Intermediate band solar cells: Present and future

Abstract In the quest for high‐efficiency photovoltaics (PV), the intermediate band solar cell (IBSC) was proposed in 1997 as an alternative to tandem solar cells. The IBSC offers 63% efficiency under maximum solar concentration using a single semiconductor material. This high‐efficiency limit attracted the attention of the PV community, yielding to numerous intermediate band (IB) studies and IBSC prototypes employing a plethora of candidate IB materials. As a consequence, the principles of operation of the IBSC have been demonstrated, and the particularities and difficulties inherent to each different technological implementation of the IBSC have been reasonably identified and understood. From a theoretical and experimental point of view, the IBSC research has reached a mature stage. Yet we feel that, driven by the large number of explored materials and technologies so far, there is some confusion about what route the IBSC research should take to transition from the proof of concept to high efficiency. In this work, we give our view on which the next steps should be. For this, first, we briefly review the theoretical framework of the IBSC, the achieved experimental milestones, and the different technological approaches used, with special emphasis on those recently proposed.