**2. Fullerene-containing polymers for organic solar cells**

An important step in improving the efficiency of the OSC was the transition to a bulk heterojunction, which is realized by mixing donor and acceptor materials. The principle of operation of an OSC based on a bulk heterojunction is determined by the fundamental property of polymer materials, which consists of the striving for phase separation at the nanometer level. In the OSC of this type, the donor-acceptor interface, which penetrates the entire volume of the material, ensures the dissociation of excitons, as well as the transport of electrons and

For the first time, solar batteries based on volumetric heterojunction obtained from solutions were reported in 1995. Since then, the number of publications in this field has started to grow

In the early years, poly [2-methoxy, 5-(20-ethyl-hexyloxy)-*p*-phenylene vinylene) (MEH-PPV)/ C60 composites were later replaced by a better processed combination of poly [2-methoxy-5-(30,70-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV)/[6,6]-phenyl-C61/71-butyric acid methyl ester ([60]PCBM or [70]PCBM). Because of the rather large band gap and low mobility of PPV-type polymers, the efficiency at best remained at 3%, and the general interest

Recently, research efforts have focused on poly (alkyl-thiophenes) and in particular on poly (3-hexyl-thiophene) (P3HT). In 2002, the first encouraging results for P3HT: [60]PCBM solar cells at a 1: 3 weight ratio were published. At this time, the short-circuit current density was

A mixture of P3HT: [60]PCBM was and remains dominant in studies of organic solar cells. Consider the material P3HT, which absorbs photons with a wavelength of less than 675 nm (energy of the band gap *Eg* ≈ 1.85 eV). Assuming that in the P3HT: [60]PCBM mixture the polymer determines the optical gap of the composite, it is possible to calculate both the density of the absorbed photons and the absorbed power density. A typical spectrum of light incident on the Earth's surface is given by the standard AM1.5G. This standard defines parameters such

of 4.31 × 10<sup>21</sup> 1/s × m, distributed over a wide range of wavelengths (280—4000 nm) required for the characteristics of solar cells. The P3HT layer: [60]PCBM can absorb, at best, 27% of the available photons and 44.3% of the available power. Despite this, the real efficiency value for

To further increase the efficiency of solar cells, it is necessary to develop donor polymers that absorb light in an even longer wavelength region than P3HT, that is, the absorption boundary should lie at wavelengths greater than 700 nm. Such polymers should have a band gap (the difference in the energies of the lowest unoccupied molecular orbital [LUMO] and HOMO)

The number of known donor polymers providing acceptable light conversion efficiency in photovoltaic cells is still small. In addition to the synthesis of new polymers, work is also under way to obtain new fullerene compounds for the purpose of using them instead of the

(100 mW/cm<sup>2</sup>

) [12].

), and an integrated photon flux

exponentially, and the PCE has increased from 1 to 5% [6–10].

the largest ever observed in an organic solar cell (8.7 mA/cm<sup>2</sup>

an organic solar cell based on P3HT: [60]PCBM does not exseed 5% [13].

in this class of materials disappeared [11].

as an integrated power density of 1000 W/m<sup>2</sup>

of less than 2 eV.

[60]PCBM in photovoltaic cells.

holes to the electrodes.

86 Emerging Solar Energy Materials

The inclusion of fullerene molecules into polymer chains as photo- and electroactive moieties (the subject of intense and competitive research in recent years) should lead to creating new materials with unique structural, electrochemical and photophysical properties. In recent years, many works that extensively use the metathesis strategy to obtain materials for photovoltaic cells have been published [14]. For example, the synthesis of vinyl-type polynorbornenes whose structure contains fragments of [60]PCBM, a conventional electron with drawing component of the active layer in organic photovoltaic cells, was proposed by Eo et al. [15]. Photovoltaic cells where the fullerene-containing copolymer acted as the n-type semiconductor in the active layer were developed based on these polymers. Also of interest are several works [16, 17] in which fullerene-containing monomers (FCMs) were subjected

**Figure 2.** Ring-opening metathesis polymerization of fullerene-containing norbornene monomers.

The ring-opening metathesis polymerization of monomers **1–3** was carried out in the pres-

sphere. In both cases, the consumption of the starting norbornenes **1–3** (TLC monitoring) and

