The advent of tin diselenide (SnSe 2) enables novel pathways for optoelectronics, due to its reduced cost, ultralow thermal conductivity and high potential for thermoelectricity. To date, SnSe 2-based optoelectronic devices have been focused on the visible and infrared range of the electromagnetic spectrum, with efficiency sharply decreasing at longer wavelength. Here, we present SnSe 2 photodetectors with exfoliated SnSe 2 nanosheets extended in the range of terahertz frequency exhibiting high responsivity (170 VW-1), fast speed (2.2 μs), as well as room-temperature operation, based on efficient production of hotelectrons under deep-subwavelength electromagnetic focus, which outperform thermal-based photodetectors. Our SnSe 2-based detectors show high-contrast imaging from terahertz up to visible. The outstanding ambient stability of our broadband photodetectors in a timescale of months is due to the …