The role of anode buffer layers in P3HT-PCBM based bulk heterojunction organic solar cells

Realizing cheap-end cost-effective electronics has been the principle motivation behind the research in organic photovoltaic (OPV) field. The promise of low cost relies on using semiconducting polymers which can be cheaply synthesized with electronic properties tailored according to need. These cheaper organic semiconductors can be wet-chemically processed at room temperature on flexible substrates. This entire process can be scaled up to large scale roll-to-roll process which opens the door to a new field of “plastic electronics”. OPV has been considered to be the next generation of photovoltaics. However, among other challenges, the understanding of efficient charge carrier extraction with the use of optimized buffer layer has been one of the major drawbacks in these OPV systems. In this PhD work, PEDOT:PSS has been used as a model anode buffer layer for a P3HT-PCBM based bulk heterojunction solar cells, used here as a standard organic solar cells. Although PEDOT:PSS is the most common buffer layer used in P3HT-PCBM based organic solar cells, it is not the most optimized anode buffer layer available. This thesis creates a path toward the understanding of buffer layers in organic solar cells based on P3HT-PCBM systems with a primary focus on the anode buffer layer. PEDOT:PSS has been used in the majority of this work as the standard buffer layer system for P3HT-PCBM active layer. It has been modified and treated with various additives and solvents in order to understand the mechanisms for device performance enhancement. A novel electropolymerization method for depositing the polythiophene anode buffer layer, namely the timedependent cyclic-potential-sweep method, was developed and successfully applied for enhanced performance of the organic solar cells. Similarly, the area dependence seen in OSCs while treating PEDOT:PSS with some additives and solvents has been systematically studied and explained with simple models.