Solution-Processed 2D PbS Nanoplates with Residual Cu2S Exhibiting Low Resistivity and High Infrared Responsivity

We report the synthesis of colloidal 2D PbS nanoplates with residual Cu2S domains via a partial cation-exchange process involving Pb2+ and presynthesized hexagonal Cu2S nanoplates with an average thickness of similar to 3 nm and edge lengths of similar to 150 nm. Different from previously reported PbS nanosheets whose basal planes are +/-{100}(PbS), our approach yields nanoplates whose basal planes are +/-{111}(PbS), which was previously theoretically predicted to have better surface ligand passivation. Subsequently, we found that the PbS nanoplates showed improved colloidal stability and did not suffer from severe aggregation despite numerous solvent wash steps. We further incorporated a film of nanoplates into a planar photodetector device with lateral Au electrodes. The amount of residual Cu2S in the PbS nanoplates, which can be tuned by adjusting the reaction time of the cation-exchange process, was found to play a crucial role in determining the in-plane conductivity of the film and therefore its photodetection efficiency. For PbS nanoplates with 7.8% residual Cu+, the responsivity and specific detectivity at 808 nm was similar to 1739 A/W and similar to 1.55 x 10(11) Jones, respectively. The high responsivity was attributed to the very low PbS nanoplate film resistivity of 8.04 ohm-cm, which is comparable to commercial doped semiconductors.