Solar Cells

In this review chapter, we present the current state of the art of photovoltaic device technology. We begin with an overview of the fundamentals of solar cell device operation, and the nature of the solar energy spectrum and light absorption in devices. We then go into detail of the basics of solar cell operation, and the effects of various factors on the primary figures of merit, the open circuit voltage, short circuit current, and fill factor. In particular we focus on recombination, both in terms of the photocurrent and the dark current affecting the cell voltage. We then discuss heterojunction solar cells, and the general concept of carrier selective structures, which improve solar cell performance. We summarize the main single junction technologies and their efficiencies historically, starting with Si wafer-based technology and GaAs, then thin film technology, and organic solar cells, ending with recent developments of hybrid perovskite-based solar cells. The limits of solar cell performance in terms of energy conversion efficiency are discussed, where we introduce the concept of detailed balance to derive the Shockley-Queisser limit for single junction cells. Methods of circumventing this single gap limit are discussed, which set the stage for discussing multijunction or tandem solar cells which currently hold the record for highest conversion efficiency in any solar technology. We then discuss nanotechnology in general, and how it is increasingly incorporated in modern solar cells. In this context, we discuss the use of nanostructures in improving light management in solar cells by enhancing light trapping beyond the classical limit. We discuss quantum dot/nanoparticle-based cells such as dye-sensitized solar cells and nanowire solar cells. Finally, we conclude by discussing advanced concept solar cell structures such as intermediate band, multiexciton generation, and hot carrier solar cells, and their theoretical capability of greatly exceeding the Shockley-Queisser limit.