**6.1 PV textiles by PV fibres**

This technique is based on the development of photovoltaic fibres using Si-based /organic semiconducting coating or incorporation of dye-sensitized cells (DSC). Availability of PV fibre offer more freedom in the selection of structure for various type of applications35-39.

The development of photovoltaic fibres offers advantages to manufacture large area active surfaces and higher flexibility to weave or knit etc40.

Although, the problem of manufacturing textile structure by using dye-sensitized cells (DSC-PV) fibres into textile structure is still alive and require a optimization with respect to textile manufacturing operations. In a typical research work the working electrode of DSC-PV fibre is prepared by coating Ti wire with a porous layer of TiO2. This working electrode is embedded in an electrolyte with titanium counter electrode. The composite structure is coated with a transparent cladding to ensure protection and structural integrity. The electrons from dye molecules are excited by photo energy and penetrated into the conduction band of TiO2 and move to the counter electrode through external circuit and regenerate the electrolyte by happening of redox reaction. Ultimately the electrolyte regenerates the dye by means of reduction reaction.

The performance of DSC fibre is majorily depends on the grade of TiO2 coating and its integration to Ti substrate. The integrity of Ti with TiO2 will depend on the surface cleanliness and roughness of Ti, affinity between Ti and TiO2 and other defects. The deposition of TiO2 dye on Ti wire surface is performed by strategy as shown in Fig.6. The integrity of coating on Ti substrate is tested by using peel test, tensile test, four point bending test and scratch test. The amount of discontinuities is measured by optional microscopy and SEM41-47.

The photovoltaic potential of dye-sensitized solar cells (DSSC) of Poly(vinyl alcohol) (PVA) was improved by spun it into nanofibers by electrospinning technique using PVA solution containing silver nitrate (AgNO3). The silver nanoparticles were generated in electrospun PVA nanofibers after irradiation with UV light of 310~380 nm wavelength. Electrospun PVA/Ag nanofibers have exhibited Isc , FF, V oc , and *η* showed the values of 11.9~12.5 mA/cm2, 0.55~10.59, 0.70~10.71 V, and 4.73~14.99%, respectively. When the silver was loaded upto 1% as dope additives in PVA solution, the resultant electrospun PVA/Ag nanofibres exhibited power conversion efficiency 4.99%, which is higher than that of dye sensitized solar cells (DSSC) using electrospun PVA nanofibers without Ag nanoparticles48.

of light spectrum contains very little intensity and consequently do not have a major contribution and i.e only 1.4% to the total possible current. It is evident from above discussion that to increase the current realization λmax have to increase from 650 to 1000nm, in turn decreasing the band gap. Poly (3-hexylthiophene) is a typical example of low badgap polymeric material has a band gap of 650nm (1.9 eV) which can harvest up to 22.4% of the available photons. Hence, it is necessary to fabricate the polymers having broad absorption

Photovoltaics and textiles are two different areas where a successful collaboration brings very smart results. The integration of these two different sectors can be possible by adopting

This technique is based on the development of photovoltaic fibres using Si-based /organic semiconducting coating or incorporation of dye-sensitized cells (DSC). Availability of PV fibre offer more freedom in the selection of structure for various type of applications35-39. The development of photovoltaic fibres offers advantages to manufacture large area active

Although, the problem of manufacturing textile structure by using dye-sensitized cells (DSC-PV) fibres into textile structure is still alive and require a optimization with respect to textile manufacturing operations. In a typical research work the working electrode of DSC-PV fibre is prepared by coating Ti wire with a porous layer of TiO2. This working electrode is embedded in an electrolyte with titanium counter electrode. The composite structure is coated with a transparent cladding to ensure protection and structural integrity. The electrons from dye molecules are excited by photo energy and penetrated into the conduction band of TiO2 and move to the counter electrode through external circuit and regenerate the electrolyte by happening of redox reaction. Ultimately the electrolyte

The performance of DSC fibre is majorily depends on the grade of TiO2 coating and its integration to Ti substrate. The integrity of Ti with TiO2 will depend on the surface cleanliness and roughness of Ti, affinity between Ti and TiO2 and other defects. The deposition of TiO2 dye on Ti wire surface is performed by strategy as shown in Fig.6. The integrity of coating on Ti substrate is tested by using peel test, tensile test, four point bending test and scratch test. The amount of discontinuities is measured by optional

