Optical and Electrical Enhancement of Organic Solar Cells.

Abstract

Organic solar cells have the potential to offer low cost, mass produced, solar energy generation, but further research is required to increase efficiency, improve lifetime, and reduce production costs before the low cost goal can be achieved. Current research toward improving efficiency is focused on developing new materials with better absorption and charge transport properties, and on improving morphology. There are other pursuits that could also significantly improve efficiency yet are relatively neglected by researchers. Two of these are optical light trapping to increase absorption and control of interfaces to reduce energy loss. This thesis makes contributions to both of these goals in three ways. First, some surprising results from the optical modeling of organic solar cells at non-normal incidence are described. Second, a general method for assessing the potential of a promising light trapping geometry is introduced, and discrepancies between modeling and experiment of that structure are explained. Finally, the effect of air exposure on single material and bulk heterojunction solar cells with InGa cathode is investigated. Air exposure is found to increase open circuit voltage, and using this method the open circuit voltage of a common organic solar cell system is increased by 15%. This work exposes the current lack of knowledge of many aspects of band structure in organic solar cells which suggests the need for more research in this area.