular compounds, namely, PANI and polypyrrole, which have been used in highly selective devices for the diagnosis of mixtures of gases and liquids, the so-called "electronic noses" and "electronic tongues" [21]. Biomedical studies of PANI are extremely promising. It has been shown that PANI can be used as a biocompatible electrode: electrical signals supplied to an in-vivo deposited polymer layer encourage the acceleration of tissue regeneration [22]. There is a wide range of already available and potentially possible applications of PANI. Nevertheless, the practical use of this material is limited by a number of serious problems. The first problem is related to the synthesis of PANI with reproducible properties. Samples of the polymer can contain a wide variety of aniline oxidation products with electrical conductivities that differ dozens of times. These products also differ in their spectral and magnetic characteristics and can have a fundamentally different morphology. Such an uncertainty leads to ambiguous results and requires a thorough investigation of the oxidative polymerization of aniline.

The second problem is related to the creation of materials for practical applications. A significant disadvantage of PANI is that it does not melt and is practically insoluble in conventional organic solvents. Therefore, PANI belongs to the category of non-recyclable materials. Furthermore, this polymer is a powder that has no adhesion to other materials.

Concerning this, it is obvious that the synthesis is a key process in the preparation of not only PANI but also PANI-based composites. Despite the apparent simplicity, the oxidative polymerization of aniline is a complex multistage reaction. The conventional procedure for chemical synthesis of PANI includes the oxidative polymerization of the monomer in an aqueous solution of an inorganic acid [23]. These conditions provide the formation of an unmeltable powder that is insoluble in the majority of available organic solvents. In order to eliminate the above disadvantages, PANI can be modified in different ways. An alternative version of the optimization of the performance characteristics of the polymer is the functionalization of the initial monomer rather than of the target product. In particular, the introduction of *o*-toluidine and *o-*anisidine (instead of aniline) into the polymerization process leads to the precipitation of high-molecular compounds soluble in organic solvents. Further, the homopolymer based on *o*-toluidine can be used in the design of electrochromic and photovoltaic devices. There are examples where the electrochemical polymerization of *o*-toluidine was performed with different solutions of acids used as electrolytes. In particular, Borole et al. [24] used sulfuric acid, *n*-toluenesulfonic acid, sulfamic acid and sulfosalicylic acid. A comparative analysis of the synthesized substances demonstrated that the maximum electrical conductivity was exhibited by a polymer soluble in the majority of conventional solvents, which was isolated with the participation of sulfonic acids. In a number of works, the method was proposed for the synthesis of high-molecular compounds with high electrical conductivity and good solubility by varying the ratio of comonomers (electrochemical polymerization). This made it possible to synthesize copolymers based on *o*-anisidine and *o*-toluidine [25]. It was noted that the most stable films are formed from a copolymer in which the content of pyrrole is more than 50% with respect to *o*-toluidine.

The homopolymerization of **12** was carried out by means of its oxidation, which resulted in the formation of a dark-green precipitate of polymer **13** in aqueous solutions of acids. The most frequently used oxidizing agent was ammonium persulfate. It is believed that the use of ammonium persulfate leads to the formation of a high molecular weight polymer with a high

New Organic Polymers for Solar Cells http://dx.doi.org/10.5772/intechopen.74164 91

The oxidation of aniline was performed in an acidic medium with hydrochloric acid at the pH = 0–2 according to the scheme shown in (**Figure 4**). Aniline-derivative copolymers **14–16** were synthesized in different molar ratios of *o*-toluidine and **12** (1:3. 1:1. 3:1, respectively) according to procedures similar to those used for the synthesis of homopolymer **13**. The yield

Electronic conductivity of organic molecular compounds differs from that of metal and inorganic semiconductors such as silicon and germanium. The well-known band theory of crystal lattice is a good base to understand the conduction mechanism of crystalline molecular solids and conjugated and unconjugated polymers. At the same time, the applicability of the ideal elongated chain model to materials with a complicated morphology is naturally limited. Even within the frames of the idealized model, the inorganic conductors and semiconductors differ considerably from polymers. Besides, in polymers, the screening of interactions between charge carriers is less; electron– electron and electron–hole interactions play an important role causing considerable localization of electron states as compared with inorganic materials [27]. Absence of macroscopic ordering means inadequacy of band conduction model to describe electron conductivity of bulk polymer materials, though it can be used to a limited extent when studying the conduction process.

In amorphous layers of thin organic films the terms "conduction band" and "valence band" are usually replaced by the terms of the LUMO and the HOMO, respectively. The states' density is mainly described quite satisfactorily by Gaussian distribution of localized molecular

Depending on the size of barrier on the interface of electrode with polymer film, electric current flowing through the sample can be of injection type, that is, limited by space charge. In this case, one of the electrodes should be an ohmic one, that is, it should provide more charge

electrical conductivity.

of the copolymer was ~80%.

orbitals of individual molecules [28].