Synthesized homopolymers **4–6** were found to be insoluble in common organic solvents

therefore, it seemed impossible to characterize their structures by spectral methods and to

Note that the results obtained do not contradict the other data available in this field. Some works showed that the incorporation of C60 fullerene into the polymer, in many cases, significantly deteriorates its solubility, which is due to the formation of intermolecular bonds involving polynorbornene fragments and C60 fullerene, as well as due to the restricted solubil-

One of the possible ways to prepare soluble fullerene-containing polymers is involvement of fullerene monomers into copolymerization with highly soluble comonomers. This process is accompanied by the "effect of dilution" of rigid C60-containing units due to the decrease in the concentration of fullerene molecules in the polymer chain, which has a favorable effect on the solubility of the final polymer. To reproduce this effect, norbornenes **1**, **2** and **3** were copolymerized with related fullerene-free compounds 2-[(bicyclo[2.2.1]hept-5-en-2-yl-carbonyl)oxy]ethylmethyl malonate (exo:endo = 6:1) **7** [18, 20], 2-[(2,2-dichloroacetyl)-oxy]ethyl

In all cases, the metathesis polymerization resulted in the formation of copolymers **10, 11**

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

, dimethylsulfoxide) soluble in some organic solvents with good degrees of conversion.

bicyclo[2.2.1]hept5-ene-2-carboxylate (exo:endo = 6:1) **8** [18, 20] and bis[2-{[(2S\*

hept-5-en-2-yl carbonyl]oxy}ethyl)malonate **9** [19], respectively (**Figure 3**).

F and EtOAc), and to swell only partially in dimethyl sulfoxide,

Cl2

in an argon atmo-

89

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

)-bicyclo[2.2.1]

ence of the first-generation Grubbs catalyst at room temperature in CH<sup>2</sup>

(CHCl3

(CHCl3

, C6 H6

, PhMe, C<sup>5</sup>

estimate their molecular weights.

ity of fullerene itself [14].

polymerization of aniline.

H4

**3. Soluble functionalized polyanilines**

the precipitation of the polymers were observed for the first 3 h (**Figure 2**).

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

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 catalyst [(PCy3 ) 2 Cl2 RuCHPh].

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

The ring-opening metathesis polymerization of monomers **1–3** was carried out in the presence of the first-generation Grubbs catalyst at room temperature in CH<sup>2</sup> Cl2 in an argon atmosphere. In both cases, the consumption of the starting norbornenes **1–3** (TLC monitoring) and the precipitation of the polymers were observed for the first 3 h (**Figure 2**).

Synthesized homopolymers **4–6** were found to be insoluble in common organic solvents (CHCl3 , C6 H6 , PhMe, C<sup>5</sup> H4 F and EtOAc), and to swell only partially in dimethyl sulfoxide, therefore, it seemed impossible to characterize their structures by spectral methods and to estimate their molecular weights.

Note that the results obtained do not contradict the other data available in this field. Some works showed that the incorporation of C60 fullerene into the polymer, in many cases, significantly deteriorates its solubility, which is due to the formation of intermolecular bonds involving polynorbornene fragments and C60 fullerene, as well as due to the restricted solubility of fullerene itself [14].

One of the possible ways to prepare soluble fullerene-containing polymers is involvement of fullerene monomers into copolymerization with highly soluble comonomers. This process is accompanied by the "effect of dilution" of rigid C60-containing units due to the decrease in the concentration of fullerene molecules in the polymer chain, which has a favorable effect on the solubility of the final polymer. To reproduce this effect, norbornenes **1**, **2** and **3** were copolymerized with related fullerene-free compounds 2-[(bicyclo[2.2.1]hept-5-en-2-yl-carbonyl)oxy]ethylmethyl malonate (exo:endo = 6:1) **7** [18, 20], 2-[(2,2-dichloroacetyl)-oxy]ethyl bicyclo[2.2.1]hept5-ene-2-carboxylate (exo:endo = 6:1) **8** [18, 20] and bis[2-{[(2S\* )-bicyclo[2.2.1] hept-5-en-2-yl carbonyl]oxy}ethyl)malonate **9** [19], respectively (**Figure 3**).

In all cases, the metathesis polymerization resulted in the formation of copolymers **10, 11** (CHCl3 , dimethylsulfoxide) soluble in some organic solvents with good degrees of conversion.
