**1. Introduction**

42 Solar Cells – New Aspects and Solutions

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In recent years alternative renewable energies including that obtained by solar cells have attracted much attention due to exhaustion of other conventional energy resources especially fossil-based fuels. Photovoltaic energy is one of the cleanest, most applicable and promising alternative energy using limitless sun light as raw material. Even though, inorganic solar cells dominate in the world photovoltaic market, organic solar cells as the new emerging photovoltaics has explored new possibilities for different smart applications with their advanced properties including flexibility, light-weight, and graded transparency. Low cost production and easy processing of organic solar cells comparing to conventional silicon-based solar cells make them interesting and worth employing for personal use and large scale applications . Today, the smart textiles as the part of technical textiles using smart materials including photoactive materials, conductive polymers, shape memory materials, etc. are developed to mimic the nature in order to form novel materials with a variety of functionalities. The solar cell-based textiles have found its application in various novel field and promising development obtaining new features. These photovoltaic textiles have found its application in military applications, where the soldiers need electricity for the portable devices in very remote areas. The photovoltaic textile materials can be used to manufacture power wearable, mobile and stationary electronic devices to communicate, lighten, cool and heat, etc. by converting sun light into electrical energy. The photovoltaic materials can be integrated onto the textile structures especially on clothes, however, the best promising results from an efficient photovoltaic fiber has to be come which can constitute a variety of smart textile structures and related products1.

Fossil fuels lead to the emission of CO2 and other pollutants and consequently human health is under pressure due to adverse environmental conditions. In consequence of that renewable energy options have been explored widely in last decades2-3.

Unprecedented characteristics of photovoltaic (PV) cells attract maximum attention in comparision of other renewable energy options which has been proved by remarkable growth in global photovoltaic market4.

Organic solar cells made of organic electronic materials based on liquid crystals, polymers, dyes, pigment etc. attracted maximum attention of scientific and industrial community due to low weight, graded transparency, low cost, low bending rigidity and environmental friendly processing potential5-6. Various photovoltaic materials and devices similar to solar

Flexible Photovoltaic Textiles for Smart Applications 45

Indium tin oxide (ITO) was used as a common transparent electrode in polymer-based solar cells due to its remarkable efficiency and ability of light transmission. However, it is quite expensive and generally too brittle to be used with flexible textile substrates. Therefore, highly conductive poly (3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) PEDOT:PSS, carbon nano-tube or metal layers are used to substitute ITO electrode. This can be a promising way to develop PV textiles for smart application due to its low cost and easy application features for future photovoltaic textile applications. A typical sequence of

**4. Manufacturing of organic photovoltaic cells** 

photovoltaic textiles manufacturing is exhibited in Fig. 2.

Fig. 2. A typical sequence of photovoltaic textiles manufacturing

large area organic thin layer photovoltaic cell device13.

two techniques:

**4.1 Roll-to-roll coating technique** 

A group of scientists has demonstrated the fabrication of an organic photovoltaic device with improved power conversion efficiency by reducing lateral contribution of series resistance between subcells through active area partitioning by introducing a patterned structure of insulating partitioning walls inside the device. Thus, the method of the present invention can be effectively used in the fabrication and development of a next-generation

The manufacturing of organic photovoltaic (PV) cells can be possible at reasonable cost by

A continuous roll-to-roll nanoimprint lithography (R2RNIL) technique can provide a solution for high-speed large-area nanoscale patterning with greatly improved throughput. In a typical

cells integrated with textile fabrics can harvest power by translating photon energy into electrical energy.
