Redox electrolytes have proven to be extremely important in determining the performance of dye-sensitized solar cells (DSCs). The design and understanding of the redox couple, especially iodide free systems, has become a recent focus of DSC electrolyte research. In this perspective article, advances in the conception and performance of various redox shuttles including molecular hole transport materials are reviewed with respect to their structure and the charge transfer dynamics at the counter electrode. In particular the discussion will focus on the trends that enable iodide-free redox couples to be the most effective and their feasibility to be used in DSCs in combination with new and innovative sensitizers and counter electrode materials.
