There are multiple ways to improve photovoltaic performance by means of nanostructures in solar cells: (1) employing new physical approaches in order to reach thermodynamic limits; (2) allowing solar cells to more closely approximate their material-dependent thermodynamic limits; and (3) providing new routes for low-cost fabrication by self-assembly or design of new materials. We focus primarily on the first two avenues, both of which have the goal of increasing efficiency.
Several different approaches will be described that circumvent long-held physical assumptions and lead beyond first- and second-generation solar cell technologies. Special emphasis will be on a novel nanostructure-based devices based on advanced concepts such as hot carrier cells, intermediate band and multi-exciton generation, which offer the theoretical basis to realize high-efficiency energy conversion. In particular, we focus on the role of ultrafast carrier dynamics in nanostructures in terms of the competition between carrier extraction processes and energy relaxation processes that convert electron kinetic energy into heat. We also focus on the effects that surfaces and interfaces play in nanostructured solar cells, and on how to reduce parasitic carrier recombination effects through passivation.