ABSTRACT
Dye-sensitized solar cells [1-4] are the most promising alternative to conventional solar cells conceived in recent years. They convert light to electricity by a mechanism that is different from conventional cells. These differences provide an opportunity to further our understanding of the essential requirements for all solar cells and for this reason, among many others, the study of dye-sensitized solar cells (DSSCs or dye cells) is a fruitful area of research. It also brings us closer to the ultimate goal of designing and producing highly efficient, inexpensive solar cells. A key difference between dye cells and conventional solar cells, epitomized by silicon p-n junction cells, is the relative importance of interfacial processes. Conventional solar cells are minority carrier devices: Their efficiency is determined by the ability of photogenerated minority carriers (say, electrons in a p-type material) to escape from that side of the device before recombining with the majority carriers. Thus, properties such as the minority carrier lifetime and diffusion length are essential to device function. Although interfaces are also important in these devices, the crucial charge-carrier processes of photogeneration, separation, and recombination, all occur primarily in the bulk material. Therefore, bulk semiconductor properties such as crystallinity and chemical purity often control the efficiency of conventional solar cells, and optimizing these properties can be expensive.
