Transition metal dichalcogenides (TMDCs), especially two-dimensional monolayers, exhibit strong excitonic binding energies (300 meV), large carrier mobilities (30 cm 2 /Vs) and high extinction coefficients (~3*10 6 cm -1 ). They are chemically versatile, compatible with silicon technology, relatively cheap, and can be used as monolayers, multilayers or combined with other 2D materials in heterostructures. These properties are ideal for their application in photodetectors with high speed and large detectivity at the same time. However, as detailed by Sorger et al. an independent optimization of speed and detectivity (or responsivity) is not possible, since the long carrier lifetimes needed for high responsivities are detrimental for the response time. Similarly, large mobilities are required for fast photodetection with sufficiently large band gaps to prevent high dark currents and, thus, low detectivities as e.g. in zero-gap graphene. Over the past ten years, most efforts have focused with impressive results on increasing the responsivity. In contrast, similar improvements of the response speed of TMDC photodetectors have been challenging, and in particular a GHz photoresponse has remained mostly elusive, despite an increasing demand for GHz-compatible photodetectors as components in optical data communication. In this account, we reflect on the lessons learnt from our own physical-chemical approaches toward ultrafast TMDCs photodetectors.