Review on recent advances in polythiophene based photovoltaic devices

Discovery of conducting polymer introduced us to the total polymeric solar cells (PSC). During the last decade, power conversion efficiency (PCE) of these solar cells has increased from 1% to 11.5% (with the bulk heterojunction concept). Though they are still behind their inorganic counterparts in terms of efficiency, these solar cells have several advantages, such as scalability, it is printable, we can get flexible solar panels and low cost, etc. This comparatively lower efficiency is the key driving force behind the ongoing research and development on organic photovoltaics. Functionalized polythiophenes are the most studied donors and hole transporting materials in this technology (total polymer and polymer based hybrid solar cells). Like all other conducting polymers, pure polythiophene (un-substituted) is difficult to process, but its processability can be improved through the addition of functional moieties, mostly alkyl side chains. These modified polyalkylthiophenes are relatively stable, processable and have excellent optical and electrical properties. For examples, poly (3,4-ethylenedioxythiophene) doped with poly (styrenesulfonate) (PEDOT:PSS) and poly (3-hexylthiophene) (P3HT) are the most investigated materials. Here, in this review article, we have summarized some of the important modification techniques of thiophene monomer to get the desired polymers, its features and recent uses in the polymer based solar cells.