In search of a true hot carrier solar cell

Several decades ago, it was proposed that one could improve the single junction solar cell by the concentration of effort onto the hot carriers. In the intervening years, no significant progress has been made in this direction, although the effort continues to involve a large body of workers. While this community is focused on the role of phonons and selectively measuring only a fraction of the energy spectrum, it has not generally addressed the true usage of the hot carriers that can be supported in the system. Here, we discuss a different approach relying upon the use of 'metastable' levels provided by the satellite valleys of the conduction band. Such usage retains the hot carriers at higher energy levels than normal, and promises to provide the long-sought improvement with hot carrier solar cells.