**4. Charge transport in thin polymer films**

**Figure 4.** Homopolymerization of 2-(1-methyl-2-buten-1-yl)aniline **12.**

We carried out research identifying the most effective representatives and expanding the range of electrically conductive high-molecular compounds, primarily using functionalized aniline and researching the electrophysical and physicochemical properties of the target products.

Taking into account that the electrical conductivity of a high-molecular compound increases with the elongation of the conjugation chain, we turned to the development of the polymerization process of the functionalized derivative of aniline, rather than the aniline itself, and to the investigation of the physical and physicochemical properties of the obtained products.

The monomer used for the oxidative polymerization was the previously synthesized 2-(1-methyl-2-buten-1-yl)aniline **12** [26] with an alkenyl substituent that occupies the *o*-position of the aromatic ring and increases the conjugation chain. The diversity of the molecular structure, morphology and properties of the oxidation products of aniline is associated with the presence of the main reagents, namely, the monomer and the growing chain in unprotonated and protonated forms, as well as with the existence of two mechanisms of oxidation: the chain reaction of electrophilic substitution and the recombination of cation-radical centers. The contribution from the two reactions depends on the protonation state of the reagents and, consequently, on the pH of the reaction medium.

**Figure 4.** Homopolymerization of 2-(1-methyl-2-buten-1-yl)aniline **12.**

The second problem is related to the creation of materials for practical applications. A significant disadvantage of PANI is that it does not melt and is practically insoluble in conventional organic solvents. Therefore, PANI belongs to the category of non-recyclable materials.

Concerning this, it is obvious that the synthesis is a key process in the preparation of not only PANI but also PANI-based composites. Despite the apparent simplicity, the oxidative polymerization of aniline is a complex multistage reaction. The conventional procedure for chemical synthesis of PANI includes the oxidative polymerization of the monomer in an aqueous solution of an inorganic acid [23]. These conditions provide the formation of an unmeltable powder that is insoluble in the majority of available organic solvents. In order to eliminate the above disadvantages, PANI can be modified in different ways. An alternative version of the optimization of the performance characteristics of the polymer is the functionalization of the initial monomer rather than of the target product. In particular, the introduction of *o*-toluidine and *o-*anisidine (instead of aniline) into the polymerization process leads to the precipitation of high-molecular compounds soluble in organic solvents. Further, the homopolymer based on *o*-toluidine can be used in the design of electrochromic and photovoltaic devices. There are examples where the electrochemical polymerization of *o*-toluidine was performed with different solutions of acids used as electrolytes. In particular, Borole et al. [24] used sulfuric acid, *n*-toluenesulfonic acid, sulfamic acid and sulfosalicylic acid. A comparative analysis of the synthesized substances demonstrated that the maximum electrical conductivity was exhibited by a polymer soluble in the majority of conventional solvents, which was isolated with the participation of sulfonic acids. In a number of works, the method was proposed for the synthesis of high-molecular compounds with high electrical conductivity and good solubility by varying the ratio of comonomers (electrochemical polymerization). This made it possible to synthesize copolymers based on *o*-anisidine and *o*-toluidine [25]. It was noted that the most stable films are formed from a

copolymer in which the content of pyrrole is more than 50% with respect to *o*-toluidine.

consequently, on the pH of the reaction medium.

We carried out research identifying the most effective representatives and expanding the range of electrically conductive high-molecular compounds, primarily using functionalized aniline and researching the electrophysical and physicochemical properties of the target products.

Taking into account that the electrical conductivity of a high-molecular compound increases with the elongation of the conjugation chain, we turned to the development of the polymerization process of the functionalized derivative of aniline, rather than the aniline itself, and to the investigation of the physical and physicochemical properties of the obtained products. The monomer used for the oxidative polymerization was the previously synthesized 2-(1-methyl-2-buten-1-yl)aniline **12** [26] with an alkenyl substituent that occupies the *o*-position of the aromatic ring and increases the conjugation chain. The diversity of the molecular structure, morphology and properties of the oxidation products of aniline is associated with the presence of the main reagents, namely, the monomer and the growing chain in unprotonated and protonated forms, as well as with the existence of two mechanisms of oxidation: the chain reaction of electrophilic substitution and the recombination of cation-radical centers. The contribution from the two reactions depends on the protonation state of the reagents and,

Furthermore, this polymer is a powder that has no adhesion to other materials.

90 Emerging Solar Energy Materials

The homopolymerization of **12** was carried out by means of its oxidation, which resulted in the formation of a dark-green precipitate of polymer **13** in aqueous solutions of acids. The most frequently used oxidizing agent was ammonium persulfate. It is believed that the use of ammonium persulfate leads to the formation of a high molecular weight polymer with a high electrical conductivity.

The oxidation of aniline was performed in an acidic medium with hydrochloric acid at the pH = 0–2 according to the scheme shown in (**Figure 4**). Aniline-derivative copolymers **14–16** were synthesized in different molar ratios of *o*-toluidine and **12** (1:3. 1:1. 3:1, respectively) according to procedures similar to those used for the synthesis of homopolymer **13**. The yield of the copolymer was ~80%.
