Given their established robustness and favorable optoelectronic properties, the semiconducting transition metal dichalcogenides (TMDs, e.g. MoS2 and WSe2) are attractive for solar energy application. Recent advances in the solvent-assisted exfoliated of TMDs into 2D nanoflakes suggests that inexpensive roll-to-roll processing can be used to prepare TMD devices inexpensively over large area. However, the high concentration of edge defects in these materials act as recombination sites for photogenerated carriers. In this presentation the challenges with charge transport, separation, recombination and interfacial transfer in these systems will be discussed with respect to the 2D flake size and defect passivation/charge extraction treatments. Our results give insight into the roles of edge and bulk defects and suggest routes for improvement. Overall it is shown that TMDs can achieve internal quantum efficiency for photon harvesting similar to bulk single crystal samples. Moreover, promising performance is demonstrated for the direct solar to fuel coversion using WSe2 as a photocathode for water reduction.
 X. Yu, K. Sivula, ACS Energy Letters 2016, 1, 315.
 X. Yu, M. S. Prevot, N. Guijarro, K. Sivula, Nat Commun 2015, 6, 7596.
 X. Yu, A. Rahmanudin, X. A. Jeanbourquin, D. Tsokkou, N. Guijarro, N. Banerji, K. Sivula, ACS Energy Letters 2017, 2, 524.