The Gratzel Cell: Where Next?

Twenty years after O'Regan and Gratzel's seminal Nature paper entitled "A Low-Cost, High-Efficiency Solar-Cell Based on Dye-Sensitized Colloidal TiO2 Films", dye-sensitized solar cells (DSCs) and analogous devices have become a major topic of research, with over 1000 papers published in 2010. Although much more is now known about the physical and chemical processes taking place during operation of the DSC, the exponential increase in research effort during this period has not been matched by large increases in efficiency. This raises questions regarding the nature of the barriers that are holding back progress and whether current research is adequately addressing the key issues that are currently limiting device performance. This Perspective attempts to identify some of the factors that determine DSC performance and, as part of a selective survey of recent research highlights, presents a personal view of new approaches and research strategies that could offer ways to overcome the current efficiency stalemate.