The cost of the present generation of inorganic silicon solar cells is very high and further breakthroughs in cost and efficiency using traditional materials are becoming less and less likely after over 50 years of development. Next generation organic solar cells offer a solution to the limitations of silicon through the vision of low-cost, liquid-based, large area fabrication technology based on polymer and nanomaterials at room temperature. However, most polymers used in solar cells are dissolved in organic solvents such as xylene, toluene, chloroform, and chlorobenzene. Such solvents are harmful to people and environments, leading to higher costs due to complicated waste disposal processing. This is in conflict with the low cost, green, and renewable energy for which we are aiming. To realize a green organic solar cell, a novel solar cell has been created using an environmentally friendly water-soluble thiophene polymer [(Sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate])] (PTEBS) and nanocrystalline TiO2. This novel system has shown great potential in photovoltaics the work has garnered the attention of the international community.In our innovative solar cells, the water-soluble polythiophene (PTEBS) is used as electron donor. Nanoparticle TiO2 acts as electron acceptor. PTEBS/TiO2 solar cells with various structures including bilayer heterojunctions, bulk heterojunctions and a hybrid of bilayer and bulk heterojunctions have been developed and explored. These results are comparable to the best polymer/metal-oxide solar cells reported by other groups using organic solvents.In summary, this is the first time that green solar cells have been fabricated from environmentally friendly water-soluble polymers. By using water as the solvent and utilizing liquid-based processing, the cost of the energy generated by this type of solar cell will be further lowered. In addition, the flexible polymer offers the ease of fabrication and integration into different devices
