To reach its full potential, photovoltaics has to evolve to a thin film implementation with energy conversion efficiency higher than that offered by the standard photovoltaic conversion process. Tandem or stacked cells offer the most widely demonstrated approach for such efficiency improvement but are usually associated with high costs.
A potentially lower cost option, based on silicon quantum dots embedded in a dielectric matrix, is being explored by the author's group. The nanostructure material's band gap is controlled by varying the diameter of the quantum dots. The same technology is also being investigated as a vehicle for implementing "hot carrier" cells that have the same limiting efficiency as a large stack of cells but would be capable of being implemented in a simpler 2-terminal device. However, at present, the structure poses even more daunting physical challenges. Recent theoretical and experimental progress with both concepts will be described.