Lessons from transient spectroscopy on how charge dynamics in organic semiconductor nanoparticles determine photocatalytic function

There is increasing interest in harnessing sunlight to drive the synthesis of molecular fuels and chemicals, including in particular water photolysis to yield molecular oxygen and hydrogen. Whilst most research to date has focused on inorganic photoelectrodes and photocatalysts, there is now increasing interest in the use of organic semiconductors for sunlight to fuel applications. There has been substantial progress in recent years in the development of both photoelectrodes and photocatalysts based on organic semiconductors, motivated in particular by the energetic, spectral and morphological tunability of these materials. I will start my talk by introducing some of the recent progress in the use of organic semiconductors for solar to fuel applications. I will discuss the charge carrier lifetime challenge for solar to fuel applications, highlighting how this has parallels, but also differences, with organic solar cells and inorganic photocatalysts.   I will then go on to discuss some of our recent studies employing transient optical spectroscopies measuring charge carrier dynamics in organic photocatalysts and how these impact upon the efficiency of solar driven fuel synthesis, covering a range of organic polymer and small molecule materials for both water and carbon dioxide reduction.