Realizing terawatt-scale solar electricity: Nanotechnology-enabled physical mechanisms and material properties

Achieving a sustainable energy system is one of the defining challenges of the forthcoming decades. The importance and difficulty of developing an energy source that can replace the existing electrical infrastructure is often termed the terawatt (TW) challenge, which refers to the fact that to supply the energy demands of the globe, truly massive amounts of electricityTWsare needed [1], [2]. Since the term received broad public airing in 2005, addressing the TW challenge has been given additional impetus and become time critical due to the convergence of multiple issues including global warming; the scarcity, uneven geographical distribution, and cost of conventional resources, particularly oil; and other factors such as aging of existing infrastructure, the desirability of local electricity production, and the creation of jobs. At the same time that meeting the TW challenge has become more important, the continuing rapid expansion of renewable technologies has simultaneously offered a solution to the seemingly intractable problem. Seven years since the term was coined, the installed photovoltaic (PV) capacity has quadrupled, and the yearly PV installations in Germany, Spain, and Japan more than supplies the electricity due to growth in electricity demand. Yet even in these countries, the overall fraction of the electricity demand met by PV installations is only a few percent. For PV energy to make a larger contribution, both in the United States and worldwide, it must continue its rapid growth and expansion.