The photovoltaic potential of dye-sensitized solar cells (DSSC) of Poly(vinyl alcohol) (PVA) was improved by spun it into nanofibers by electrospinning technique using PVA solution containing silver nitrate (AgNO3). The silver nanoparticles were generated in electrospun PVA nanofibers after irradiation with UV light of 310~380 nm wavelength. Electrospun PVA/Ag nanofibers have exhibited Isc , FF, V oc , and *η* showed the values of 11.9~12.5 mA/cm2, 0.55~10.59, 0.70~10.71 V, and 4.73~14.99%, respectively. When the silver was loaded upto 1% as dope additives in PVA solution, the resultant electrospun PVA/Ag nanofibres exhibited power conversion efficiency 4.99%, which is higher than that of dye sensitized solar cells (DSSC) using electrospun PVA nanofibers without Ag nanoparticles48.

to achieve increase in the efficiency of the solar cell33-34.

There are two basic techniques to manufacture PV textiles.

surfaces and higher flexibility to weave or knit etc40.

regenerates the dye by means of reduction reaction.

following techniques.

**6.1 PV textiles by PV fibres** 

microscopy and SEM41-47.

**6. Different techniques to manufacture photovoltaic textiles** 

Ramier et al., (2008), concluded that the feasibility of producing textile structure from DSC-PV fibre is quite good. The deposition of TiO2 on flexible fibre is expected to be quite fruiteful in order to maintain the structural integrity without comparing with PV performance49.

Fig. 6. A model DSC Photovoltaic fibre by surface deposition

Fibre based organic PV devices inroads their applications in electronics, lighting, sensing and thermoelectric harvesting. By successful patch up between commodity fibre and photovoltaic concept, a very useful and cost effective way of power harvesting is matured50-52.

Coner et al.,53 have developed a photovoltaic fibre by deposition of small Molecular weight organic compound in the form of concentric layer on long fibres. They manufactured the OPV fibre by vacuum thermal evaporation (VTE) of concentric thin films upto 0.48 mm thickness on polyamide coated silica fibre. Different control devices are based on OPV cells containing identical layer structures deposited on polyimide substrates. The OPV based fibre cells were defined by the shape of the substrate and 1 mm long cathodes. All fibre surfaces were cleaned well prior to deposition. Lastly, they concluded that performance of OPV fibre cells from ITO is inferior in terms of changes in illumination angle, enabling the optical photovoltaic (OPV) fibre containing devices to outperform its planar analog under favourable operating conditions. Light emitting devices are designed in such a way that becomes friendly to weave it. The light trapping on fibre surface can be improved by using external dielectric coating which is coupled with protective coating to enhance its service time. Successful PV fibre can be manufactured by opting appropriate material with more improved fabrication potential54.

Dye sensitized solar cells (DSC) are low cost, applicable in wide range of application and simple to manufacture. These merits of dye-sensitized PV fibre makes it a potential alternative to the conventional silicon and thin film PV devices55.

DSC works on the principle of optoelectronically active cladding on an optical fibre. This group was manufactured two type of PV fibre using polymethylmethacrylate (PMMA) baltronic quality diameter 1.3 to 2.0mm and photonium quality glass fibre with diameter 1.0 to 1.5 mm. Both virgin fibre were made electronically conductive by deposition of 130nm thick layer of ZnO:Al by atomic layer deposition technique with the help of P400 equipment. The high surface area photoelectric film for DSC was prepared in two steps. In first step TiO2 in the form of solution or paste having TiO2 nanoparticle is deposited on electronically conductive surface. In the second step dry layer of TiO2 is sintered at 450- 500°C for 30 minute to ensure proper adhesion to the fibre surface. PMMA fibre is suitable to survive upto 85°C. Hence mechanical compression is alternate technique to ensure the fixation.

