Organic and Hybrid Photovoltaics- Approaches to improve the performances

Abstract : Organic materials, small molecules and polymers, are generally considered as insulators till the discovery of conducting polymers in 1977 by Prof A J Heeger, Prof Shirakawa and Prof A G McDiramid. Henceforth a lot of work had been done to understand the conducting properties of such materials. In 1990, Cavendish group demonstrated electroluminescent devices using such materials, which opened an area of organic semiconductors and its applications in optoelectronic devices. Even though there are debates about the origin of band gaps in terms of a band picture and a molecular picture, experimental evidence favors a molecular approach for exploring the semiconducting properties of organic semiconductors. Here we will be discussing the application of organic semiconductors for photovoltaic applications. The solution process ability, tuning of the band gap and flexibility are some of the attracting features other than economic advantages, over silicone, which has propelled active research in this area. In this presentation, we will be discussing some of the approaches; we have taken to address improvement in the performance of such devices. Some of the factors affecting the performance of organic photovoltaic are absorption, exciton diffusion, exciton dissociation, charge carrier generation and charge transfer. We have used approaches such as, bulk hetero-junction device structure, incorporation of plasmonic structure in different layers of the photovoltaic devices. modifying inter facial layers and inverted solar cell structure to improve the performances of the photovoltaic devices. Small molecules such as squaraine, which is mono-dispersive with an absorption extending to near infra red region is used to address the polydispersivity, purity issues and high band gap nature of polymers. Organic inorganic hybrid materials, such as perovskites are used to make photovoltaic devices, where the free carriers have a longer diffusion length compared to that of organic materials.In our presentation we will discuss these approaches in detail.