Bulk Heterojunctions in Photovoltaic Devices

Current solar cells, on the market today, have little room for improved efficiency or cost reduction. Part of this is due to the costly manufacture of high purity silicon and the current fabrication methods for solar cells. Solution processable solar cells would mark a great stride forward to cost reduction. If such cells can be demonstrated to be efficient enough and stable enough it would be a turning point in history. However, solution processable devices still need much work before they can compete in the market. This text addresses characterization problems in the TEM, covers a study dealing with optimization strategies for organic bulk heterojunction devices, and introduces a strikingly high efficiency perovskite device that has a bulk heterojunction like structure.

This text is arranged in four major portions; chapters 1 and 2, chapters 3 and 4, chapter 5, and chapter 6. The first two chapters give an introduction to some of the materials and microscopy techniques referred to throughout the text. Chapters 3 and 4 introduce a new sample thickness or density measurement technique (chapter 3), and illustrate how such a technique can be quite useful in studying organic photovoltaic materials by facilitating quantitative material fraction measurements (chapter 4). Next, chapter 5 details a study of organic photovoltaic systems highlighting optimization strategies. Specifically, chapter 5 describes the effect of various solvents and solvent annealing times on the P3HT/PCBM system. Finally, chapter 7 introduces a state-of-the-art, high efficiency perovskite device that exhibits large, single crystal domains as well as increased hole transport contact area through a bulk heterojunction like structure.