Understanding the physics of Carrier-Multiplication and intermediate-band solar cells based on nanostructures - What is going on?

The concepts of (1) Carrier-Multiplication (CM - ¿two electron-hole pairs from one photon¿) and (2) Intermediate Band Solar Cell (IBSC) based on nanostructures, have created significant interest and excitement, but, at the same time, raised questions pertaining to the approaches used to argue their validity. In part, confusion arose because the initial arguments made were based on rather qualitative, if not nai¿ve, physical models. Here we propose to use the tools of modern theory of nanostructures for examining these concepts. Simple but surprising physical pictures emerge from such complex atomistic calculations. We will review and discuss the underlying concepts and experiments surrounding CM and quantum dot-based IBSC, delineating fact from fiction, and pointing to some new, important unanswered questions.