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. This can be achieved either through the coupling of photovoltaic cells and electrolysis, or through direct sunlight conversion by photoelectrodes or photocatalysts, the latter being the focus of this talk. In solar conversion, there is often a critical kinetic mismatch between the lifetimes of initially generated photoexcited states and the timescales of charge extraction / catalysis. I will start my talk by introducing solar driven fuel synthesis, and the charge carrier lifetime challenge in photoelectrochemical and photocatalytic systems. I will contrast this with the smaller lifetime challenges in organic and perovskite solar cells. I will then go on to discuss some of our recent studies employing transient optical spectroscopies measuring charge carrier dynamics in photoelectrodes and photocatalysts and how these impact upon the efficiency of solar driven water splitting, covering a range of metal oxide and polymer materials. I will consider the importance of d-orbital occupancy in metal oxide photocatalysts in determining charge carrier lifetimes. I will then go on to discuss carbon nitride and organic polymer photocatalysts, and the impact of charge trapping and heterojunctions in extending the lifetime of charge carriers. I will conclude by contrast charge carrier dynamics on organic bulkheterojunction solar cells and photocatalysts nanoparticle suspensions, and in particular the ability of aqueous environments to supress charge carrier recombination.