Flexible Photovoltaic Textiles for Smart Applications 55

film was formed by dip coating and dried at room temperature upto 30 min before proper sintering between 475 to 500°C. Appropriately sintered fibres were then immersed in dye solution consisting of 0.32 ml of the cis-bis(isothiocyanate)bis(2,2-bipyridyl-4-4' dicarboxylato) ruthenium(II) bis-tetrabutyl ammonium, Solaronix SA with trade name N719 dye in absolute ethanol for 48h. The dyeing of nonporous Polymethylmethacrylate (PMMA) fibre coated with nonporous TiO2 layer was performed in the same dye bath. After complete senetization the excess dye was rinsed away with ethanol. A electrolyte solution was prepared with 0.5 M 4 tert butylpyridine and 0.5 M Lil, 0.05MI2 in 3 methoxypropionitrile (MePRN) with 5 wt% polyvinylidene fluoride-hexafluoro-propylene(PVDE-HFP) added as gelatinizing agent as

Finally gelatinized iodine electrolyte was added next with dip coating from hot solution. Lastly the carbon based counter electrode was coated by means of a gel prepared by exhaustive grinding of 1.4g graphite powder and 0.49 grade carbon black simultaneously.

Bedeloglu et al., have used nontransparent PP as substrate. The PP tape was washed using methanol, isopropanol and water and then dried in N2 atmosphere. Thermal evaporation technique was used to deposit 100nm thick Ag contact layer on PP substrate. A filtered solution of PEDOT: PSS, chemical structure shown in Fig.7, in 5% dimethyl sulfoxide (DMSO) and stirred with 0.1% Triton X-100 to increase the thermal conductivity and cohesiveness properties. Stirred mixture of PEDOT: PSS were deposited on cleaned PP tapes at a thickness of 200 nm by dip coating technique. A blend of P3HT as conjugated polymer and PCBM was stirred upto 24h in chlorobenzene and then dip coated with thickness of 200 nm on top of PEDOT: PSS layer. Finishing of all PV structures was completed in vacuum chambers. An aluminium contact layer of approximately 3 nm thickness was deposited followed by 7nm thick Ag layer as anode. The purpose of Al layer was to avoid short circuiting between Ag and

**6.1.1 Manufacturing of photovoltaic fibres as per Bedeloglu et al.,57-58 method** 

PEDOT: PSS films. The resultant photovoltaic fibre is shown in Fig.8.

Fig. 8. Schematic representation of Photovoltaic fibre

used by Wang et al., (2004)56.

Fig. 7. Chemical configurations of (a) PEDOT:PSS (b) P3HT (c) MDMO-PPV (d) PCBM

Glass fibre is capable to withstand with sintering temperatures which inroads the possibilities of preparation of porous photoelectrodes on them. Commercially available TiO2 paste was diluted to achieve appropriate viscosity with tarpin oil to make suitable for dip-coating. TiO2

Fig. 7. Chemical configurations of (a) PEDOT:PSS (b) P3HT (c) MDMO-PPV (d) PCBM

Glass fibre is capable to withstand with sintering temperatures which inroads the possibilities of preparation of porous photoelectrodes on them. Commercially available TiO2 paste was diluted to achieve appropriate viscosity with tarpin oil to make suitable for dip-coating. TiO2

film was formed by dip coating and dried at room temperature upto 30 min before proper sintering between 475 to 500°C. Appropriately sintered fibres were then immersed in dye solution consisting of 0.32 ml of the cis-bis(isothiocyanate)bis(2,2-bipyridyl-4-4' dicarboxylato) ruthenium(II) bis-tetrabutyl ammonium, Solaronix SA with trade name N719 dye in absolute ethanol for 48h. The dyeing of nonporous Polymethylmethacrylate (PMMA) fibre coated with nonporous TiO2 layer was performed in the same dye bath. After complete senetization the excess dye was rinsed away with ethanol. A electrolyte solution was prepared with 0.5 M 4 tert butylpyridine and 0.5 M Lil, 0.05MI2 in 3 methoxypropionitrile (MePRN) with 5 wt% polyvinylidene fluoride-hexafluoro-propylene(PVDE-HFP) added as gelatinizing agent as used by Wang et al., (2004)56.

Finally gelatinized iodine electrolyte was added next with dip coating from hot solution. Lastly the carbon based counter electrode was coated by means of a gel prepared by exhaustive grinding of 1.4g graphite powder and 0.49 grade carbon black simultaneously.
