Lateral size dependence of photoconductivity in TMD networks

Photoconductivity is an important feature of semiconductors that finds major attention in the fields of solar cells, hydrogen and oxygen evolution reactions, and photodetectors. This feature involves a change of density of charge carriers induced by light, which is dependent on the generation of light-induced carriers and the recombination of excitons. This phenomenon has been observed in transition metal dichalcogenides (TMDs) since 2010; however, when printing such materials on flexible substrates, they form networks that would exhibit distinct transport characteristics compared to isolated TMDs crystals. In this work, TMD nanosheets are printed by vacuum filtering and their photoconductivity was measured by using a xenon lamp inside an obscure chamber. Molybdenum disulfide-based devices show higher responsivity as compared with tungsten disulfide devices, which is attributed to an increased light absorption and hydroxyl groups attached to the surface of the MoS₂networks that enhance the photoconductivity by increasing the carrier lifetimes. Furthermore, the responsivity of the devices behaves similarly to the conductivity, which is modeled as networks of pairs of nanosheets and junctions through percolative paths. Finally, this is the first report that shows that the response time of the devices increases with lateral size.