The physics and optimization of organic thin film photovoltaic cells.

摘要

Organic materials have the potential to provide low-cost photovoltaic devices for solar energy conversion. In this thesis, we focus on understanding the physics of organic photovoltaic cells based on small molecular weight materials, and how best to exploit that understanding to optimize device performance.; First, we explain the various processes that lead to photodetection in organic materials, and the limiting factors that contribute to the various efficiencies at each step. Then, the basic architectures for photovoltaic devices are described. These include the donor-acceptor heterojunction for efficient exciton dissociation, the exciton blocking layer, and the stacked cell. We show how the choice of materials with known energy levels affects device performance, particularly the open-circuit voltage and the short-circuit and dark current densities. The roles of each of these factors is approached from a fundamental standpoint, describing, for example, how the exciton blocking layer functions, and how surface plasmon resonances in silver clusters can enhance absorption and, therefore, device efficiency in stacked cells.; We also discuss the properties and use of both mixed donor-acceptor thin films and homogeneous layers in devices. By investigating, in detail, the material and device properties of the mixed films, we show that a tradeoff exists between reduced charge transport in the mixture and increased exciton dissociation and charge generation. Through the use of new materials, we demonstrate the ability for organic materials to harvest infrared radiation, an important step in increasing the absorption spectrum of a stacked cell. Using all of these various techniques, it is shown how record efficiencies have been achieved.