A facile and novel method has been developed to prepare ultrathin PbI₂ single crystals with good mechanical flexibility and bendability for high sensitivity photodetectors. The prototype lateral metal–semiconductor–metal photodetector based on the as-prepared crystal exhibits a responsivity of up to 11.3 A W⁻¹, a photogain of 31.84, and a high-speed photoresponse with a time constant of 354 μs.